Android example source code file (HorizontalScrollView.java)

This example Android source code file (HorizontalScrollView.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

android, animated_scroll_gap, attributeset, content, drawing, horizontalscrollview, illegalstateexception, invalid_pointer, list, marginlayoutparams, max_scroll_factor, override, paint, rect, scroller, ui, util, velocitytracker, view, viewparent

The HorizontalScrollView.java Android example source code

/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.widget;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.FocusFinder;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.view.animation.AnimationUtils;

import java.util.List;

/**
 * Layout container for a view hierarchy that can be scrolled by the user,
 * allowing it to be larger than the physical display.  A HorizontalScrollView
 * is a {@link FrameLayout}, meaning you should place one child in it
 * containing the entire contents to scroll; this child may itself be a layout
 * manager with a complex hierarchy of objects.  A child that is often used
 * is a {@link LinearLayout} in a horizontal orientation, presenting a horizontal
 * array of top-level items that the user can scroll through.
 *
 * <p>You should never use a HorizontalScrollView with a {@link ListView}, since
 * ListView takes care of its own scrolling.  Most importantly, doing this
 * defeats all of the important optimizations in ListView for dealing with
 * large lists, since it effectively forces the ListView to display its entire
 * list of items to fill up the infinite container supplied by HorizontalScrollView.
 *
 * <p>The {@link TextView} class also
 * takes care of its own scrolling, so does not require a ScrollView, but
 * using the two together is possible to achieve the effect of a text view
 * within a larger container.
 *
 * <p>HorizontalScrollView only supports horizontal scrolling.
 */
public class HorizontalScrollView extends FrameLayout {
    private static final int ANIMATED_SCROLL_GAP = ScrollView.ANIMATED_SCROLL_GAP;

    private static final float MAX_SCROLL_FACTOR = ScrollView.MAX_SCROLL_FACTOR;


    private long mLastScroll;

    private final Rect mTempRect = new Rect();
    private Scroller mScroller;

    /**
     * Flag to indicate that we are moving focus ourselves. This is so the
     * code that watches for focus changes initiated outside this ScrollView
     * knows that it does not have to do anything.
     */
    private boolean mScrollViewMovedFocus;

    /**
     * Position of the last motion event.
     */
    private float mLastMotionX;

    /**
     * True when the layout has changed but the traversal has not come through yet.
     * Ideally the view hierarchy would keep track of this for us.
     */
    private boolean mIsLayoutDirty = true;

    /**
     * The child to give focus to in the event that a child has requested focus while the
     * layout is dirty. This prevents the scroll from being wrong if the child has not been
     * laid out before requesting focus.
     */
    private View mChildToScrollTo = null;

    /**
     * True if the user is currently dragging this ScrollView around. This is
     * not the same as 'is being flinged', which can be checked by
     * mScroller.isFinished() (flinging begins when the user lifts his finger).
     */
    private boolean mIsBeingDragged = false;

    /**
     * Determines speed during touch scrolling
     */
    private VelocityTracker mVelocityTracker;

    /**
     * When set to true, the scroll view measure its child to make it fill the currently
     * visible area.
     */
    private boolean mFillViewport;

    /**
     * Whether arrow scrolling is animated.
     */
    private boolean mSmoothScrollingEnabled = true;

    private int mTouchSlop;
    private int mMinimumVelocity;
    private int mMaximumVelocity;
    
    /**
     * ID of the active pointer. This is used to retain consistency during
     * drags/flings if multiple pointers are used.
     */
    private int mActivePointerId = INVALID_POINTER;
    
    /**
     * Sentinel value for no current active pointer.
     * Used by {@link #mActivePointerId}.
     */
    private static final int INVALID_POINTER = -1;
    
    public HorizontalScrollView(Context context) {
        this(context, null);
    }

    public HorizontalScrollView(Context context, AttributeSet attrs) {
        this(context, attrs, com.android.internal.R.attr.horizontalScrollViewStyle);
    }

    public HorizontalScrollView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        initScrollView();

        TypedArray a = context.obtainStyledAttributes(attrs,
                android.R.styleable.HorizontalScrollView, defStyle, 0);

        setFillViewport(a.getBoolean(android.R.styleable.HorizontalScrollView_fillViewport, false));

        a.recycle();
    }

    @Override
    protected float getLeftFadingEdgeStrength() {
        if (getChildCount() == 0) {
            return 0.0f;
        }

        final int length = getHorizontalFadingEdgeLength();
        if (mScrollX < length) {
            return mScrollX / (float) length;
        }

        return 1.0f;
    }

    @Override
    protected float getRightFadingEdgeStrength() {
        if (getChildCount() == 0) {
            return 0.0f;
        }

        final int length = getHorizontalFadingEdgeLength();
        final int rightEdge = getWidth() - mPaddingRight;
        final int span = getChildAt(0).getRight() - mScrollX - rightEdge;
        if (span < length) {
            return span / (float) length;
        }

        return 1.0f;
    }

    /**
     * @return The maximum amount this scroll view will scroll in response to
     *   an arrow event.
     */
    public int getMaxScrollAmount() {
        return (int) (MAX_SCROLL_FACTOR * (mRight - mLeft));
    }


    private void initScrollView() {
        mScroller = new Scroller(getContext());
        setFocusable(true);
        setDescendantFocusability(FOCUS_AFTER_DESCENDANTS);
        setWillNotDraw(false);
        final ViewConfiguration configuration = ViewConfiguration.get(mContext);
        mTouchSlop = configuration.getScaledTouchSlop();
        mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();
        mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
    }

