編輯：關於Android編程
事件機制是Android中一個比較復雜且重要的知識點，比如你想自定義攔截事件，或者某系組件中嵌套了其他布局，往往會出現這樣那樣的事件沖突，坑爹啊！！事件主要涵蓋onTouch，onClick，onTouchEvent，dispatchTouchEvent，onInterceptTouchEvent等等一系列事件，並且事件間還相互交互耦合，甚至有的事件還有返回值，一會true，一會false，什麼情況下返回true，什麼情況下返回false，為什麼要有返回值，想想這些就感覺整個人都不好了。
但是（萬惡的但是），該知識點還是必須要掌握的，知識的深度與廣度決定了你走的遠度，鑒於此我們就來捅一捅該知識點。
俗話說工欲善其事必先利其器，為了看他的執行流程，我們還是先寫個樣例，打幾個日志看看執行流程吧！
首先自定義一個外層布局的Layout，自定義Layout繼承了LinearLayout，復寫了相應的函數，在調用之前輸入日志。如下：
public class Layout extends LinearLayout {
public Layout(Context context) {
super(context);
init();
}
public Layout(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public Layout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
private void init() {
//requestDisallowInterceptTouchEvent(false);
}
@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
Log.e("Event", "Layout onInterceptTouchEvent " + MotionEvent.actionToString(ev.getAction()));
return super.onInterceptTouchEvent(ev);
}
@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.e("Event", "Layout onTouchEvent " + MotionEvent.actionToString(event.getAction()));
return super.onTouchEvent(event);
}
@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.e("Event", "Layout dispatchTouchEvent " + MotionEvent.actionToString(event.getAction()));
return super.dispatchTouchEvent(event);
}
}
我們還自定義了一個LogTextView，繼承自TextView，也是為了輸出日志，代碼如下：
public class LogTextView extends TextView {
public LogTextView(Context context) {
super(context);
}
public LogTextView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public LogTextView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.e("Event", "TextView onTouchEvent " + MotionEvent.actionToString(event.getAction()));
return super.onTouchEvent(event);
}
@Override
public void setOnTouchListener(OnTouchListener l) {
super.setOnTouchListener(l);
}
@Override
public void setOnClickListener(OnClickListener l) {
super.setOnClickListener(l);
}
}
接下來是布局文件了：
布局中嵌套了兩個view，一個TextView，一個ImageView。最後就是主界面了。
public class MainActivity extends AppCompatActivity {
private LogTextView tv;
private ImageView imageView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViews();
setViewListener();
}
private void findViews() {
tv = (LogTextView) findViewById(R.id.textView);
imageView = (ImageView) findViewById(R.id.image);
}
private void setViewListener() {
tv.setOnTouchListener(new View.OnTouchListener() {
@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.e("Event", "TextView onTouch " + MotionEvent.actionToString(event.getAction()));
return true;
}
});
tv.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.e("Event", "TextView onClick ");
}
});
imageView.setOnTouchListener(new View.OnTouchListener() {
@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.e("Event", "ImageView onTouch " + MotionEvent.actionToString(event.getAction()));
return false;
}
});
imageView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.e("Event", "ImageView onClick ");
}
});
}
}
round 1
TextView的onTouch返回為false，點擊TextView，日志如下：
05-05 14:04:44.091 27644-27644/com.sunny.event E/Event: Layout dispatchTouchEvent ACTION_DOWN
05-05 14:04:44.091 27644-27644/com.sunny.event E/Event: Layout onInterceptTouchEvent ACTION_DOWN
05-05 14:04:44.091 27644-27644/com.sunny.event E/Event: TextView onTouch ACTION_DOWN
05-05 14:04:44.091 27644-27644/com.sunny.event E/Event: TextView onTouchEvent ACTION_DOWN
05-05 14:04:44.158 27644-27644/com.sunny.event E/Event: Layout dispatchTouchEvent ACTION_MOVE
05-05 14:04:44.158 27644-27644/com.sunny.event E/Event: Layout onInterceptTouchEvent ACTION_MOVE
05-05 14:04:44.158 27644-27644/com.sunny.event E/Event: TextView onTouch ACTION_MOVE
05-05 14:04:44.158 27644-27644/com.sunny.event E/Event: TextView onTouchEvent ACTION_MOVE
