Android example source code file (ScrollBarDrawable.java)

This example Android source code file (ScrollBarDrawable.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, drawable, drawing, graphics, override, paint, rect, scrollbardrawable, string, ui

The ScrollBarDrawable.java Android example source code

/*
 * Copyright (C) 2006 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.graphics.Canvas;
import android.graphics.ColorFilter;
import android.graphics.PixelFormat;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;

/**
 * This is only used by View for displaying its scroll bars.  It should probably
 * be moved in to the view package since it is used in that lower-level layer.
 * For now, we'll hide it so it can be cleaned up later.
 * {@hide}
 */
public class ScrollBarDrawable extends Drawable {
    private Drawable mVerticalTrack;
    private Drawable mHorizontalTrack;
    private Drawable mVerticalThumb;
    private Drawable mHorizontalThumb;
    private int mRange;
    private int mOffset;
    private int mExtent;
    private boolean mVertical;
    private boolean mChanged;
    private boolean mRangeChanged;
    private final Rect mTempBounds = new Rect();
    private boolean mAlwaysDrawHorizontalTrack;
    private boolean mAlwaysDrawVerticalTrack;

    public ScrollBarDrawable() {
    }

    /**
     * Indicate whether the horizontal scrollbar track should always be drawn regardless of the
     * extent. Defaults to false.
     *
     * @param alwaysDrawTrack Set to true if the track should always be drawn
     */
    public void setAlwaysDrawHorizontalTrack(boolean alwaysDrawTrack) {
        mAlwaysDrawHorizontalTrack = alwaysDrawTrack;
    }

    /**
     * Indicate whether the vertical scrollbar track should always be drawn regardless of the
     * extent. Defaults to false.
     *
     * @param alwaysDrawTrack Set to true if the track should always be drawn
     */
    public void setAlwaysDrawVerticalTrack(boolean alwaysDrawTrack) {
        mAlwaysDrawVerticalTrack = alwaysDrawTrack;
    }

    /**
     * Indicates whether the vertical scrollbar track should always be drawn regardless of the
     * extent.
     */
    public boolean getAlwaysDrawVerticalTrack() {
        return mAlwaysDrawVerticalTrack;
    }

    /**
     * Indicates whether the horizontal scrollbar track should always be drawn regardless of the
     * extent.
     */
    public boolean getAlwaysDrawHorizontalTrack() {
        return mAlwaysDrawHorizontalTrack;
    }

    public void setParameters(int range, int offset, int extent, boolean vertical) {
        if (mVertical != vertical) {
            mChanged = true;
        }

        if (mRange != range || mOffset != offset || mExtent != extent) {
            mRangeChanged = true;
        }

        mRange = range;
        mOffset = offset;
        mExtent = extent;
        mVertical = vertical;
    }

    @Override
    public void draw(Canvas canvas) {
        final boolean vertical = mVertical;
        final int extent = mExtent;
        final int range = mRange;

        boolean drawTrack = true;
        boolean drawThumb = true;
        if (extent <= 0 || range <= extent) {
            drawTrack = vertical ? mAlwaysDrawVerticalTrack : mAlwaysDrawHorizontalTrack;
            drawThumb = false;
        }

        Rect r = getBounds();
        if (canvas.quickReject(r.left, r.top, r.right, r.bottom, 
                Canvas.EdgeType.AA)) {
            return;
        }
        if (drawTrack) {
            drawTrack(canvas, r, vertical);
        }

        if (drawThumb) {
            int size = vertical ? r.height() : r.width();
            int thickness = vertical ? r.width() : r.height();
            int length = Math.round((float) size * extent / range);
            int offset = Math.round((float) (size - length) * mOffset / (range - extent));

            // avoid the tiny thumb
            int minLength = thickness * 2;
            if (length < minLength) {
                length = minLength;
            }
            // avoid the too-big thumb
            if (offset + length > size) {
                offset = size - length;
            }

            drawThumb(canvas, r, offset, length, vertical);
        }
    }

    @Override
    protected void onBoundsChange(Rect bounds) {
        super.onBoundsChange(bounds);
        mChanged = true;
    }

    protected void drawTrack(Canvas canvas, Rect bounds, boolean vertical) {
        Drawable track;
        if (vertical) {
            track = mVerticalTrack;
        } else {
            track = mHorizontalTrack;
        }
        if (track != null) {
            if (mChanged) {
                track.setBounds(bounds);
            }
            track.draw(canvas);
        }
    }

    protected void drawThumb(Canvas canvas, Rect bounds, int offset, int length, boolean vertical) {
        final Rect thumbRect = mTempBounds;
        final boolean changed = mRangeChanged || mChanged;
        if (changed) {
            if (vertical) {
                thumbRect.set(bounds.left,  bounds.top + offset,
                        bounds.right, bounds.top + offset + length);
            } else {
                thumbRect.set(bounds.left + offset, bounds.top,
                        bounds.left + offset + length, bounds.bottom);
            }
        }

        if (vertical) {
            final Drawable thumb = mVerticalThumb;
            if (changed) thumb.setBounds(thumbRect);
            thumb.draw(canvas);
        } else {
            final Drawable thumb = mHorizontalThumb;
            if (changed) thumb.setBounds(thumbRect);
            thumb.draw(canvas);
        }
    }

    public void setVerticalThumbDrawable(Drawable thumb) {
        if (thumb != null) {
            mVerticalThumb = thumb;
        }
    }

    public void setVerticalTrackDrawable(Drawable track) {
        mVerticalTrack = track;
    }

    public void setHorizontalThumbDrawable(Drawable thumb) {
        if (thumb != null) {
            mHorizontalThumb = thumb;
        }
    }

    public void setHorizontalTrackDrawable(Drawable track) {
        mHorizontalTrack = track;
    }

    public int getSize(boolean vertical) {
        if (vertical) {
            return (mVerticalTrack != null ?
                    mVerticalTrack : mVerticalThumb).getIntrinsicWidth();
        } else {
            return (mHorizontalTrack != null ?
                    mHorizontalTrack : mHorizontalThumb).getIntrinsicHeight();
        }
    }

    @Override
    public void setAlpha(int alpha) {
        if (mVerticalTrack != null) {
            mVerticalTrack.setAlpha(alpha);
        }
        mVerticalThumb.setAlpha(alpha);
        if (mHorizontalTrack != null) {
            mHorizontalTrack.setAlpha(alpha);
        }
        mHorizontalThumb.setAlpha(alpha);
    }

    @Override
    public void setColorFilter(ColorFilter cf) {
        if (mVerticalTrack != null) {
            mVerticalTrack.setColorFilter(cf);
        }
        mVerticalThumb.setColorFilter(cf);
        if (mHorizontalTrack != null) {
            mHorizontalTrack.setColorFilter(cf);
        }
        mHorizontalThumb.setColorFilter(cf);
    }

    @Override
    public int getOpacity() {
        return PixelFormat.TRANSLUCENT;
    }

    @Override
    public String toString() {
        return "ScrollBarDrawable: range=" + mRange + " offset=" + mOffset +
               " extent=" + mExtent + (mVertical ? " V" : " H");
    }
}