    @Override
    public void addView(View child) {
        if (getChildCount() > 0) {
            throw new IllegalStateException("HorizontalScrollView can host only one direct child");
        }

        super.addView(child);
    }

    @Override
    public void addView(View child, int index) {
        if (getChildCount() > 0) {
            throw new IllegalStateException("HorizontalScrollView can host only one direct child");
        }

        super.addView(child, index);
    }

    @Override
    public void addView(View child, ViewGroup.LayoutParams params) {
        if (getChildCount() > 0) {
            throw new IllegalStateException("HorizontalScrollView can host only one direct child");
        }

        super.addView(child, params);
    }

    @Override
    public void addView(View child, int index, ViewGroup.LayoutParams params) {
        if (getChildCount() > 0) {
            throw new IllegalStateException("HorizontalScrollView can host only one direct child");
        }

        super.addView(child, index, params);
    }

    /**
     * @return Returns true this HorizontalScrollView can be scrolled
     */
    private boolean canScroll() {
        View child = getChildAt(0);
        if (child != null) {
            int childWidth = child.getWidth();
            return getWidth() < childWidth + mPaddingLeft + mPaddingRight ;
        }
        return false;
    }

    /**
     * Indicates whether this ScrollView's content is stretched to fill the viewport.
     *
     * @return True if the content fills the viewport, false otherwise.
     */
    public boolean isFillViewport() {
        return mFillViewport;
    }

    /**
     * Indicates this ScrollView whether it should stretch its content width to fill
     * the viewport or not.
     *
     * @param fillViewport True to stretch the content's width to the viewport's
     *        boundaries, false otherwise.
     */
    public void setFillViewport(boolean fillViewport) {
        if (fillViewport != mFillViewport) {
            mFillViewport = fillViewport;
            requestLayout();
        }
    }

    /**
     * @return Whether arrow scrolling will animate its transition.
     */
    public boolean isSmoothScrollingEnabled() {
        return mSmoothScrollingEnabled;
    }

    /**
     * Set whether arrow scrolling will animate its transition.
     * @param smoothScrollingEnabled whether arrow scrolling will animate its transition
     */
    public void setSmoothScrollingEnabled(boolean smoothScrollingEnabled) {
        mSmoothScrollingEnabled = smoothScrollingEnabled;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        if (!mFillViewport) {
            return;
        }

        final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        if (widthMode == MeasureSpec.UNSPECIFIED) {
            return;
        }

        if (getChildCount() > 0) {
            final View child = getChildAt(0);
            int width = getMeasuredWidth();
            if (child.getMeasuredWidth() < width) {
                final FrameLayout.LayoutParams lp = (LayoutParams) child.getLayoutParams();
    
                int childHeightMeasureSpec = getChildMeasureSpec(heightMeasureSpec, mPaddingTop
                        + mPaddingBottom, lp.height);
                width -= mPaddingLeft;
                width -= mPaddingRight;
                int childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(width, MeasureSpec.EXACTLY);
    
                child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
            }
        }
    }

    @Override
    public boolean dispatchKeyEvent(KeyEvent event) {
        // Let the focused view and/or our descendants get the key first
        return super.dispatchKeyEvent(event) || executeKeyEvent(event);
    }

    /**
     * You can call this function yourself to have the scroll view perform
     * scrolling from a key event, just as if the event had been dispatched to
     * it by the view hierarchy.
     *
     * @param event The key event to execute.
     * @return Return true if the event was handled, else false.
     */
    public boolean executeKeyEvent(KeyEvent event) {
        mTempRect.setEmpty();

        if (!canScroll()) {
            if (isFocused()) {
                View currentFocused = findFocus();
                if (currentFocused == this) currentFocused = null;
                View nextFocused = FocusFinder.getInstance().findNextFocus(this,
                        currentFocused, View.FOCUS_RIGHT);
                return nextFocused != null && nextFocused != this &&
                        nextFocused.requestFocus(View.FOCUS_RIGHT);
            }
            return false;
        }

