自定义视图绘制边缘滑动的效果

drawEdgeEffects

http://developer.android.com/training/gestures/viewgroup.html
InteractiveChart


  /**
     * Draws the overscroll "glow" at the four edges of the chart region, if necessary. The edges
     * of the chart region are stored in {@link #mContentRect}.
     *
     * @see EdgeEffectCompat
     */
    private void drawEdgeEffectsUnclipped(Canvas canvas) {
        // The methods below rotate and translate the canvas as needed before drawing the glow,
        // since EdgeEffectCompat always draws a top-glow at 0,0.

        boolean needsInvalidate = false;

        if (!mEdgeEffectTop.isFinished()) {
            final int restoreCount = canvas.save();
            canvas.translate(mContentRect.left, mContentRect.top);
            mEdgeEffectTop.setSize(mContentRect.width(), mContentRect.height());
            if (mEdgeEffectTop.draw(canvas)) {
                needsInvalidate = true;
            }
            canvas.restoreToCount(restoreCount);
        }

        if (!mEdgeEffectBottom.isFinished()) {
            final int restoreCount = canvas.save();
            canvas.translate(2 * mContentRect.left - mContentRect.right, mContentRect.bottom);
            canvas.rotate(180, mContentRect.width(), 0);
            mEdgeEffectBottom.setSize(mContentRect.width(), mContentRect.height());
            if (mEdgeEffectBottom.draw(canvas)) {
                needsInvalidate = true;
            }
            canvas.restoreToCount(restoreCount);
        }

        if (!mEdgeEffectLeft.isFinished()) {
            final int restoreCount = canvas.save();
            canvas.translate(mContentRect.left, mContentRect.bottom);
            canvas.rotate(-90, 0, 0);
            mEdgeEffectLeft.setSize(mContentRect.height(), mContentRect.width());
            if (mEdgeEffectLeft.draw(canvas)) {
                needsInvalidate = true;
            }
            canvas.restoreToCount(restoreCount);
        }

        if (!mEdgeEffectRight.isFinished()) {
            final int restoreCount = canvas.save();
            canvas.translate(mContentRect.right, mContentRect.top);
            canvas.rotate(90, 0, 0);
            mEdgeEffectRight.setSize(mContentRect.height(), mContentRect.width());
            if (mEdgeEffectRight.draw(canvas)) {
                needsInvalidate = true;
            }
            canvas.restoreToCount(restoreCount);
        }

        if (needsInvalidate) {
            ViewCompat.postInvalidateOnAnimation(this);
        }
    }