Android example source code file (FastScroller.java)

This example Android source code file (FastScroller.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

alpha_max, android, baseadapter, content, drawable, drawing, expandablelistview, graphics, handler, object, paint, rectf, scrollfade, sectionindexer, state_dragging, state_exit, state_none, state_visible, string, ui

The FastScroller.java Android example source code

/*
 * Copyright (C) 2008 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.ColorStateList;
import android.content.res.Resources;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.RectF;
import android.graphics.drawable.Drawable;
import android.os.Handler;
import android.os.SystemClock;
import android.util.TypedValue;
import android.view.MotionEvent;
import android.widget.AbsListView.OnScrollListener;

/**
 * Helper class for AbsListView to draw and control the Fast Scroll thumb
 */
class FastScroller {
   
    // Minimum number of pages to justify showing a fast scroll thumb
    private static int MIN_PAGES = 4;
    // Scroll thumb not showing
    private static final int STATE_NONE = 0;
    // Not implemented yet - fade-in transition
    private static final int STATE_ENTER = 1;
    // Scroll thumb visible and moving along with the scrollbar
    private static final int STATE_VISIBLE = 2;
    // Scroll thumb being dragged by user
    private static final int STATE_DRAGGING = 3;
    // Scroll thumb fading out due to inactivity timeout
    private static final int STATE_EXIT = 4;
    
    private Drawable mThumbDrawable;
    private Drawable mOverlayDrawable;

    private int mThumbH;
    private int mThumbW;
    private int mThumbY;

    private RectF mOverlayPos;
    private int mOverlaySize;

    private AbsListView mList;
    private boolean mScrollCompleted;
    private int mVisibleItem;
    private Paint mPaint;
    private int mListOffset;
    private int mItemCount = -1;
    private boolean mLongList;
    
    private Object [] mSections;
    private String mSectionText;
    private boolean mDrawOverlay;
    private ScrollFade mScrollFade;
    
    private int mState;
    
    private Handler mHandler = new Handler();
    
    private BaseAdapter mListAdapter;
    private SectionIndexer mSectionIndexer;

    private boolean mChangedBounds;
    
    public FastScroller(Context context, AbsListView listView) {
        mList = listView;
        init(context);
    }

    public void setState(int state) {
        switch (state) {
            case STATE_NONE:
                mHandler.removeCallbacks(mScrollFade);
                mList.invalidate();
                break;
            case STATE_VISIBLE:
                if (mState != STATE_VISIBLE) { // Optimization
                    resetThumbPos();
                }
                // Fall through
            case STATE_DRAGGING:
                mHandler.removeCallbacks(mScrollFade);
                break;
            case STATE_EXIT:
                int viewWidth = mList.getWidth();
                mList.invalidate(viewWidth - mThumbW, mThumbY, viewWidth, mThumbY + mThumbH);
                break;
        }
        mState = state;
    }
    
    public int getState() {
        return mState;
    }
    
    private void resetThumbPos() {
        final int viewWidth = mList.getWidth();
        // Bounds are always top right. Y coordinate get's translated during draw
        mThumbDrawable.setBounds(viewWidth - mThumbW, 0, viewWidth, mThumbH);
        mThumbDrawable.setAlpha(ScrollFade.ALPHA_MAX);
    }
    
    private void useThumbDrawable(Context context, Drawable drawable) {
        mThumbDrawable = drawable;
        mThumbW = context.getResources().getDimensionPixelSize(
                com.android.internal.R.dimen.fastscroll_thumb_width);
        mThumbH = context.getResources().getDimensionPixelSize(
                com.android.internal.R.dimen.fastscroll_thumb_height);
        mChangedBounds = true;
    }

    private void init(Context context) {
        // Get both the scrollbar states drawables
        final Resources res = context.getResources();
        useThumbDrawable(context, res.getDrawable(
                com.android.internal.R.drawable.scrollbar_handle_accelerated_anim2));
        
        mOverlayDrawable = res.getDrawable(
                com.android.internal.R.drawable.menu_submenu_background);
        
        mScrollCompleted = true;

        getSectionsFromIndexer();