        boolean handled = false;
        if (event.getAction() == KeyEvent.ACTION_DOWN) {
            switch (event.getKeyCode()) {
                case KeyEvent.KEYCODE_DPAD_LEFT:
                    if (!event.isAltPressed()) {
                        handled = arrowScroll(View.FOCUS_LEFT);
                    } else {
                        handled = fullScroll(View.FOCUS_LEFT);
                    }
                    break;
                case KeyEvent.KEYCODE_DPAD_RIGHT:
                    if (!event.isAltPressed()) {
                        handled = arrowScroll(View.FOCUS_RIGHT);
                    } else {
                        handled = fullScroll(View.FOCUS_RIGHT);
                    }
                    break;
                case KeyEvent.KEYCODE_SPACE:
                    pageScroll(event.isShiftPressed() ? View.FOCUS_LEFT : View.FOCUS_RIGHT);
                    break;
            }
        }

        return handled;
    }

    private boolean inChild(int x, int y) {
        if (getChildCount() > 0) {
            final int scrollX = mScrollX;
            final View child = getChildAt(0);
            return !(y < child.getTop()
                    || y >= child.getBottom()
                    || x < child.getLeft() - scrollX
                    || x >= child.getRight() - scrollX);
        }
        return false;
    }
    
    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        /*
         * This method JUST determines whether we want to intercept the motion.
         * If we return true, onMotionEvent will be called and we do the actual
         * scrolling there.
         */

        /*
        * Shortcut the most recurring case: the user is in the dragging
        * state and he is moving his finger.  We want to intercept this
        * motion.
        */
        final int action = ev.getAction();
        if ((action == MotionEvent.ACTION_MOVE) && (mIsBeingDragged)) {
            return true;
        }

        switch (action & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_MOVE: {
                /*
                 * mIsBeingDragged == false, otherwise the shortcut would have caught it. Check
                 * whether the user has moved far enough from his original down touch.
                 */

                /*
                * Locally do absolute value. mLastMotionX is set to the x value
                * of the down event.
                */
                final int activePointerId = mActivePointerId;
                if (activePointerId == INVALID_POINTER) {
                    // If we don't have a valid id, the touch down wasn't on content.
                    break;
                }

                final int pointerIndex = ev.findPointerIndex(activePointerId);
                final float x = ev.getX(pointerIndex);
                final int xDiff = (int) Math.abs(x - mLastMotionX);
                if (xDiff > mTouchSlop) {
                    mIsBeingDragged = true;
                    mLastMotionX = x;
                    if (mParent != null) mParent.requestDisallowInterceptTouchEvent(true);
                }
                break;
            }

            case MotionEvent.ACTION_DOWN: {
                final float x = ev.getX();
                if (!inChild((int) x, (int) ev.getY())) {
                    mIsBeingDragged = false;
                    break;
                }
                
                /*
                 * Remember location of down touch.
                 * ACTION_DOWN always refers to pointer index 0.
                 */
                mLastMotionX = x;
                mActivePointerId = ev.getPointerId(0);

                /*
                * If being flinged and user touches the screen, initiate drag;
                * otherwise don't.  mScroller.isFinished should be false when
                * being flinged.
                */
                mIsBeingDragged = !mScroller.isFinished();
                break;
            }

            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP:
                /* Release the drag */
                mIsBeingDragged = false;
                mActivePointerId = INVALID_POINTER;
                break;
            case MotionEvent.ACTION_POINTER_UP:
                onSecondaryPointerUp(ev);
                break;
        }

        /*
        * The only time we want to intercept motion events is if we are in the
        * drag mode.
        */
        return mIsBeingDragged;
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {

        if (ev.getAction() == MotionEvent.ACTION_DOWN && ev.getEdgeFlags() != 0) {
            // Don't handle edge touches immediately -- they may actually belong to one of our
            // descendants.
            return false;
        }

        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain();
        }
        mVelocityTracker.addMovement(ev);

        final int action = ev.getAction();

        switch (action & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN: {
                final float x = ev.getX();
                if (!(mIsBeingDragged = inChild((int) x, (int) ev.getY()))) {
                    return false;
                }

                /*
                 * If being flinged and user touches, stop the fling. isFinished
                 * will be false if being flinged.
                 */
                if (!mScroller.isFinished()) {
                    mScroller.abortAnimation();
                }

                // Remember where the motion event started
                mLastMotionX = x;
                mActivePointerId = ev.getPointerId(0);
                break;
            }
            case MotionEvent.ACTION_MOVE:
                if (mIsBeingDragged) {
                    // Scroll to follow the motion event
                    final int activePointerIndex = ev.findPointerIndex(mActivePointerId);
                    final float x = ev.getX(activePointerIndex);
                    final int deltaX = (int) (mLastMotionX - x);
                    mLastMotionX = x;

                    scrollBy(deltaX, 0);
                }
                break;
            case MotionEvent.ACTION_UP:
                if (mIsBeingDragged) {
                    final VelocityTracker velocityTracker = mVelocityTracker;
                    velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
                    int initialVelocity = (int) velocityTracker.getXVelocity(mActivePointerId);

                    if (getChildCount() > 0 && Math.abs(initialVelocity) > mMinimumVelocity) {
                        fling(-initialVelocity);
                    }
                    