05-05 14:04:44.158 27644-27644/com.sunny.event E/Event: Layout dispatchTouchEvent ACTION_UP
05-05 14:04:44.159 27644-27644/com.sunny.event E/Event: Layout onInterceptTouchEvent ACTION_UP
05-05 14:04:44.159 27644-27644/com.sunny.event E/Event: TextView onTouch ACTION_UP
05-05 14:04:44.159 27644-27644/com.sunny.event E/Event: TextView onTouchEvent ACTION_UP
05-05 14:04:44.159 27644-27644/com.sunny.event E/Event: TextView onClick
根據日志我們可以看到首先有一個ACTION_DOWN事件，執行的順序是Layout的dispatchTouchEvent→onInterceptTouchEvent→（TextView）onTouch要→onTouchEvent，之後的我帕金森發生了，產生了ACTION_MOVE事件，傳遞的順序與Down是一致的，最後一個事件是UP事件，正常點擊不滑動是不會產生MOVE事件的，在這個這個三個事件最後調用了TextView的onClick事件。
小結：
1 . 事件的傳遞順序是先外層容器，之後再是具體的View。
2. onTouch事件先於onTouchEvent事件，onTouchEvent先於onClick事件
round 2
我們將TextView的onTouch事件返回true。重新執行。執行順序如下：
05-05 14:10:20.556 27644-27644/com.sunny.event E/Event: Layout dispatchTouchEvent ACTION_DOWN
05-05 14:10:20.556 27644-27644/com.sunny.event E/Event: Layout onInterceptTouchEvent ACTION_DOWN
05-05 14:10:20.556 27644-27644/com.sunny.event E/Event: TextView onTouch ACTION_DOWN
05-05 14:10:20.616 27644-27644/com.sunny.event E/Event: Layout dispatchTouchEvent ACTION_MOVE
05-05 14:10:20.616 27644-27644/com.sunny.event E/Event: Layout onInterceptTouchEvent ACTION_MOVE
05-05 14:10:20.616 27644-27644/com.sunny.event E/Event: TextView onTouch ACTION_MOVE
05-05 14:10:20.622 27644-27644/com.sunny.event E/Event: Layout dispatchTouchEvent ACTION_UP
05-05 14:10:20.622 27644-27644/com.sunny.event E/Event: Layout onInterceptTouchEvent ACTION_UP
05-05 14:10:20.622 27644-27644/com.sunny.event E/Event: TextView onTouch ACTION_UP
從日志可以看出如果onTouch返回為true，執行順序變成了如下：
首先還是ACTION_DOWN事件（Layout）dispatchTouchEvent→onInterceptTouchEvent→（TextView）onTouch，ACTION_MOVE與ACTION_UP執行順序同ACTION_DOWN，可以發現的是TextView的onTouchEvent事件沒有了，並且onClick事件也沒有了。
小結
1，onTouch事件的返回值為true會攔截onTouchEvent事件
2，onTouchEvent與onClick有關聯
上面的兩次執行中每次都調用了onInterceptTouchEvent事件，這個到底又是啥？我們去看看他的返回值是什麼？
public boolean onInterceptTouchEvent(MotionEvent ev) {
return false;
}
可以看到默認返回false，注釋長的嚇人，那我們就來改寫一下他的返回值，這個函數是ViewGroup才有的，說明與布局容器有關.
round 3
我們將Layout的onInterceptTouchEvent的返回值改為true。重新執行。執行順序如下：
05-05 14:59:17.829 15157-15157/com.sunny.event E/Event: Layout dispatchTouchEvent ACTION_DOWN
05-05 14:59:17.830 15157-15157/com.sunny.event E/Event: Layout onInterceptTouchEvent ACTION_DOWN
05-05 14:59:17.830 15157-15157/com.sunny.event E/Event: Layout onTouchEvent ACTION_DOWN
從日志可以發現，只有最外層的控件能夠執行事件，TextView已經收不到任何事件。
小結
父控件onInterceptTouchEvent返回true會攔截子控件的事件
我們從代碼的層面來看看他是怎麼執行的，當屏幕接收到點擊事件時會首先傳遞到Activity的dispatchTouchEvent：
/**
* Called to process touch screen events. You can override this to
* intercept all touch screen events before they are dispatched to the
* window. Be sure to call this implementation for touch screen events
* that should be handled normally.
*
* @param ev The touch screen event.
*
* @return boolean Return true if this event was consumed.
*/
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
在這裡執行了三步，
1.第一告訴用戶ACTION_DOWN，用戶可以復寫onUserInteraction來處理點擊開始
2.調用了getWindow().superDispatchTouchEvent(ev)，這裡的getWindow得到是PhoneWindow對象，因此執行的PhoneWindow的superDispatchTouchEvent函數，
3.調用了Activity的onTouchEvent事件
PhoneWindow的superDispatchTouchEvent又調用了DecorView的superDispatchTouchEvent函數，每一個Activity都有一個PhoneWindow，每一個PhoneWindow都有一個DecorView，DecoView繼承自FrameLayout，這裡又調用了super.dispatchTouchEvent(event)，FrameLayout裡面是沒有改函數的，所以最終執行的是ViewGroup的dispatchTouchEvent函數。
這裡我們先穿插一點界面的知識，以我測試手機為例，DecorView中有兩個child，分別是ViewStub和LinerLayout，LinerLayout中又包含了FrameLayout，FrameLayout中包含了一個ActionBarOverlayLayout，ActionBarOverlayLayout裡又包含了兩個child，分別是ActionBarContainer與ContentFrameLayout。
接下來我們去看看ViewGroup的dispatchTouchEvent函數：
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
.........