        mOverlaySize = context.getResources().getDimensionPixelSize(
                com.android.internal.R.dimen.fastscroll_overlay_size);
        mOverlayPos = new RectF();
        mScrollFade = new ScrollFade();
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setTextAlign(Paint.Align.CENTER);
        mPaint.setTextSize(mOverlaySize / 2);
        TypedArray ta = context.getTheme().obtainStyledAttributes(new int[] { 
                android.R.attr.textColorPrimary });
        ColorStateList textColor = ta.getColorStateList(ta.getIndex(0));
        int textColorNormal = textColor.getDefaultColor();
        mPaint.setColor(textColorNormal);
        mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
        
        mState = STATE_NONE;
    }
    
    void stop() {
        setState(STATE_NONE);
    }
    
    boolean isVisible() {
        return !(mState == STATE_NONE);
    }
    
    public void draw(Canvas canvas) {
        
        if (mState == STATE_NONE) {
            // No need to draw anything
            return;
        }

        final int y = mThumbY;
        final int viewWidth = mList.getWidth();
        final FastScroller.ScrollFade scrollFade = mScrollFade;

        int alpha = -1;
        if (mState == STATE_EXIT) {
            alpha = scrollFade.getAlpha();
            if (alpha < ScrollFade.ALPHA_MAX / 2) {
                mThumbDrawable.setAlpha(alpha * 2);
            }
            int left = viewWidth - (mThumbW * alpha) / ScrollFade.ALPHA_MAX;
            mThumbDrawable.setBounds(left, 0, viewWidth, mThumbH);
            mChangedBounds = true;
        }

        canvas.translate(0, y);
        mThumbDrawable.draw(canvas);
        canvas.translate(0, -y);

        // If user is dragging the scroll bar, draw the alphabet overlay
        if (mState == STATE_DRAGGING && mDrawOverlay) {
            mOverlayDrawable.draw(canvas);
            final Paint paint = mPaint;
            float descent = paint.descent();
            final RectF rectF = mOverlayPos;
            canvas.drawText(mSectionText, (int) (rectF.left + rectF.right) / 2,
                    (int) (rectF.bottom + rectF.top) / 2 + mOverlaySize / 4 - descent, paint);
        } else if (mState == STATE_EXIT) {
            if (alpha == 0) { // Done with exit
                setState(STATE_NONE);
            } else {
                mList.invalidate(viewWidth - mThumbW, y, viewWidth, y + mThumbH);            
            }
        }
    }

    void onSizeChanged(int w, int h, int oldw, int oldh) {
        if (mThumbDrawable != null) {
            mThumbDrawable.setBounds(w - mThumbW, 0, w, mThumbH);
        }
        final RectF pos = mOverlayPos;
        pos.left = (w - mOverlaySize) / 2;
        pos.right = pos.left + mOverlaySize;
        pos.top = h / 10; // 10% from top
        pos.bottom = pos.top + mOverlaySize;
        if (mOverlayDrawable != null) {
            mOverlayDrawable.setBounds((int) pos.left, (int) pos.top,
                (int) pos.right, (int) pos.bottom);
        }
    }
    
    void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, 
            int totalItemCount) {
        // Are there enough pages to require fast scroll? Recompute only if total count changes
        if (mItemCount != totalItemCount && visibleItemCount > 0) {
            mItemCount = totalItemCount;
            mLongList = mItemCount / visibleItemCount >= MIN_PAGES;
        }
        if (!mLongList) {
            if (mState != STATE_NONE) {
                setState(STATE_NONE);
            }
            return;
        }
        if (totalItemCount - visibleItemCount > 0 && mState != STATE_DRAGGING ) {
            mThumbY = ((mList.getHeight() - mThumbH) * firstVisibleItem) 
                    / (totalItemCount - visibleItemCount);
            if (mChangedBounds) {
                resetThumbPos();
                mChangedBounds = false;
            }
        }
        mScrollCompleted = true;
        if (firstVisibleItem == mVisibleItem) {
            return;
        }
        mVisibleItem = firstVisibleItem;
        if (mState != STATE_DRAGGING) {
            setState(STATE_VISIBLE);
            mHandler.postDelayed(mScrollFade, 1500);
        }
    }