                    mActivePointerId = INVALID_POINTER;
                    mIsBeingDragged = false;

                    if (mVelocityTracker != null) {
                        mVelocityTracker.recycle();
                        mVelocityTracker = null;
                    }
                }
                break;
            case MotionEvent.ACTION_CANCEL:
                if (mIsBeingDragged && getChildCount() > 0) {
                    mActivePointerId = INVALID_POINTER;
                    mIsBeingDragged = false;
                    if (mVelocityTracker != null) {
                        mVelocityTracker.recycle();
                        mVelocityTracker = null;
                    }
                }
                break;
            case MotionEvent.ACTION_POINTER_UP:
                onSecondaryPointerUp(ev);
                break;
        }
        return true;
    }
    
    private void onSecondaryPointerUp(MotionEvent ev) {
        final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >>
                MotionEvent.ACTION_POINTER_INDEX_SHIFT;
        final int pointerId = ev.getPointerId(pointerIndex);
        if (pointerId == mActivePointerId) {
            // This was our active pointer going up. Choose a new
            // active pointer and adjust accordingly.
            // TODO: Make this decision more intelligent.
            final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
            mLastMotionX = ev.getX(newPointerIndex);
            mActivePointerId = ev.getPointerId(newPointerIndex);
            if (mVelocityTracker != null) {
                mVelocityTracker.clear();
            }
        }
    }
    
    private int getScrollRange() {
        int scrollRange = 0;
        if (getChildCount() > 0) {
            View child = getChildAt(0);
            scrollRange = Math.max(0,
                    child.getWidth() - getWidth() - mPaddingLeft - mPaddingRight);
        }
        return scrollRange;
    }

    /**
     * <p>
     * Finds the next focusable component that fits in this View's bounds
     * (excluding fading edges) pretending that this View's left is located at
     * the parameter left.
     * </p>
     *
     * @param leftFocus          look for a candidate is the one at the left of the bounds
     *                           if leftFocus is true, or at the right of the bounds if leftFocus
     *                           is false
     * @param left               the left offset of the bounds in which a focusable must be
     *                           found (the fading edge is assumed to start at this position)
     * @param preferredFocusable the View that has highest priority and will be
     *                           returned if it is within my bounds (null is valid)
     * @return the next focusable component in the bounds or null if none can be found
     */
    private View findFocusableViewInMyBounds(final boolean leftFocus,
            final int left, View preferredFocusable) {
        /*
         * The fading edge's transparent side should be considered for focus
         * since it's mostly visible, so we divide the actual fading edge length
         * by 2.
         */
        final int fadingEdgeLength = getHorizontalFadingEdgeLength() / 2;
        final int leftWithoutFadingEdge = left + fadingEdgeLength;
        final int rightWithoutFadingEdge = left + getWidth() - fadingEdgeLength;

        if ((preferredFocusable != null)
                && (preferredFocusable.getLeft() < rightWithoutFadingEdge)
                && (preferredFocusable.getRight() > leftWithoutFadingEdge)) {
            return preferredFocusable;
        }

        return findFocusableViewInBounds(leftFocus, leftWithoutFadingEdge,
                rightWithoutFadingEdge);
    }

    /**
     * <p>
     * Finds the next focusable component that fits in the specified bounds.
     * </p>
     *
     * @param leftFocus look for a candidate is the one at the left of the bounds
     *                  if leftFocus is true, or at the right of the bounds if
     *                  leftFocus is false
     * @param left      the left offset of the bounds in which a focusable must be
     *                  found
     * @param right     the right offset of the bounds in which a focusable must
     *                  be found
     * @return the next focusable component in the bounds or null if none can
     *         be found
     */
    private View findFocusableViewInBounds(boolean leftFocus, int left, int right) {

        List<View> focusables = getFocusables(View.FOCUS_FORWARD);
        View focusCandidate = null;

        /*
         * A fully contained focusable is one where its left is below the bound's
         * left, and its right is above the bound's right. A partially
         * contained focusable is one where some part of it is within the
         * bounds, but it also has some part that is not within bounds.  A fully contained
         * focusable is preferred to a partially contained focusable.
         */
        boolean foundFullyContainedFocusable = false;

        int count = focusables.size();
        for (int i = 0; i < count; i++) {
            View view = focusables.get(i);
            int viewLeft = view.getLeft();
            int viewRight = view.getRight();

            if (left < viewRight && viewLeft < right) {
                /*
                 * the focusable is in the target area, it is a candidate for
                 * focusing
                 */

                final boolean viewIsFullyContained = (left < viewLeft) &&
                        (viewRight < right);

                if (focusCandidate == null) {
                    /* No candidate, take this one */
                    focusCandidate = view;
                    foundFullyContainedFocusable = viewIsFullyContained;
                } else {
                    final boolean viewIsCloserToBoundary =
                            (leftFocus && viewLeft < focusCandidate.getLeft()) ||
                                    (!leftFocus && viewRight > focusCandidate.getRight());