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) {
cancelAndClearTouchTargets(ev);
resetTouchState();
}
// Check for interception.
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false;
}
} else {
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
intercepted = true;
}
............
// Update list of touch targets for pointer down, if needed.
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) {
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
final int actionIndex = ev.getActionIndex(); // always 0 for down
final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
: TouchTarget.ALL_POINTER_IDS;
// Clean up earlier touch targets for this pointer id in case they
// have become out of sync.
removePointersFromTouchTargets(idBitsToAssign);
final int childrenCount = mChildrenCount;
if (newTouchTarget == null && childrenCount != 0) {
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
// Find a child that can receive the event.
// Scan children from front to back.
final ArrayList preorderedList = buildOrderedChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = customOrder
? getChildDrawingOrder(childrenCount, i) : i;
final View child = (preorderedList == null)
? children[childIndex] : preorderedList.get(childIndex);
.......
if (!canViewReceivePointerEvents(child) || !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
// Child is already receiving touch within its bounds.
// Give it the new pointer in addition to the ones it is handling.
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUpFlag(child);
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
if (preorderedList != null) {
// childIndex points into presorted list, find original index
for (int j = 0; j < childrenCount; j++) {
if (children[childIndex] == mChildren[j]) {
mLastTouchDownIndex = j;
break;
}
}
} else {
mLastTouchDownIndex = childIndex;
}
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
}
if (preorderedList != null) preorderedList.clear();
}
if (newTouchTarget == null && mFirstTouchTarget != null) {
// Did not find a child to receive the event.
// Assign the pointer to the least recently added target.
newTouchTarget = mFirstTouchTarget;
while (newTouchTarget.next != null) {
newTouchTarget = newTouchTarget.next;
}
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
}
}
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
// Dispatch to touch targets, excluding the new touch target if we already
// dispatched to it. Cancel touch targets if necessary.
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
if (dispatchTransformedTouchEvent(ev, cancelChild, target.child, target.pointerIdBits)) {
handled = true;
}
if (cancelChild) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
}
// Update list of touch targets for pointer up or cancel, if needed.
if (canceled || actionMasked == MotionEvent.ACTION_UP
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
resetTouchState();
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
}
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}
我們只看最重要的部分
1： 事件為ACTION_DOWN時，執行了cancelAndClearTouchTargets函數，該函數主要清除上一次點擊傳遞的路徑，之後執行了resetTouchState，重置了touch狀態，其中執行了 mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;就是攔截狀態為false，這個與requestDisallowInterceptTouchEvent函數相關。
2： 獲取intercepted的值，首先判斷了disallowIntercept狀態，是否攔截子控件的事件執行。從代碼可以看到當disallowIntercept為false時，該狀態主要取決於onInterceptTouchEvent函數的返回值，這就是前面我們攔截的函數，如果為true，這時intercepted為true標識攔截。
3： 接著判斷了!canceled && !intercepted的值，canceled這裡為false，如果intercepted為false，則會進入判斷條件，這裡假設不攔截，進入後繼續判斷如果是ACTION_DOWN事件，則會繼續進入判斷，遍歷所有子控件，isTransformedTouchPointInView會判斷當前點擊區域是否在控件內，如果不在則遍歷下一個，之後調用dispatchTransformedTouchEvent函數。最後在調用addTouchTarget函數，將當前選中的控件，掛載到當前點擊目標鏈表。alreadyDispatchedToNewTouchTarget賦值為true。
接著判斷mFirstTouchTarget是否為空，經過上一步的addTouchTarget的執行，這裡mFirstTouchTarget不為空。第一個事件alreadyDispatchedToNewTouchTarget為true，且target == newTouchTarget，因此handled值為true，如果是後續的事件，則會進入dispatchTransformedTouchEvent中。
我們接著看看第三部中的dispatchTransformedTouchEvent函數：
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
// Calculate the number of pointers to deliver.
final int oldPointerIdBits = event.getPointerIdBits();
final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits;
.......
final MotionEvent transformedEvent;
if (newPointerIdBits == oldPointerIdBits) {
if (child == null || child.hasIdentityMatrix()) {
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
final float offsetX = mScrollX - child.mLeft;
final float offsetY = mScrollY - child.mTop;
event.offsetLocation(offsetX, offsetY);
handled = child.dispatchTouchEvent(event);
event.offsetLocation(-offsetX, -offsetY);
}
return handled;
}
transformedEvent = MotionEvent.obtain(event);
} else {
transformedEvent = event.split(newPointerIdBits);
}
.......
