The Activity->ViewGroup event is sent from the Activity->ViewGroup event. The Activity->ViewGroup event is sent from the ViewGroup event.
[Android Event Distribution decryption – ViewGroup distribution] (Blog.csdn.net/qq_32865887…)
This article mainly introduces the View for the event processing, obviously in the dispatchTouchEvent() method, directly on the code (this article analysis source code based on Android 10, there are some variations in each version of the source, but the basic principle is the same) :
1.1 View.dispatchTouchEvent()
/** * source code analysis: view.dispatchTouchEvent () */
public boolean dispatchTouchEvent(MotionEvent event) {
/ /... Post only important code
boolean result = false;
/ /...
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Stop sliding if there are nested slides
stopNestedScroll();
}
// Check the security of events
if (onFilterTouchEventForSecurity(event)) {
// Check whether the View is enabled. Check whether the View processes scroll bar events
Rerult =true if you are handling scrollbar events
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
// Key analysis 1:
GetListenerInfo () is assigned a value. There are a number of places that getListenerInfo() calls, and it can be assumed that the Listener interface is not empty
In the setOnTouchListener(OnTouchListener l) method, it is not null as long as the subclass implements this method
// Check whether View is enabled
// Check whether the onTouch method of mOnTouchListener returns true
// Conclusion: If the subclass calls the setOnTouchListener method and implements the mOnTouchListener interface onTouch() method returns true result=true
ListenerInfo li = mListenerInfo;
if(li ! =null&& li.mOnTouchListener ! =null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
If result=true, onTouchEvent() will not go
if(! result && onTouchEvent(event)) { result =true; }}/ /...
return result;
}
Copy the code1.2 View.onTouchEvent()
View.ontouchevent () */
public boolean onTouchEvent(MotionEvent event) {
/ /... Post only important code
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
// Check whether the View can be clicked (click, long click, content click)
final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
// A disabled View also consumes click events, but does not respond
if ((viewFlags & ENABLED_MASK) == DISABLED) {
if(action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) ! =0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
return clickable;
}
/ /...
// Judgment value 1: the control can be clicked to enter the switch judgment value 2: the control is suspended or can be long pressed
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
switch (action) {
// a. If the current event = raise view (main analysis)
case MotionEvent.ACTION_UP:
/ /... After a series of judgments, omitted here
/ / create PerformClick
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
// Execute performClick() performClickInternal calls performClick() ->> Analyze 1
performClickInternal();
/ /...
mIgnoreNextUpEvent = false;
break;
// b. If current event = Press View
case MotionEvent.ACTION_DOWN:
/ /... You know, a bunch of judgments
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
// Execute the postDelayed method
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
/ /...
}
break;
// c. If the current event = end event (no human cause
case MotionEvent.ACTION_CANCEL:
if (clickable) {
setPressed(false);
}
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
break;)// d. If current event = slide view
case MotionEvent.ACTION_MOVE:
/ /...
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;
}
/ /...
break;
}
return true;
}
return false;
}
PerformClick () */
public boolean performClick(a) {
notifyAutofillManagerOnClick();
final boolean result;
final ListenerInfo li = mListenerInfo;
if(li ! =null&& li.mOnClickListener ! =null) {
// You can use this method to set click sounds
playSoundEffect(SoundEffectConstants.CLICK);
// If we register a click event for the control View with the setOnClickListener () method
// Then the mOnClickListener variable will be assigned a value (i.e., not null)
// Then onClick () is called back and performClick () returns true
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}
/ /...
return result;
}
Copy the code1.3 Summary of View Event Handling
When the user clicks on the control:
1.4 case Demo
public class MainActivity extends AppCompatActivity {
private Button btn_click;
private static final String TAG = "MainActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn_click = findViewById(R.id.btn_click);
btn_click.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.e(TAG, "onClick"); }}); btn_click.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.e(TAG, "onTouch: " + event.getAction());
return true; }}); }}Copy the codeThe log is as follows: 1. OnTouch returns true
2021-03-18 14:54:12.109 18268-18268/com.enjoy.clickevent E/MainActivity: onTouch: 0
2021-03-18 14:54:12.132 18268-18268/com.enjoy.clickevent E/MainActivity: onTouch: 2
2021-03-18 14:54:12.182 18268-18268/com.enjoy.clickevent E/MainActivity: onTouch: 2
2021-03-18 14:54:12.194 18268-18268/com.enjoy.clickevent E/MainActivity: onTouch: 2
2021-03-18 14:54:12.195 18268-18268/com.enjoy.clickevent E/MainActivity: onTouch: 1
Copy the code2. The onTouch returns false
2021-03-18 14:59:13.795 19243-19243/com.enjoy.clickevent E/MainActivity: onTouch: 0
2021-03-18 14:59:13.808 19243-19243/com.enjoy.clickevent E/MainActivity: onTouch: 2
2021-03-18 14:59:13.824 19243-19243/com.enjoy.clickevent E/MainActivity: onTouch: 2
2021-03-18 14:59:13.841 19243-19243/com.enjoy.clickevent E/MainActivity: onTouch: 2
2021-03-18 14:59:13.857 19243-19243/com.enjoy.clickevent E/MainActivity: onTouch: 2
2021-03-18 14:59:13.891 19243-19243/com.enjoy.clickevent E/MainActivity: onTouch: 2
2021-03-18 14:59:13.895 19243-19243/com.enjoy.clickevent E/MainActivity: onTouch: 2
2021-03-18 14:59:13.896 19243-19243/com.enjoy.clickevent E/MainActivity: onTouch: 1
2021-03-18 14:59:13.898 19243-19243/com.enjoy.clickevent E/MainActivity: onClick
Copy the codeI believe that you should have a general understanding of Android event distribution and processing, and finally summarize:
-
Android event distribution is passed first to the ViewGroup and then from the ViewGroup to the View.
-
In ViewGroup, onInterceptTouchEvent can be used to intercept event passing. OnInterceptTouchEvent returns true to disallow event passing to child views, false to disallow event passing to child Views. False is returned by default.
-
Events are distributed at dispatchTouch() of the ViewGroup, and the ViewGroup is handled as a View if the child View does not.
-
If the child View consumes the event passed, the ViewGroup will not receive any events.
If you want to further study also need to follow the source code to read a few times, can be combined with down and move events in various cases of analysis. I will also analyze the occurrence of the event later. If you find this article useful, please like and bookmark ✨.
The Android event distribution mechanism is the most comprehensive and easy to understand in history