                    if (foundFullyContainedFocusable) {
                        if (viewIsFullyContained && viewIsCloserToBoundary) {
                            /*
                             * We're dealing with only fully contained views, so
                             * it has to be closer to the boundary to beat our
                             * candidate
                             */
                            focusCandidate = view;
                        }
                    } else {
                        if (viewIsFullyContained) {
                            /* Any fully contained view beats a partially contained view */
                            focusCandidate = view;
                            foundFullyContainedFocusable = true;
                        } else if (viewIsCloserToBoundary) {
                            /*
                             * Partially contained view beats another partially
                             * contained view if it's closer
                             */
                            focusCandidate = view;
                        }
                    }
                }
            }
        }

        return focusCandidate;
    }

    /**
     * <p>Handles scrolling in response to a "page up/down" shortcut press. This
     * method will scroll the view by one page left or right and give the focus
     * to the leftmost/rightmost component in the new visible area. If no
     * component is a good candidate for focus, this scrollview reclaims the
     * focus.</p>
     *
     * @param direction the scroll direction: {@link android.view.View#FOCUS_LEFT}
     *                  to go one page left or {@link android.view.View#FOCUS_RIGHT}
     *                  to go one page right
     * @return true if the key event is consumed by this method, false otherwise
     */
    public boolean pageScroll(int direction) {
        boolean right = direction == View.FOCUS_RIGHT;
        int width = getWidth();

        if (right) {
            mTempRect.left = getScrollX() + width;
            int count = getChildCount();
            if (count > 0) {
                View view = getChildAt(0);
                if (mTempRect.left + width > view.getRight()) {
                    mTempRect.left = view.getRight() - width;
                }
            }
        } else {
            mTempRect.left = getScrollX() - width;
            if (mTempRect.left < 0) {
                mTempRect.left = 0;
            }
        }
        mTempRect.right = mTempRect.left + width;

        return scrollAndFocus(direction, mTempRect.left, mTempRect.right);
    }

    /**
     * <p>Handles scrolling in response to a "home/end" shortcut press. This
     * method will scroll the view to the left or right and give the focus
     * to the leftmost/rightmost component in the new visible area. If no
     * component is a good candidate for focus, this scrollview reclaims the
     * focus.</p>
     *
     * @param direction the scroll direction: {@link android.view.View#FOCUS_LEFT}
     *                  to go the left of the view or {@link android.view.View#FOCUS_RIGHT}
     *                  to go the right
     * @return true if the key event is consumed by this method, false otherwise
     */
    public boolean fullScroll(int direction) {
        boolean right = direction == View.FOCUS_RIGHT;
        int width = getWidth();

        mTempRect.left = 0;
        mTempRect.right = width;

        if (right) {
            int count = getChildCount();
            if (count > 0) {
                View view = getChildAt(0);
                mTempRect.right = view.getRight();
                mTempRect.left = mTempRect.right - width;
            }
        }

        return scrollAndFocus(direction, mTempRect.left, mTempRect.right);
    }

    /**
     * <p>Scrolls the view to make the area defined by left and
     * <code>right visible. This method attempts to give the focus
     * to a component visible in this area. If no component can be focused in
     * the new visible area, the focus is reclaimed by this scrollview.</p>
     *
     * @param direction the scroll direction: {@link android.view.View#FOCUS_LEFT}
     *                  to go left {@link android.view.View#FOCUS_RIGHT} to right
     * @param left     the left offset of the new area to be made visible
     * @param right    the right offset of the new area to be made visible
     * @return true if the key event is consumed by this method, false otherwise
     */
    private boolean scrollAndFocus(int direction, int left, int right) {
        boolean handled = true;

        int width = getWidth();
        int containerLeft = getScrollX();
        int containerRight = containerLeft + width;
        boolean goLeft = direction == View.FOCUS_LEFT;

        View newFocused = findFocusableViewInBounds(goLeft, left, right);
        if (newFocused == null) {
            newFocused = this;
        }

        if (left >= containerLeft && right <= containerRight) {
            handled = false;
        } else {
            int delta = goLeft ? (left - containerLeft) : (right - containerRight);
            doScrollX(delta);
        }

        if (newFocused != findFocus() && newFocused.requestFocus(direction)) {
            mScrollViewMovedFocus = true;
            mScrollViewMovedFocus = false;
        }

        return handled;
    }

    /**
     * Handle scrolling in response to a left or right arrow click.
     *
     * @param direction The direction corresponding to the arrow key that was
     *                  pressed
     * @return True if we consumed the event, false otherwise
     */
    public boolean arrowScroll(int direction) {

        View currentFocused = findFocus();
        if (currentFocused == this) currentFocused = null;

