在安卓中如果我们需要点击一个控件，并做处理的话，首先想到的就是setOnClickListener方法和setOnTouchListener方法，而在自定义控件中，需要自己处理触摸事件的话，我们需要改写onTouchEvent方法。这些方法的执行顺序和怎么被调用的，就是今天的研究课题
首先自定义一个控件，并改写onTouchEvent方法，打印日志
/*** 测试事件分发顺序*/
public class MyView extends View {public static final String TAG = MyView.class.getSimpleName();public MyView(Context context) {this(context, null);}public MyView(Context context, @Nullable AttributeSet attrs) {this(context, attrs, 0);}public MyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);}@Overridepublic boolean onTouchEvent(MotionEvent event) {Log.i(TAG, "onTouchEvent " + event.getAction());return super.onTouchEvent(event);}
}
public class MainActivity extends AppCompatActivity {private static final String TAG = MainActivity.class.getSimpleName();@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);MyView my_test = findViewById(R.id.my_test);my_test.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Log.i(MyView.TAG, "onClick");}});my_test.setOnTouchListener(new View.OnTouchListener() {@Overridepublic boolean onTouch(View v, MotionEvent event) {Log.i(MyView.TAG, "onTouch "+event.getAction());return false;}});}
}
打印日志如下：
2020-02-08 16:09:51.594 11907-11907/com.aruba.touchapplication I/MyView: onTouch 0
2020-02-08 16:09:51.595 11907-11907/com.aruba.touchapplication I/MyView: onTouchEvent 0
2020-02-08 16:09:51.610 11907-11907/com.aruba.touchapplication I/MyView: onTouch 2
2020-02-08 16:09:51.610 11907-11907/com.aruba.touchapplication I/MyView: onTouchEvent 2
2020-02-08 16:09:51.637 11907-11907/com.aruba.touchapplication I/MyView: onTouch 2
2020-02-08 16:09:51.637 11907-11907/com.aruba.touchapplication I/MyView: onTouchEvent 2
2020-02-08 16:09:51.639 11907-11907/com.aruba.touchapplication I/MyView: onTouch 1
2020-02-08 16:09:51.639 11907-11907/com.aruba.touchapplication I/MyView: onTouchEvent 1
2020-02-08 16:09:51.641 11907-11907/com.aruba.touchapplication I/MyView: onClick
查看源码发现，0代表按下，1代表抬起，2代表移动
public static final int ACTION_DOWN = 0;
public static final int ACTION_UP = 1;
public static final int ACTION_MOVE = 2;
所以一个控件触摸事件的顺序是先调用onTouch方法，再调用onTouchEvent方法，最后调用onClick方法，至于原因，接下来我们将分析源码
我们来到View的dispatchTouchEvent方法
/*** Pass the touch screen motion event down to the target view, or this* view if it is the target.** @param event The motion event to be dispatched.* @return True if the event was handled by the view, false otherwise.*/public boolean dispatchTouchEvent(MotionEvent event) {//AccessibilityService是辅助残疾人士使用手机的功能，可以模拟触摸事件，首先在事件分发前，//会判断是否是模拟触摸事件// If the event should be handled by accessibility focus first.if (event.isTargetAccessibilityFocus()) {// We don't have focus or no virtual descendant has it, do not handle the event.if (!isAccessibilityFocusedViewOrHost()) {return false;}// We have focus and got the event, then use normal event dispatch.event.setTargetAccessibilityFocus(false);}boolean result = false;if (mInputEventConsistencyVerifier != null) {mInputEventConsistencyVerifier.onTouchEvent(event, 0);}final int actionMasked = event.getActionMasked();if (actionMasked == MotionEvent.ACTION_DOWN) {// Defensive cleanup for new gesturestopNestedScroll();}//安全检测，一般都是trueif (onFilterTouchEventForSecurity(event)) {if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {result = true;}//noinspection SimplifiableIfStatementListenerInfo li = mListenerInfo;//这边会判断是否设置了OnTouchListener，如果设置了，并在回调时返回了ture，将result赋值成trueif (li != null && li.mOnTouchListener != null&& (mViewFlags & ENABLED_MASK) == ENABLED&& li.mOnTouchListener.onTouch(this, event)) {result = true;}//如果上面result为true了(mOnTouchListener.onTouch方法返回true)，则不会调用onTouchEvent方法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;}