// Done.
transformedEvent.recycle();
return handled;
}
這裡會進入到第10行，且傳遞過來的child不為空，因此會繼續執行child.dispatchTouchEvent，這裡繼續執行ViewGroup的dispatchTouchEvent，一直遞歸執行，直到真正接受點擊的控件，到最後child會為空，這裡要麼是一個View控件，要麼是未包含任何子控件的ViewGroup，這時這裡會執行View的dispatchTouchEvent。
從上述執行邏輯可以直到，先從DecorView一直遞歸到Layout，最後再到TextView，這裡我們去看看View的dispatchTouchEvent：
public boolean dispatchTouchEvent(MotionEvent event) {
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Defensive cleanup for new gesture
stopNestedScroll();
}
if (onFilterTouchEventForSecurity(event)) {
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
if (!result && onTouchEvent(event)) {
result = true;
}
}
if (!result && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
// Clean up after nested scrolls if this is the end of a gesture;
// also cancel it if we tried an ACTION_DOWN but we didn't want the rest
// of the gesture.
if (actionMasked == MotionEvent.ACTION_UP || actionMasked == MotionEvent.ACTION_CANCEL ||
(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
stopNestedScroll();
}
return result;
}
首先會停止掉嵌套滑動，之後先判斷了ListenerInfo不為空，這裡只要是設置了onTouch，onKey，onHover，onDrag等等中的任何一個這裡就不為空，具體可以去看看ListenerInfo包含的listenerInfo類型。其次判斷了mOnTouchListener不為空，只要設置了onTouchListener這裡就不為空，再之後判斷了該控件是否是enabled，一般都會enabled，可以代碼設置為false，再之後調用了mOnTouchListener的onTouch事件，這裡就是外面傳進來的onTouchListener，從這裡可以看到無論onTouch返回任何值，onTouch事件都會執行，但是如果返回為true，則會導致result為true，!result && onTouchEvent(event)因為短路，不會執行到onTouchEvent事件。
小結
1：onTouch返回為true導致onTouchEvent不能執行
2：如果enable為false，因為短路onTouch不會執行
到此還沒有看到任何onClick事件的執行，我們繼續去看看onTouchEvent函數：
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction()；
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
(viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
switch (action) {
case MotionEvent.ACTION_UP:
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;
if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
focusTaken = requestFocus();
}
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);
}
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.
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {
performClick();
}
}
}
if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}
if (prepressed) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
removeTapCallback();
}
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_DOWN:
mHasPerformedLongPress = false;
if (performButtonActionOnTouchDown(event)) {
break;
}
// Walk up the hierarchy to determine if we're inside a scrolling container.
boolean isInScrollingContainer = isInScrollingContainer();
// For views inside a scrolling container, delay the pressed feedback for
// a short period in case this is a scroll.
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
setPressed(true, x, y);
checkForLongClick(0);
}
break;
case MotionEvent.ACTION_CANCEL:
setPressed(false);
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_MOVE:
drawableHotspotChanged(x, y);
// Be lenient about moving outside of buttons
if (!pointInView(x, y, mTouchSlop)) {
// Outside button
removeTapCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
// Remove any future long press/tap checks
removeLongPressCallback();
setPressed(false);
}
}
break;
}
return true;
}
return false;
}
我們首先看ACTION_DOWN事件，這裡主要看checkForLongClick，CheckForTap中也調用了該函數，這裡就是添加一個長按事件，如果達到長按標准且長按listener不為空，則執行長按事件，接著我們看ACTION_UP，這裡看到如果不是長按事件，則調用了performClick，performClick裡面執行了onClick事件。
小結
1：onClick事件與onLongClick事件是在onTouchEvent中執行的
2：如果執行了長按事件則onClick不執行
3：就api 23代碼，長按的時間間隔為500毫秒
上面解析了intercepted為false的情況，那intercepted為true，它到底是怎麼攔截的？
如果intercepted為true，則!canceled && !intercepted為false，不能進入該判斷，mFirstTouchTarget為空，會繼續執行如下分支：
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
}
這裡第三參數傳遞的child為null，因此就會執行該控件onTouch與onTouchEvent函數，不會繼續遞歸傳遞，因此也就攔截了子控件的執行。
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