        View nextFocused = FocusFinder.getInstance().findNextFocus(this, currentFocused, direction);

        final int maxJump = getMaxScrollAmount();

        if (nextFocused != null && isWithinDeltaOfScreen(nextFocused, maxJump)) {
            nextFocused.getDrawingRect(mTempRect);
            offsetDescendantRectToMyCoords(nextFocused, mTempRect);
            int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
            doScrollX(scrollDelta);
            nextFocused.requestFocus(direction);
        } else {
            // no new focus
            int scrollDelta = maxJump;

            if (direction == View.FOCUS_LEFT && getScrollX() < scrollDelta) {
                scrollDelta = getScrollX();
            } else if (direction == View.FOCUS_RIGHT && getChildCount() > 0) {
                
                int daRight = getChildAt(0).getRight();

                int screenRight = getScrollX() + getWidth();

                if (daRight - screenRight < maxJump) {
                    scrollDelta = daRight - screenRight;
                }
            }
            if (scrollDelta == 0) {
                return false;
            }
            doScrollX(direction == View.FOCUS_RIGHT ? scrollDelta : -scrollDelta);
        }

        if (currentFocused != null && currentFocused.isFocused()
                && isOffScreen(currentFocused)) {
            // previously focused item still has focus and is off screen, give
            // it up (take it back to ourselves)
            // (also, need to temporarily force FOCUS_BEFORE_DESCENDANTS so we are
            // sure to
            // get it)
            final int descendantFocusability = getDescendantFocusability();  // save
            setDescendantFocusability(ViewGroup.FOCUS_BEFORE_DESCENDANTS);
            requestFocus();
            setDescendantFocusability(descendantFocusability);  // restore
        }
        return true;
    }

    /**
     * @return whether the descendant of this scroll view is scrolled off
     *  screen.
     */
    private boolean isOffScreen(View descendant) {
        return !isWithinDeltaOfScreen(descendant, 0);
    }

    /**
     * @return whether the descendant of this scroll view is within delta
     *  pixels of being on the screen.
     */
    private boolean isWithinDeltaOfScreen(View descendant, int delta) {
        descendant.getDrawingRect(mTempRect);
        offsetDescendantRectToMyCoords(descendant, mTempRect);

        return (mTempRect.right + delta) >= getScrollX()
                && (mTempRect.left - delta) <= (getScrollX() + getWidth());
    }

    /**
     * Smooth scroll by a X delta
     *
     * @param delta the number of pixels to scroll by on the X axis
     */
    private void doScrollX(int delta) {
        if (delta != 0) {
            if (mSmoothScrollingEnabled) {
                smoothScrollBy(delta, 0);
            } else {
                scrollBy(delta, 0);
            }
        }
    }

    /**
     * Like {@link View#scrollBy}, but scroll smoothly instead of immediately.
     *
     * @param dx the number of pixels to scroll by on the X axis
     * @param dy the number of pixels to scroll by on the Y axis
     */
    public final void smoothScrollBy(int dx, int dy) {
        if (getChildCount() == 0) {
            // Nothing to do.
            return;
        }
        long duration = AnimationUtils.currentAnimationTimeMillis() - mLastScroll;
        if (duration > ANIMATED_SCROLL_GAP) {
            final int width = getWidth() - mPaddingRight - mPaddingLeft;
            final int right = getChildAt(0).getWidth();
            final int maxX = Math.max(0, right - width);
            final int scrollX = mScrollX;
            dx = Math.max(0, Math.min(scrollX + dx, maxX)) - scrollX;

            mScroller.startScroll(scrollX, mScrollY, dx, 0);
            invalidate();
        } else {
            if (!mScroller.isFinished()) {
                mScroller.abortAnimation();
            }
            scrollBy(dx, dy);
        }
        mLastScroll = AnimationUtils.currentAnimationTimeMillis();
    }

    /**
     * Like {@link #scrollTo}, but scroll smoothly instead of immediately.
     *
     * @param x the position where to scroll on the X axis
     * @param y the position where to scroll on the Y axis
     */
    public final void smoothScrollTo(int x, int y) {
        smoothScrollBy(x - mScrollX, y - mScrollY);
    }

    /**
     * <p>The scroll range of a scroll view is the overall width of all of its
     * children.</p>
     */
    @Override
    protected int computeHorizontalScrollRange() {
        final int count = getChildCount();
        final int contentWidth = getWidth() - mPaddingLeft - mPaddingRight;
        if (count == 0) {
            return contentWidth;
        }
        
        return getChildAt(0).getRight();
    }
    
    @Override
    protected int computeHorizontalScrollOffset() {
        return Math.max(0, super.computeHorizontalScrollOffset());
    }

