TouchEvent分发过程二：ListView中TouchEvent的处理
在TouchEvent分发过程一：TouchEvent在ViewGroup中的分发过程中，分析了TouchEvent在ViewGroup中的分发过程。为了了解复杂容器中如何处理TouchEvent的分发，本文将简单分析一下TouchEvent在ListView中的分发过程。
ListView继承自AbsListView，AbsListView继承自ViewGroup并重写了onInterceptTouchEvent和onTouchEvent方法。
首先分析onInterceptTouchEvent的处理：
switch (action & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN: {
int touchMode = mTouchMode;
if (touchMode == TOUCH_MODE_OVERFLING || touchMode == TOUCH_MODE_OVERSCROLL) {
mMotionCorrection = 0;
return true;
}
final int x = (int) ev.getX();
final int y = (int) ev.getY();
mActivePointerId = ev.getPointerId(0);
int motionPosition = findMotionRow(y);
if (touchMode != TOUCH_MODE_FLING && motionPosition >= 0) {
// User clicked on an actual view (and was not stopping a fling).
// Remember where the motion event started
v = getChildAt(motionPosition - mFirstPosition);
mMotionViewOriginalTop = v.getTop();
mMotionX = x;
mMotionY = y;
mMotionPosition = motionPosition;
mTouchMode = TOUCH_MODE_DOWN;
clearScrollingCache();
}
mLastY = Integer.MIN_VALUE;
initOrResetVelocityTracker();
mVelocityTracker.addMovement(ev);
if (touchMode == TOUCH_MODE_FLING) {
return true;
}
break;
}
}
在ListView处于滚动状态或滚动到超出范围时，回返回true，从而截断TouchEvent。
但是滚动过程中的ACTION_DOWN会被记录下来。
case MotionEvent.ACTION_MOVE: {
switch (mTouchMode) {
case TOUCH_MODE_DOWN:
int pointerIndex = ev.findPointerIndex(mActivePointerId);
if (pointerIndex == -1) {
pointerIndex = 0;
mActivePointerId = ev.getPointerId(pointerIndex);
}
final int y = (int) ev.getY(pointerIndex);
initVelocityTrackerIfNotExists();
mVelocityTracker.addMovement(ev);
if (startScrollIfNeeded(y)) {
return true;
}
break;
}
break;
}
startScrollIfNeeded(y)用于判断在ACTION_MOVE事件发生时，是否已经移动了足够的距离使该TouchEvent能够被当做滚动事件处理，如果是，mTouchMode被修改为TOUCH_MODE_SCROLL，同时设置其父控件不能截断TouchEvent，此时onInterceptTouchEvent返回true，这样当ACTION_UP发生时就不会被传递到ListView的子控件，从而不会发生ItemClick事件；如果不是返回false。因此ListView滚动时，其父控件和子控件都不能处理TouchEvent。
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP: {
mTouchMode = TOUCH_MODE_REST;
mActivePointerId = INVALID_POINTER;
recycleVelocityTracker();
reportScrollStateChange(OnScrollListener.SCROLL_STATE_IDLE);
break;
}
该部分主要用于重置状态及滚动相关助手类。
再看onTouchEvent的处理：
case MotionEvent.ACTION_DOWN: {
switch (mTouchMode) {
case TOUCH_MODE_OVERFLING: {
mFlingRunnable.endFling();
if (mPositionScroller != null) {
mPositionScroller.stop();
}
mTouchMode = TOUCH_MODE_OVERSCROLL;
mMotionX = (int) ev.getX();
mMotionY = mLastY = (int) ev.getY();
mMotionCorrection = 0;
mActivePointerId = ev.getPointerId(0);
mDirection = 0;
break;
}
default: {
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 (mTouchMode == TOUCH_MODE_FLING) {
// Stopped a fling. It is a scroll.
createScrollingCache();
mTouchMode = TOUCH_MODE_SCROLL;
mMotionCorrection = 0;
motionPosition = findMotionRow(y);
mFlingRunnable.flywheelTouch();
}
}
}
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;
}
}
if (performButtonActionOnTouchDown(ev)) {
if (mTouchMode == TOUCH_MODE_DOWN) {
removeCallbacks(mPendingCheckForTap);
}
}
break;
}
ACTION_DOWN的处理主要是记录发生时的坐标。
case MotionEvent.ACTION_MOVE: {
int pointerIndex = ev.findPointerIndex(mActivePointerId);
if (pointerIndex == -1) {
pointerIndex = 0;
mActivePointerId = ev.getPointerId(pointerIndex);
}
final int y = (int) ev.getY(pointerIndex);
switch (mTouchMode) {
case TOUCH_MODE_DOWN:
case TOUCH_MODE_TAP:
case TOUCH_MODE_DONE_WAITING:
// Check if we have moved far enough that it looks more like a
// scroll than a tap
startScrollIfNeeded(y);
break;
case TOUCH_MODE_SCROLL:
case TOUCH_MODE_OVERSCROLL:
scrollIfNeeded(y);
break;
}
break;
}
ACTION_MOVE主要实现滚动逻辑。
case MotionEvent.ACTION_UP: {
switch (mTouchMode) {
case TOUCH_MODE_DOWN:
case TOUCH_MODE_TAP:
case TOUCH_MODE_DONE_WAITING:
final int motionPosition = mMotionPosition;
final View child = getChildAt(motionPosition - mFirstPosition);
final float x = ev.getX();
final boolean inList = x > mListPadding.left && x < getWidth() - mListPadding.right;
if (child != null && !child.hasFocusable() && inList) {
if (mTouchMode != TOUCH_MODE_DOWN) {
child.setPressed(false);
}
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
final AbsListView.PerformClick performClick = mPerformClick;
performClick.mClickMotionPosition = motionPosition;
performClick.rememberWindowAttachCount();
mResurrectToPosition = motionPosition;
if (mTouchMode == TOUCH_MODE_DOWN || mTouchMode == TOUCH_MODE_TAP) {
final Handler handler = getHandler();
if (handler != null) {
handler.removeCallbacks(mTouchMode == TOUCH_MODE_DOWN ?