在这边我们发现，View会先调用OnTouchListener的onTouch方法，然后再调用OnTouchEvent方法，再看OnTouchEvent方法
public boolean onTouchEvent(MotionEvent event) {final float x = event.getX();final float y = event.getY();final int viewFlags = mViewFlags;final int action = event.getAction();final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;if ((viewFlags & ENABLED_MASK) == DISABLED) {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.return clickable;}if (mTouchDelegate != null) {if (mTouchDelegate.onTouchEvent(event)) {return true;}}if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {switch (action) {case MotionEvent.ACTION_UP:mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;if ((viewFlags & TOOLTIP) == TOOLTIP) {handleTooltipUp();}if (!clickable) {removeTapCallback();removeLongPressCallback();mInContextButtonPress = false;mHasPerformedLongPress = false;mIgnoreNextUpEvent = false;break;}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 checkremoveLongPressCallback();// Only perform take click actions if we were in the pressed stateif (!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();}//关键代码if (!post(mPerformClick)) {performClickInternal();}}}if (mUnsetPressedState == null) {mUnsetPressedState = new UnsetPressedState();}if (prepressed) {postDelayed(mUnsetPressedState,ViewConfiguration.getPressedStateDuration());} else if (!post(mUnsetPressedState)) {// If the post failed, unpress right nowmUnsetPressedState.run();}removeTapCallback();}mIgnoreNextUpEvent = false;break;case MotionEvent.ACTION_DOWN:if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) {mPrivateFlags3 |= PFLAG3_FINGER_DOWN;}mHasPerformedLongPress = false;if (!clickable) {checkForLongClick(0, x, y);break;}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 awaysetPressed(true, x, y);checkForLongClick(0, x, y);}break;case MotionEvent.ACTION_CANCEL:if (clickable) {setPressed(false);}removeTapCallback();removeLongPressCallback();mInContextButtonPress = false;mHasPerformedLongPress = false;mIgnoreNextUpEvent = false;mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;break;case MotionEvent.ACTION_MOVE:if (clickable) {drawableHotspotChanged(x, y);}// Be lenient about moving outside of buttonsif (!pointInView(x, y, mTouchSlop)) {// Outside button// Remove any future long press/tap checksremoveTapCallback();removeLongPressCallback();if ((mPrivateFlags & PFLAG_PRESSED) != 0) {setPressed(false);}mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;}break;}return true;}return false;}
发现在MotionEvent.ACTION_UP时，会调用到performClickInternal方法，而performClickInternal方法就是调用了performClick方法
private boolean performClickInternal() {// Must notify autofill manager before performing the click actions to avoid scenarios where// the app has a click listener that changes the state of views the autofill service might// be interested on.notifyAutofillManagerOnClick();return performClick();}
public boolean performClick() {// We still need to call this method to handle the cases where performClick() was called// externally, instead of through performClickInternal()notifyAutofillManagerOnClick();final boolean result;final ListenerInfo li = mListenerInfo;//如果mOnClickListener不为空，则调用mOnClickListener的onClick方法///mOnClickListener就是我们调用setOnClickListener传入的参数if (li != null && li.mOnClickListener != null) {playSoundEffect(SoundEffectConstants.CLICK);li.mOnClickListener.onClick(this);result = true;} else {result = false;}sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);notifyEnterOrExitForAutoFillIfNeeded(true);return result;}
到此，我们知道了为什么onTouch会先执行，onTouchEvent会后执行，并且为什么手指抬起后才会执行onClick方法