    @Override
    protected void measureChild(View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec) {
        ViewGroup.LayoutParams lp = child.getLayoutParams();

        int childWidthMeasureSpec;
        int childHeightMeasureSpec;

        childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec, mPaddingTop
                + mPaddingBottom, lp.height);

        childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);

        child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
    }

    @Override
    protected void measureChildWithMargins(View child, int parentWidthMeasureSpec, int widthUsed,
            int parentHeightMeasureSpec, int heightUsed) {
        final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();

        final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec,
                mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin
                        + heightUsed, lp.height);
        final int childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(
                lp.leftMargin + lp.rightMargin, MeasureSpec.UNSPECIFIED);

        child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
    }

    @Override
    public void computeScroll() {
        if (mScroller.computeScrollOffset()) {
            // This is called at drawing time by ViewGroup.  We don't want to
            // re-show the scrollbars at this point, which scrollTo will do,
            // so we replicate most of scrollTo here.
            //
            //         It's a little odd to call onScrollChanged from inside the drawing.
            //
            //         It is, except when you remember that computeScroll() is used to
            //         animate scrolling. So unless we want to defer the onScrollChanged()
            //         until the end of the animated scrolling, we don't really have a
            //         choice here.
            //
            //         I agree.  The alternative, which I think would be worse, is to post
            //         something and tell the subclasses later.  This is bad because there
            //         will be a window where mScrollX/Y is different from what the app
            //         thinks it is.
            //
            int oldX = mScrollX;
            int oldY = mScrollY;
            int x = mScroller.getCurrX();
            int y = mScroller.getCurrY();

            if (getChildCount() > 0) {
                View child = getChildAt(0);
                x = clamp(x, getWidth() - mPaddingRight - mPaddingLeft, child.getWidth());
                y = clamp(y, getHeight() - mPaddingBottom - mPaddingTop, child.getHeight());
                if (x != oldX || y != oldY) {
                    mScrollX = x;
                    mScrollY = y;
                    onScrollChanged(x, y, oldX, oldY);
                }
            }
            awakenScrollBars();

            // Keep on drawing until the animation has finished.
            postInvalidate();
        }
    }

    /**
     * Scrolls the view to the given child.
     *
     * @param child the View to scroll to
     */
    private void scrollToChild(View child) {
        child.getDrawingRect(mTempRect);

        /* Offset from child's local coordinates to ScrollView coordinates */
        offsetDescendantRectToMyCoords(child, mTempRect);

        int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);

        if (scrollDelta != 0) {
            scrollBy(scrollDelta, 0);
        }
    }

    /**
     * If rect is off screen, scroll just enough to get it (or at least the
     * first screen size chunk of it) on screen.
     *
     * @param rect      The rectangle.
     * @param immediate True to scroll immediately without animation
     * @return true if scrolling was performed
     */
    private boolean scrollToChildRect(Rect rect, boolean immediate) {
        final int delta = computeScrollDeltaToGetChildRectOnScreen(rect);
        final boolean scroll = delta != 0;
        if (scroll) {
            if (immediate) {
                scrollBy(delta, 0);
            } else {
                smoothScrollBy(delta, 0);
            }
        }
        return scroll;
    }

    /**
     * Compute the amount to scroll in the X direction in order to get
     * a rectangle completely on the screen (or, if taller than the screen,
     * at least the first screen size chunk of it).
     *
     * @param rect The rect.
     * @return The scroll delta.
     */
    protected int computeScrollDeltaToGetChildRectOnScreen(Rect rect) {
        if (getChildCount() == 0) return 0;

        int width = getWidth();
        int screenLeft = getScrollX();
        int screenRight = screenLeft + width;

        int fadingEdge = getHorizontalFadingEdgeLength();

        // leave room for left fading edge as long as rect isn't at very left
        if (rect.left > 0) {
            screenLeft += fadingEdge;
        }

        // leave room for right fading edge as long as rect isn't at very right
        if (rect.right < getChildAt(0).getWidth()) {
            screenRight -= fadingEdge;
        }

        int scrollXDelta = 0;

        if (rect.right > screenRight && rect.left > screenLeft) {
            // need to move right to get it in view: move right just enough so
            // that the entire rectangle is in view (or at least the first
            // screen size chunk).

            if (rect.width() > width) {
                // just enough to get screen size chunk on
                scrollXDelta += (rect.left - screenLeft);
            } else {
                // get entire rect at right of screen
                scrollXDelta += (rect.right - screenRight);
            }

            // make sure we aren't scrolling beyond the end of our content
            int right = getChildAt(0).getRight();
            int distanceToRight = right - screenRight;
            scrollXDelta = Math.min(scrollXDelta, distanceToRight);

        } else if (rect.left < screenLeft && rect.right < screenRight) {
            // need to move right to get it in view: move right just enough so that
            // entire rectangle is in view (or at least the first screen
            // size chunk of it).

            if (rect.width() > width) {
                // screen size chunk
                scrollXDelta -= (screenRight - rect.right);
            } else {
                // entire rect at left
                scrollXDelta -= (screenLeft - rect.left);
            }

            // make sure we aren't scrolling any further than the left our content
            scrollXDelta = Math.max(scrollXDelta, -getScrollX());
        }
        return scrollXDelta;
    }

