Android的边缘效应的相关类EdgeEffectCompat学习

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Android的边缘效应的相关类EdgeEffectCompat学习

Android中可以的ListView，ScrollView，RecyclerView等滑动到界面的边界的时候会出现一个半透明的颜色边
框。这个边框就是Android的边缘效果。主要是类EdgeEffect，EdgeEffectCompat管理。效果如下图

1，EdgeEffectCompat类的学习

源码学习：

/**     * 构造一个新的对象     *     * <p>Note: 对于不支持的版本，将会没有效果</p>     *     * @param 上下文     */    public EdgeEffectCompat(Context context) {        mEdgeEffect = IMPL.newEdgeEffect(context);    }    /**     * Set the size of this edge effect in pixels.     * 设置边框的大小像素     *     * @param width Effect width in pixels     * @param height Effect height in pixels     */    public void setSize(int width, int height) {        IMPL.setSize(mEdgeEffect, width, height);    }    /**     * Reports if this EdgeEffectCompat's animation is finished. If this method returns false     * after a call to {@link #draw(Canvas)} the host widget should schedule another     * drawing pass to continue the animation.     *     * 边缘的显示动画是否结束     *     * @return true if animation is finished, false if drawing should continue on the next frame.      *     */    public boolean isFinished() {        return IMPL.isFinished(mEdgeEffect);    }    /**     * Immediately finish the current animation.     * After this call {@link #isFinished()} will return true.     * 立刻结束显示动画     */    public void finish() {        IMPL.finish(mEdgeEffect);    }    /**     * 在处理滑动的时候调用     * A view should call this when content is pulled away from an edge by the user.     * This will update the state of the current visual effect and its associated animation.     * The host view should always {@link android.view.View#invalidate()} if this method     * returns true and draw the results accordingly.     *     * @param deltaDistance Change in distance since the last call. Values may be 0 (no change) to     *                      1.f (full length of the view) or negative values to express change     *                      back toward the edge reached to initiate the effect.     *                      范围：[-1,1]，是要移动的距里在View的边长的占比     * @param displacement  The displacement from the starting side of the effect of the point     *                      initiating the pull. In the case of touch this is the finger position.     *                      Values may be from 0-1.     *                      范围[0,1]，手指所在的位置在非移动边的位置占比     * @return true if the host view should call invalidate, false if it should not.     * 如果返回为true就表示会重新刷新View。     */    public boolean onPull(float deltaDistance, float displacement) {        return IMPL.onPull(mEdgeEffect, deltaDistance, displacement);    }   /**     * Call when the object is released after being pulled.     * This will begin the "decay" phase of the effect. After calling this method     * the host view should {@link android.view.View#invalidate()} if this method     * returns true and thereby draw the results accordingly.     * 是否被释放     * @return true if the host view should invalidate, false if it should not.     */    public boolean onRelease() {        return IMPL.onRelease(mEdgeEffect);    }    /**     * Call when the effect absorbs an impact at the given velocity.     * Used when a fling reaches the scroll boundary.     *      * 吸收一个速度，当到View的边界的时候会显示相应的动画     * <p>When using a {@link android.widget.Scroller} or {@link android.widget.OverScroller},     * the method <code>getCurrVelocity</code> will provide a reasonable approximation     * to use here.</p>     *     * @param velocity Velocity at impact in pixels per second.     * @return true if the host view should invalidate, false if it should not.     */    public boolean onAbsorb(int velocity) {        return IMPL.onAbsorb(mEdgeEffect, velocity);    }    /**     *  关键方法，在View的onDraw方法中调用会显示相应的动画，在调用这个方法之前要计算相应的     * 平移，旋转的量。     * Draw into the provided canvas. Assumes that the canvas has been rotated     * accordingly and the size has been set. The effect will be drawn the full     * width of X=0 to X=width, beginning from Y=0 and extending to some factor 小于     * 1.f of height.     *       * @param canvas Canvas to draw into     * @return true if drawing should continue beyond this frame to continue the     *         animation     */    public boolean draw(Canvas canvas) {        return IMPL.draw(mEdgeEffect, canvas);    }

EdgeEffectCompat实现原理：
EdgeEffcetCompat的实现就是在滑动控件滑动到边界的时候在边界画一个圆弧，然后根据
滑动的位置（滑动方向的偏移量，非滑动方向坐标的位置）进行缩放平移，同时进行动画的播放。
具体如下图（蓝色部分）：

2，EdgeEffectCompat类的应用

这里我用ScrollView的相关源码进行学习，展示EdgeEffectCompat是如何应用到View中的。
1. 在View的绘制过程中，通过EdgeEffectCompat.setSize(width,height)和EdgeEffectCompat.draw(canvas)两个方法来绘制效果图。相关的详细解释看注释：

