基于 Api level 29
暂时先阅读源码吧，等待后续整理。
/**
* Implement this method to handle touch screen motion events.
* <p>
* If this method is used to detect click actions, it is recommended that
* the actions be performed by implementing and calling
* {@link #performClick()}. This will ensure consistent system behavior,
* including:
* <ul>
* <li>obeying click sound preferences
* <li>dispatching OnClickListener calls
* <li>handling {@link AccessibilityNodeInfo#ACTION_CLICK ACTION_CLICK} when
* accessibility features are enabled
* </ul>
*
* @param event The motion event.
* @return True if the event was handled, false otherwise.
*/
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
// 第一步，根据 viewFlags 判断是否 clickable
final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
// 如果 view disabled
if ((viewFlags & ENABLED_MASK) == DISABLED) {
// 如果是 ACTION_UP 且 flag 不是 pressed
// 设置 pressed state 为 false
// 在 Android 的 touchEvent 中 MotionEvent.ACTION_UP 为 onClick() 的触发条件
if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
// A disabled view that is clickable still consumes the touch
// events, it just doesn't respond to them.
// 被 disabled 的 view 仍然「可以」消费 touch event，只是不进行响应
return clickable;
}
// 如果有 TouchDelegate，由 TouchDelegate 处理 touch event
// 一般用来扩大或缩小点击范围
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
// 如果 当前 view 为 clickable 或者 flag 是悬浮提示
// 返回 true 消费掉 touch event
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
switch (action) {
// 抬起事件
case MotionEvent.ACTION_UP:
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
// 处理悬浮提示
if ((viewFlags & TOOLTIP) == TOOLTIP) {
handleTooltipUp();
}
// 非 clickable，恢复
if (!clickable) {
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break;
}
// 当 pressed state 为 true 或 prepressed 时
// 所谓 prepressed 是指当 view 位于可滚动的容器内时，为了优先处理滚动事件，会把当前的 view state 设置为 prepressed
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
// take focus if we don't have it already and we should in
// touch mode.
boolean focusTaken = false;
// 如果 focuable 且未 focused 则尝试获取焦点
if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
focusTaken = requestFocus();
}
// 设置 pressed state 为 true
if (prepressed) {
// The button is being released before we actually
// showed it as pressed. Make it show the pressed
// state now (before scheduling the click) to ensure
// the user sees it.
setPressed(true, x, y);
}
// 如果没有长按事件
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// This is a tap, so remove the longpress check
removeLongPressCallback();
// Only perform take click actions if we were in the pressed state
if (!focusTaken) {
// Use a Runnable and post this rather than calling
// performClick directly. This lets other visual state
// of the view update before click actions start.
// 向主线程 post 一个 PerformClick，失败则直接 performClickInternal()
// 这样在触发点击事件前可以继续更新 view 展示状态
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {
performClickInternal();
}
}
}
if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}
// 如果是 prepressed
// 延迟 duration 后 unset pressed state
// 否则直接向主线程 post，失败则直接 unset pressed state
if (prepressed) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
removeTapCallback();
}
mIgnoreNextUpEvent = false;
break;
// 按下事件
case MotionEvent.ACTION_DOWN:
if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) {
mPrivateFlags3 |= PFLAG3_FINGER_DOWN;
}
mHasPerformedLongPress = false;
// 如果非 clickable
if (!clickable) {
// 为触发长按事件设置 delay
checkForLongClick(
ViewConfiguration.getLongPressTimeout(),
x,
y,
TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
break;
}
// 如果需要响应弹出上下文菜单（鼠标右键）则 break
if (performButtonActionOnTouchDown(event)) {
break;
}
// Walk up the hierarchy to determine if we're inside a scrolling container.
// 检查当前 view 是否为可滚动容器
boolean isInScrollingContainer = isInScrollingContainer();
// For views inside a scrolling container, delay the pressed feedback for
// a short period in case this is a scroll.
// 如果在滚动容器中，延迟反馈 press 事件，以防阻塞滑动事件
if (isInScrollingContainer) {
mPrivateFlags |= PFLAG_PREPRESSED;
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// Not inside a scrolling container, so show the feedback right away
// 此时 view 不在可滚动容器内，直接处理 pressed
setPressed(true, x, y);
// 为触发长按事件设置 delay
checkForLongClick(
ViewConfiguration.getLongPressTimeout(),
x,
y,
TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
}
break;
// 取消事件
case MotionEvent.ACTION_CANCEL:
// 恢复初始
if (clickable) {
setPressed(false);
}
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
break;
// 移动事件
case MotionEvent.ACTION_MOVE:
// 调整触摸位置，例如 ripple 特效等会需要用到这个方法
if (clickable) {
drawableHotspotChanged(x, y);
}
// 获取当前手势的类型
final int motionClassification = event.getClassification();
// 当前手势类型是否为模糊手势
final boolean ambiguousGesture =
motionClassification == MotionEvent.CLASSIFICATION_AMBIGUOUS_GESTURE;
// mTouchSlop 是判断点击与滑动事件的临界点
int touchSlop = mTouchSlop;
// 模糊手势且后续会触发长按事件
if (ambiguousGesture && hasPendingLongPressCallback()) {
final float ambiguousMultiplier =
ViewConfiguration.getAmbiguousGestureMultiplier();
// 如果移出当前 view，取消长按回调
if (!pointInView(x, y, touchSlop)) {
// The default action here is to cancel long press. But instead, we
// just extend the timeout here, in case the classification
// stays ambiguous.