    @Override
    public void requestChildFocus(View child, View focused) {
        if (!mScrollViewMovedFocus) {
            if (!mIsLayoutDirty) {
                scrollToChild(focused);
            } else {
                // The child may not be laid out yet, we can't compute the scroll yet
                mChildToScrollTo = focused;
            }
        }
        super.requestChildFocus(child, focused);
    }


    /**
     * When looking for focus in children of a scroll view, need to be a little
     * more careful not to give focus to something that is scrolled off screen.
     *
     * This is more expensive than the default {@link android.view.ViewGroup}
     * implementation, otherwise this behavior might have been made the default.
     */
    @Override
    protected boolean onRequestFocusInDescendants(int direction,
            Rect previouslyFocusedRect) {

        // convert from forward / backward notation to up / down / left / right
        // (ugh).
        if (direction == View.FOCUS_FORWARD) {
            direction = View.FOCUS_RIGHT;
        } else if (direction == View.FOCUS_BACKWARD) {
            direction = View.FOCUS_LEFT;
        }

        final View nextFocus = previouslyFocusedRect == null ?
                FocusFinder.getInstance().findNextFocus(this, null, direction) :
                FocusFinder.getInstance().findNextFocusFromRect(this,
                        previouslyFocusedRect, direction);

        if (nextFocus == null) {
            return false;
        }

        if (isOffScreen(nextFocus)) {
            return false;
        }

        return nextFocus.requestFocus(direction, previouslyFocusedRect);
    }

    @Override
    public boolean requestChildRectangleOnScreen(View child, Rect rectangle,
            boolean immediate) {
        // offset into coordinate space of this scroll view
        rectangle.offset(child.getLeft() - child.getScrollX(),
                child.getTop() - child.getScrollY());

        return scrollToChildRect(rectangle, immediate);
    }

    @Override
    public void requestLayout() {
        mIsLayoutDirty = true;
        super.requestLayout();
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        mIsLayoutDirty = false;
        // Give a child focus if it needs it
        if (mChildToScrollTo != null && isViewDescendantOf(mChildToScrollTo, this)) {
                scrollToChild(mChildToScrollTo);
        }
        mChildToScrollTo = null;

        // Calling this with the present values causes it to re-clam them
        scrollTo(mScrollX, mScrollY);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        View currentFocused = findFocus();
        if (null == currentFocused || this == currentFocused)
            return;

        final int maxJump = mRight - mLeft;

        if (isWithinDeltaOfScreen(currentFocused, maxJump)) {
            currentFocused.getDrawingRect(mTempRect);
            offsetDescendantRectToMyCoords(currentFocused, mTempRect);
            int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
            doScrollX(scrollDelta);
        }
    }

    /**
     * Return true if child is an descendant of parent, (or equal to the parent).
     */
    private boolean isViewDescendantOf(View child, View parent) {
        if (child == parent) {
            return true;
        }

        final ViewParent theParent = child.getParent();
        return (theParent instanceof ViewGroup) && isViewDescendantOf((View) theParent, parent);
    }

    /**
     * Fling the scroll view
     *
     * @param velocityX The initial velocity in the X direction. Positive
     *                  numbers mean that the finger/curor is moving down the screen,
     *                  which means we want to scroll towards the left.
     */
    public void fling(int velocityX) {
        if (getChildCount() > 0) {
            int width = getWidth() - mPaddingRight - mPaddingLeft;
            int right = getChildAt(0).getWidth();
    
            mScroller.fling(mScrollX, mScrollY, velocityX, 0, 0, 
                    Math.max(0, right - width), 0, 0);
    
            final boolean movingRight = velocityX > 0;
    
            View newFocused = findFocusableViewInMyBounds(movingRight,
                    mScroller.getFinalX(), findFocus());
    
            if (newFocused == null) {
                newFocused = this;
            }
    
            if (newFocused != findFocus()
                    && newFocused.requestFocus(movingRight ? View.FOCUS_RIGHT : View.FOCUS_LEFT)) {
                mScrollViewMovedFocus = true;
                mScrollViewMovedFocus = false;
            }
    
            invalidate();
        }
    }

    /**
     * {@inheritDoc}
     *
     * <p>This version also clamps the scrolling to the bounds of our child.
     */
    public void scrollTo(int x, int y) {
        // we rely on the fact the View.scrollBy calls scrollTo.
        if (getChildCount() > 0) {
            View child = getChildAt(0);
            x = clamp(x, getWidth() - mPaddingRight - mPaddingLeft, child.getWidth());
            y = clamp(y, getHeight() - mPaddingBottom - mPaddingTop, child.getHeight());
            if (x != mScrollX || y != mScrollY) {
                super.scrollTo(x, y);
            }
        }
    }

    private int clamp(int n, int my, int child) {
        if (my >= child || n < 0) {
            return 0;
        }
        if ((my + n) > child) {
            return child - my;
        }
        return n;
    }
}