    @Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        if (mTopEdgeEffect != null) {            final int width = getWidth() - getPaddingRight() - getPaddingLeft();//内容的宽度            final int scrollY = getScrollY();//当前滑动的量            if (!mTopEdgeEffect.isFinished()) {//动画是否已经结束                int restoreCount = canvas.save();                canvas.translate(getPaddingLeft(), Math.min(0, scrollY));//画布向右平移，如果View有向下超过0的偏移量就要再向上偏移，超过上边界的平移量                mTopEdgeEffect.setSize(width , getHeight());//设置效果的展示范围（内容的宽度，和View的高度）                if (mTopEdgeEffect.draw(canvas)) {//绘制边缘效果图，如果绘制需要进行动画效果返回true                    ViewCompat.postInvalidateOnAnimation(this);//进行动画                }                canvas.restoreToCount(restoreCount);            }            if (!mBottomEdgeEffect.isFinished()) {                int restoreCount = canvas.save();                //下面两行代码的作用就是把画布平移旋转到底部展示，并让效果向上显示                canvas.translate(getPaddingLeft() - width, Math.max(getScrollRange(), scrollY) + getHeight());                canvas.rotate(180, width, 0);                mBottomEdgeEffect.setSize(width, getHeight());                if (mBottomEdgeEffect.draw(canvas)) {                    ViewCompat.postInvalidateOnAnimation(this);                }                canvas.restoreToCount(restoreCount);            }        }    }

在View.onTouchEvent()方法中调用EdgeEffectCompat.onPull方法详细见源码：

    @Override    public boolean onTouchEvent(MotionEvent ev) {        final int actionMark = MotionEventCompat.getActionMasked(ev);        switch (actionMark) {            case MotionEvent.ACTION_MOVE:                final int pointIndex = ev.findPointerIndex(mActionPointerId);                if (pointIndex == -1) {                    break;                }                final int y = (int) ev.getY(pointIndex);                int deltaY = mLastPointY - y;                if (!mIsBeingDragged && Math.abs(deltaY) > mTouchSlop) {                    ViewParent parent = getParent();                    if (parent != null) {                        parent.requestDisallowInterceptTouchEvent(true);                    }                    if (deltaY > 0) {//减去积累的量                        deltaY -= mTouchSlop;                    } else {                        deltaY += mTouchSlop;                    }                    mIsBeingDragged = true;                }                if (mIsBeingDragged) {                    final int oldY = getScrollY();                    final int range = getScrollRange();                    final int overMode = getOverScrollMode();                    boolean canOverScroll = overMode == View.OVER_SCROLL_ALWAYS                            || (overMode == View.OVER_SCROLL_IF_CONTENT_SCROLLS && range > 0);                   //主要的代码                    if (canOverScroll) {                        // 边缘效果                        ensureGlows();                        final int pullToY = oldY + deltaY;                        if (pullToY < 0) {//在顶部                            mTopEdgeEffect.onPull((float) deltaY / getHeight(), ev.getX(pointIndex) / getWidth());                            if (!mBottomEdgeEffect.isFinished()) {                                mBottomEdgeEffect.onRelease();                            }                        } else if (pullToY > range) {//在底部                            mBottomEdgeEffect.onPull((float) deltaY / getHeight(), 1.0f - ev.getX(pointIndex) / getWidth());                            if (!mTopEdgeEffect.isFinished()) {                                mTopEdgeEffect.onRelease();                            }                        }                        if (mTopEdgeEffect != null && (!mTopEdgeEffect.isFinished() || !mBottomEdgeEffect.isFinished())) {                            ViewCompat.postInvalidateOnAnimation(this);                        }                    }                    mLastPointY = y;                }                break;            case MotionEvent.ACTION_CANCEL:                if (mTopEdgeEffect != null) {                    mTopEdgeEffect.onRelease();                    mBottomEdgeEffect.onRelease();                }                break;            case MotionEvent.ACTION_UP:                if (mTopEdgeEffect != null) {                    mTopEdgeEffect.onRelease();                    mBottomEdgeEffect.onRelease();                }                break;        }        return true;    }    private void ensureGlows() {        if (getOverScrollMode() != OVER_SCROLL_NEVER) {            Context context = getContext();            if (context != null && mTopEdgeEffect == null) {                mTopEdgeEffect = new EdgeEffectCompat(context);                mBottomEdgeEffect = new EdgeEffectCompat(context);            }        } else {            mTopEdgeEffect = null;            mBottomEdgeEffect = null;        }    }

在快速滑动View的时候，View会有一定的速度到达边界，这时候就要根据到达边界的速度进行显示。
一般View是用Scroller来进行Fling动画效果的。这时候就要在View.computeScroll方法中设置。详细如下：

    @Override    public void computeScroll() {        if (mScroller.computeScrollOffset()) {            int oldX = getScrollX();            int oldY = getScrollY();            int newX = mScroller.getCurrX();            int newY = mScroller.getCurrY();//            Log.i(TAG, "computeScroll: oldY : " + oldY +" newY : "+newY);            if (oldX != newX || oldY != newY) {                final int range = getScrollRange();                final int overMode = getOverScrollMode();                boolean canOverScroll = overMode == View.OVER_SCROLL_ALWAYS                        || (overMode == View.OVER_SCROLL_IF_CONTENT_SCROLLS && range > 0);                overScrollByCompat(newX - oldX, newY - oldY, oldX, oldY, 0, range, 0, 0);                if (canOverScroll) {//这部分是吓死边缘效果的                    ensureGlows();                    if (newY < 0 && oldY > 0) {//到达顶部，吸收速度                        mTopEdgeEffect.onAbsorb((int) mScroller.getCurrVelocity());                    } else if (newY > range && oldY < range) {//到达底部，吸收速度                        mBottomEdgeEffect.onAbsorb((int) mScroller.getCurrVelocity());                    }                }            }        }    }

Android的边缘效应的相关类EdgeEffectCompat学习就到这里。

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