    SectionIndexer getSectionIndexer() {
        return mSectionIndexer;
    }

    Object[] getSections() {
        if (mListAdapter == null && mList != null) {
            getSectionsFromIndexer();
        }
        return mSections;
    }

    private void getSectionsFromIndexer() {
        Adapter adapter = mList.getAdapter();
        mSectionIndexer = null;
        if (adapter instanceof HeaderViewListAdapter) {
            mListOffset = ((HeaderViewListAdapter)adapter).getHeadersCount();
            adapter = ((HeaderViewListAdapter)adapter).getWrappedAdapter();
        }
        if (adapter instanceof ExpandableListConnector) {
            ExpandableListAdapter expAdapter = ((ExpandableListConnector)adapter).getAdapter();
            if (expAdapter instanceof SectionIndexer) {
                mSectionIndexer = (SectionIndexer) expAdapter;
                mListAdapter = (BaseAdapter) adapter;
                mSections = mSectionIndexer.getSections();
            }
        } else {
            if (adapter instanceof SectionIndexer) {
                mListAdapter = (BaseAdapter) adapter;
                mSectionIndexer = (SectionIndexer) adapter;
                mSections = mSectionIndexer.getSections();
                
            } else {
                mListAdapter = (BaseAdapter) adapter;
                mSections = new String[] { " " };
            }
        }
    }

    private void scrollTo(float position) {
        int count = mList.getCount();
        mScrollCompleted = false;
        float fThreshold = (1.0f / count) / 8;
        final Object[] sections = mSections;
        int sectionIndex;
        if (sections != null && sections.length > 1) {
            final int nSections = sections.length;
            int section = (int) (position * nSections);
            if (section >= nSections) {
                section = nSections - 1;
            }
            int exactSection = section;
            sectionIndex = section;
            int index = mSectionIndexer.getPositionForSection(section);
            // Given the expected section and index, the following code will
            // try to account for missing sections (no names starting with..)
            // It will compute the scroll space of surrounding empty sections
            // and interpolate the currently visible letter's range across the
            // available space, so that there is always some list movement while
            // the user moves the thumb.
            int nextIndex = count;
            int prevIndex = index;
            int prevSection = section;
            int nextSection = section + 1;
            // Assume the next section is unique
            if (section < nSections - 1) {
                nextIndex = mSectionIndexer.getPositionForSection(section + 1);
            }
            
            // Find the previous index if we're slicing the previous section
            if (nextIndex == index) {
                // Non-existent letter
                while (section > 0) {
                    section--;
                    prevIndex = mSectionIndexer.getPositionForSection(section);
                    if (prevIndex != index) {
                        prevSection = section;
                        sectionIndex = section;
                        break;
                    } else if (section == 0) {
                        // When section reaches 0 here, sectionIndex must follow it.
                        // Assuming mSectionIndexer.getPositionForSection(0) == 0.
                        sectionIndex = 0;
                        break;
                    }
                }
            }
            // Find the next index, in case the assumed next index is not
            // unique. For instance, if there is no P, then request for P's 
            // position actually returns Q's. So we need to look ahead to make
            // sure that there is really a Q at Q's position. If not, move 
            // further down...
            int nextNextSection = nextSection + 1;
            while (nextNextSection < nSections &&
                    mSectionIndexer.getPositionForSection(nextNextSection) == nextIndex) {
                nextNextSection++;
                nextSection++;
            }
            // Compute the beginning and ending scroll range percentage of the
            // currently visible letter. This could be equal to or greater than
            // (1 / nSections). 
            float fPrev = (float) prevSection / nSections;
            float fNext = (float) nextSection / nSections;
            if (prevSection == exactSection && position - fPrev < fThreshold) {
                index = prevIndex;
            } else {
                index = prevIndex + (int) ((nextIndex - prevIndex) * (position - fPrev) 
                    / (fNext - fPrev));
            }
            // Don't overflow
            if (index > count - 1) index = count - 1;
            
            if (mList instanceof ExpandableListView) {
                ExpandableListView expList = (ExpandableListView) mList;
                expList.setSelectionFromTop(expList.getFlatListPosition(
                        ExpandableListView.getPackedPositionForGroup(index + mListOffset)), 0);
            } else if (mList instanceof ListView) {
                ((ListView)mList).setSelectionFromTop(index + mListOffset, 0);
            } else {
                mList.setSelection(index + mListOffset);
            }
        } else {
            int index = (int) (position * count);
            if (mList instanceof ExpandableListView) {
                ExpandableListView expList = (ExpandableListView) mList;
                expList.setSelectionFromTop(expList.getFlatListPosition(
                        ExpandableListView.getPackedPositionForGroup(index + mListOffset)), 0);
            } else if (mList instanceof ListView) {
                ((ListView)mList).setSelectionFromTop(index + mListOffset, 0);
            } else {
                mList.setSelection(index + mListOffset);
            }
            sectionIndex = -1;
        }