removeLongPressCallback();
long delay = (long) (ViewConfiguration.getLongPressTimeout()
* ambiguousMultiplier);
// Subtract the time already spent
delay -= event.getEventTime() - event.getDownTime();
// 重新为触发长按事件设置 delay
checkForLongClick(
delay,
x,
y,
TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
}
touchSlop *= ambiguousMultiplier;
}
// Be lenient about moving outside of buttons
// 如果移出当前 view，取消长按、单击回调；设置 pressed state 为 false
if (!pointInView(x, y, touchSlop)) {
// Outside button
// Remove any future long press/tap checks
removeTapCallback();
removeLongPressCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
}
// 如果是 deepPress（也就是屏幕力度感应）则触发长按事件的 delay 为 0，即立即触发
final boolean deepPress =
motionClassification == MotionEvent.CLASSIFICATION_DEEP_PRESS;
if (deepPress && hasPendingLongPressCallback()) {
// process the long click action immediately
removeLongPressCallback();
checkForLongClick(
0 /* send immediately */,
x,
y,
TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__DEEP_PRESS);
}
break;
}
return true;
}
// 非 clickable，不消费 touch event，事件将向上层（parent）传递
return false;
}// 当 view long_clickable 为 true 或 flag 为悬浮提示时
// 为长按事件设置一个 delay，当 delay 到达时向主线程 post 长按事件
private void checkForLongClick(long delay, float x, float y, int classification) {
if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE || (mViewFlags & TOOLTIP) == TOOLTIP) {
mHasPerformedLongPress = false;
if (mPendingCheckForLongPress == null) {
mPendingCheckForLongPress = new CheckForLongPress();
}
mPendingCheckForLongPress.setAnchor(x, y);
mPendingCheckForLongPress.rememberWindowAttachCount();
mPendingCheckForLongPress.rememberPressedState();
mPendingCheckForLongPress.setClassification(classification);
postDelayed(mPendingCheckForLongPress, delay);
}
} /**
* Performs button-related actions during a touch down event.
*
* @param event The event.
* @return True if the down was consumed.
*
* @hide
*/
protected boolean performButtonActionOnTouchDown(MotionEvent event) {
// 事件来源为鼠标且单击右键时，展示上下文菜单
if (event.isFromSource(InputDevice.SOURCE_MOUSE) &&
(event.getButtonState() & MotionEvent.BUTTON_SECONDARY) != 0) {
showContextMenu(event.getX(), event.getY());
mPrivateFlags |= PFLAG_CANCEL_NEXT_UP_EVENT;
return true;
}
return false;
} /**
* Call this view's OnClickListener, if it is defined. Performs all normal
* actions associated with clicking: reporting accessibility event, playing
* a sound, etc.
*
* @return True there was an assigned OnClickListener that was called, false
* otherwise is returned.
*/
// NOTE: other methods on View should not call this method directly, but performClickInternal()
// instead, to guarantee that the autofill manager is notified when necessary (as subclasses
// could extend this method without calling super.performClick()).
public boolean performClick() {
// We still need to call this method to handle the cases where performClick() was called
// externally, instead of through performClickInternal()
// 在 performClickInternal() 方法中已经调用过该方法，这里再次调用是作为从其他路径进入的兜底
notifyAutofillManagerOnClick();
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
// 点击音效
playSoundEffect(SoundEffectConstants.CLICK);
// 点击事件的回调
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
notifyEnterOrExitForAutoFillIfNeeded(true);
return result;
} /**
* Utility method to determine whether the given point, in local coordinates,
* is inside the view, where the area of the view is expanded by the slop factor.
* This method is called while processing touch-move events to determine if the event
* is still within the view.
*
* @hide
*/
@UnsupportedAppUsage
public boolean pointInView(float localX, float localY, float slop) {
return localX >= -slop && localY >= -slop && localX < ((mRight - mLeft) + slop) && localY < ((mBottom - mTop) + slop);
}