android UI 优化之 AbsListView之深度优化

  次阅读 来源:互联网(转载协议) 2015-11-26 09:34 我要评论(0)

android 提供的很多List控件如 listview、gridview 默认都会显示一个fadingedge的东西,它在View的top和bottom处各显示一个渐变半透的阴影以达到更好的视觉效果,但是这个带来的副作 用就是导致在性能不是那么强劲的机器上,一些listview,gridview的拖动会显得很不流畅,因为我们知道绘制带Alpha的图片是最耗时 的。

我们的优化思路就是对这个fadingedge做一些修改,当view处于滚动状态时,通过接口setVerticalFadingEdgeEnabled(false)让其不显示fadingedge,当view处于静止状态时,通过接口setVerticalFadingEdgeEnabled(true)恢复显示fadingedge。以上的listview和gridview等控件都是继承与AbsListView,所以我们直接修改framework中的AbsListView.java文件,就可以达到系统级的改动效果了。

具体修改如下:

@Override

public boolean onTouchEvent(MotionEvent ev) {

if (!isEnabled()) {

// A disabled view that is clickable still consumes the touch

// events, it just doesn't respond to them.

return isClickable() || isLongClickable();

}

if (mFastScroller != null) {

boolean intercepted = mFastScroller.onTouchEvent(ev);

if (intercepted) {

return true;

}

}

final int action = ev.getAction();

View v;

int deltaY;

if (mVelocityTracker == null) {

mVelocityTracker = VelocityTracker.obtain();

}

mVelocityTracker.addMovement(ev);

switch (action & MotionEvent.ACTION_MASK) {

case MotionEvent.ACTION_DOWN: {

setVerticalFadingEdgeEnabled(false);

mActivePointerId = ev.getPointerId(0);

final int x = (int) ev.getX();

final int y = (int) ev.getY();

int motionPosition = pointToPosition(x, y);

if (!mDataChanged) {

if ((mTouchMode != TOUCH_MODE_FLING) && (motionPosition >= 0)

&& (getAdapter().isEnabled(motionPosition))) {

// User clicked on an actual view (and was not stopping a fling). It might be a

// click or a scroll. Assume it is a click until proven otherwise

mTouchMode = TOUCH_MODE_DOWN;

// FIXME Debounce

if (mPendingCheckForTap == null) {

mPendingCheckForTap = new CheckForTap();

}

postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());

} else {

if (ev.getEdgeFlags() != 0 && motionPosition < 0) {

// If we couldn't find a view to click on, but the down event was touching

// the edge, we will bail out and try again. This allows the edge correcting

// code in ViewRoot to try to find a nearby view to select

return false;

}

if (mTouchMode == TOUCH_MODE_FLING) {

// Stopped a fling. It is a scroll.

createScrollingCache();

mTouchMode = TOUCH_MODE_SCROLL;

mMotionCorrection = 0;

motionPosition = findMotionRow(y);

reportScrollStateChange(OnScrollListener.SCROLL_STATE_TOUCH_SCROLL);

}

}

}

if (motionPosition >= 0) {

// Remember where the motion event started

v = getChildAt(motionPosition - mFirstPosition);

mMotionViewOriginalTop = v.getTop();

}

mMotionX = x;

mMotionY = y;

mMotionPosition = motionPosition;

mLastY = Integer.MIN_VALUE;

break;

}

case MotionEvent.ACTION_MOVE: {

final int pointerIndex = ev.findPointerIndex(mActivePointerId);

final int y = (int) ev.getY(pointerIndex);

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