mPendingCheckForTap : mPendingCheckForLongPress);
}
mLayoutMode = LAYOUT_NORMAL;
if (!mDataChanged && mAdapter.isEnabled(motionPosition)) {
mTouchMode = TOUCH_MODE_TAP;
setSelectedPositionInt(mMotionPosition);
layoutChildren();
child.setPressed(true);
positionSelector(mMotionPosition, child);
setPressed(true);
if (mSelector != null) {
Drawable d = mSelector.getCurrent();
if (d != null && d instanceof TransitionDrawable) {
((TransitionDrawable) d).resetTransition();
}
}
if (mTouchModeReset != null) {
removeCallbacks(mTouchModeReset);
}
mTouchModeReset = new Runnable() {
@Override
public void run() {
mTouchMode = TOUCH_MODE_REST;
child.setPressed(false);
setPressed(false);
if (!mDataChanged) {
performClick.run();
}
}
};
postDelayed(mTouchModeReset,
ViewConfiguration.getPressedStateDuration());
} else {
mTouchMode = TOUCH_MODE_REST;
updateSelectorState();
}
return true;
} else if (!mDataChanged && mAdapter.isEnabled(motionPosition)) {
performClick.run();
}
}
mTouchMode = TOUCH_MODE_REST;
updateSelectorState();
break;
case TOUCH_MODE_SCROLL:
final int childCount = getChildCount();
if (childCount > 0) {
final int firstChildTop = getChildAt(0).getTop();
final int lastChildBottom = getChildAt(childCount - 1).getBottom();
final int contentTop = mListPadding.top;
final int contentBottom = getHeight() - mListPadding.bottom;
if (mFirstPosition == 0 && firstChildTop >= contentTop &&
mFirstPosition + childCount < mItemCount &&
lastChildBottom <= getHeight() - contentBottom) {
mTouchMode = TOUCH_MODE_REST;
reportScrollStateChange(OnScrollListener.SCROLL_STATE_IDLE);
} else {
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
final int initialVelocity = (int)
(velocityTracker.getYVelocity(mActivePointerId) * mVelocityScale);
// Fling if we have enough velocity and we aren't at a boundary.
// Since we can potentially overfling more than we can overscroll, don't
// allow the weird behavior where you can scroll to a boundary then
// fling further.
if (Math.abs(initialVelocity) > mMinimumVelocity &&
!((mFirstPosition == 0 &&
firstChildTop == contentTop - mOverscrollDistance) ||
(mFirstPosition + childCount == mItemCount &&
lastChildBottom == contentBottom + mOverscrollDistance))) {
if (mFlingRunnable == null) {
mFlingRunnable = new FlingRunnable();
}
reportScrollStateChange(OnScrollListener.SCROLL_STATE_FLING);
mFlingRunnable.start(-initialVelocity);
} else {
mTouchMode = TOUCH_MODE_REST;
reportScrollStateChange(OnScrollListener.SCROLL_STATE_IDLE);
if (mFlingRunnable != null) {
mFlingRunnable.endFling();
}
if (mPositionScroller != null) {
mPositionScroller.stop();
}
}
}
} else {
mTouchMode = TOUCH_MODE_REST;
reportScrollStateChange(OnScrollListener.SCROLL_STATE_IDLE);
}
break;
case TOUCH_MODE_OVERSCROLL:
if (mFlingRunnable == null) {
mFlingRunnable = new FlingRunnable();
}
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
final int initialVelocity = (int) velocityTracker.getYVelocity(mActivePointerId);
reportScrollStateChange(OnScrollListener.SCROLL_STATE_FLING);
if (Math.abs(initialVelocity) > mMinimumVelocity) {
mFlingRunnable.startOverfling(-initialVelocity);
} else {
mFlingRunnable.startSpringback();
}
break;
}
setPressed(false);
if (mEdgeGlowTop != null) {
mEdgeGlowTop.onRelease();
mEdgeGlowBottom.onRelease();
}
// Need to redraw since we probably aren't drawing the selector anymore
invalidate();
final Handler handler = getHandler();
if (handler != null) {
handler.removeCallbacks(mPendingCheckForLongPress);
}
recycleVelocityTracker();
mActivePointerId = INVALID_POINTER;
if (PROFILE_SCROLLING) {
if (mScrollProfilingStarted) {
Debug.stopMethodTracing();
mScrollProfilingStarted = false;
}
}
if (mScrollStrictSpan != null) {
mScrollStrictSpan.finish();
mScrollStrictSpan = null;
}
break;
}
ACTION_UP事件发生时，
如果没有被判定为是滚动事件，则引起一个click事件。
如果被判定为滚动事件，则需要根据速度判断是否是一个FLING事件，如果是则需要继续滚动，如果不是则立即停止滚动。