        if (sectionIndex >= 0) {
            String text = mSectionText = sections[sectionIndex].toString();
            mDrawOverlay = (text.length() != 1 || text.charAt(0) != ' ') &&
                    sectionIndex < sections.length;
        } else {
            mDrawOverlay = false;
        }
    }

    private void cancelFling() {
        // Cancel the list fling
        MotionEvent cancelFling = MotionEvent.obtain(0, 0, MotionEvent.ACTION_CANCEL, 0, 0, 0);
        mList.onTouchEvent(cancelFling);
        cancelFling.recycle();
    }
    
    boolean onInterceptTouchEvent(MotionEvent ev) {
        if (mState > STATE_NONE && ev.getAction() == MotionEvent.ACTION_DOWN) {
            if (isPointInside(ev.getX(), ev.getY())) {
                setState(STATE_DRAGGING);
                return true;
            }
        }
        return false;
    }

    boolean onTouchEvent(MotionEvent me) {
        if (mState == STATE_NONE) {
            return false;
        }

        final int action = me.getAction();

        if (action == MotionEvent.ACTION_DOWN) {
            if (isPointInside(me.getX(), me.getY())) {
                setState(STATE_DRAGGING);
                if (mListAdapter == null && mList != null) {
                    getSectionsFromIndexer();
                }
                if (mList != null) {
                    mList.requestDisallowInterceptTouchEvent(true);
                    mList.reportScrollStateChange(OnScrollListener.SCROLL_STATE_TOUCH_SCROLL);
                }

                cancelFling();
                return true;
            }
        } else if (action == MotionEvent.ACTION_UP) { // don't add ACTION_CANCEL here
            if (mState == STATE_DRAGGING) {
                if (mList != null) {
                    // ViewGroup does the right thing already, but there might
                    // be other classes that don't properly reset on touch-up,
                    // so do this explicitly just in case.
                    mList.requestDisallowInterceptTouchEvent(false);
                    mList.reportScrollStateChange(OnScrollListener.SCROLL_STATE_IDLE);
                }
                setState(STATE_VISIBLE);
                final Handler handler = mHandler;
                handler.removeCallbacks(mScrollFade);
                handler.postDelayed(mScrollFade, 1000);
                return true;
            }
        } else if (action == MotionEvent.ACTION_MOVE) {
            if (mState == STATE_DRAGGING) {
                final int viewHeight = mList.getHeight();
                // Jitter
                int newThumbY = (int) me.getY() - mThumbH + 10;
                if (newThumbY < 0) {
                    newThumbY = 0;
                } else if (newThumbY + mThumbH > viewHeight) {
                    newThumbY = viewHeight - mThumbH;
                }
                if (Math.abs(mThumbY - newThumbY) < 2) {
                    return true;
                }
                mThumbY = newThumbY;
                // If the previous scrollTo is still pending
                if (mScrollCompleted) {
                    scrollTo((float) mThumbY / (viewHeight - mThumbH));
                }
                return true;
            }
        }
        return false;
    }

    boolean isPointInside(float x, float y) {
        return x > mList.getWidth() - mThumbW && y >= mThumbY && y <= mThumbY + mThumbH;
    }

    public class ScrollFade implements Runnable {
        
        long mStartTime;
        long mFadeDuration;
        static final int ALPHA_MAX = 208;
        static final long FADE_DURATION = 200;
        
        void startFade() {
            mFadeDuration = FADE_DURATION;
            mStartTime = SystemClock.uptimeMillis();
            setState(STATE_EXIT);
        }
        
        int getAlpha() {
            if (getState() != STATE_EXIT) {
                return ALPHA_MAX;
            }
            int alpha;
            long now = SystemClock.uptimeMillis();
            if (now > mStartTime + mFadeDuration) {
                alpha = 0;
            } else {
                alpha = (int) (ALPHA_MAX - ((now - mStartTime) * ALPHA_MAX) / mFadeDuration); 
            }
            return alpha;
        }
        
        public void run() {
            if (getState() != STATE_EXIT) {
                startFade();
                return;
            }
            
            if (getAlpha() > 0) {
                mList.invalidate();
            } else {
                setState(STATE_NONE);
            }
        }
    }
}