android开发中的OnTouch onClick onTouchEvent研究

来源：互联网发布：织田信忠知乎编辑：程序博客网时间：2024/06/10 11:38

今天面试的时候有人问到了这个问题，当时一下没想起来，想这回来就研究一下，所以自己写了一个小demo

这个是我的layout的布局

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public class MyLayout extends LinearLayout implements View.OnClickListener, View.OnTouchListener {    public MyLayout(Context context) {        super(context);        Log.d(TAG,"MyLayout init");    }    public MyLayout(Context context, AttributeSet attrs) {        super(context, attrs);        setOnClickListener(this);        setOnTouchListener(this);    }    @Override    public void onClick(View v) {        Log.d(TAG,"MyFrameLayout onClick");    }    @Override    public boolean onTouch(View v, MotionEvent event) {        Log.d(TAG,"MyLayout onTouch");        return false;    }    @Override    public boolean dispatchTouchEvent(MotionEvent event) {        Log.d(TAG,"MyLayout dispatchTouchEvent");        return super.dispatchTouchEvent(event);    }    @Override    public boolean onTouchEvent(MotionEvent event) {        Log.d(TAG,"MyLayout onTouchEvent"+event.getAction());        return super.onTouchEvent(event);    }}

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这个是我的button布局

public class FButton extends Button implements View.OnClickListener, View.OnTouchListener {    public FButton(Context context) {        super(context);        Log.d(TAG,"FButton init");    }    public FButton(Context context, AttributeSet attrs) {        super(context, attrs);        setOnClickListener(this);        setOnTouchListener(this);    }    @Override    public boolean dispatchTouchEvent(MotionEvent event) {        Log.d(TAG,"FButton dispatchTouchEvent");        return super.dispatchTouchEvent(event);    }    @Override    public boolean onTouchEvent(MotionEvent event) {        Log.d(TAG,"FButton onTouchEvent=="+event.getAction());        return super.onTouchEvent(event);    }    @Override    public void onClick(View v) {        Log.d(TAG,"FButton onClick");    }    @Override    public boolean onTouch(View v, MotionEvent event) {        Log.d(TAG,"FButton onTouch");        return false;    }}

我在Acitivity的布局中引用了这两个布局

然后点击button，出现如下的log，可以看到如下的输出

我们从打印结果可以直观看到，点击Button按钮事件分发过程如下 dispatchTouchEvent---->onTouch---->onTouchEvent----->onClick。并且如果仔细的你会发现，都是在ACTION_UP事件之后才触发onClick点击事件，为什么会是这样？？现在我们不得而知。我们仅仅是从打印结果推测事件分发的结论，现在我们从源码分析下这个事件分发流程为什么是这样子。

这个是View的 dispatchTouchEvent 方法的源码

public boolean dispatchTouchEvent(MotionEvent event) {    // 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 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;}

关键在于li.mOnTouchListener.onTouch(this, event) 的返回值，这个接口回调就是我们外面写的myButton.setOnTouchListener事件（Button 的onTouch事件）

在MainActivity代码里，我们setOnTouchListener返回的值是false，所以在源码中我们可以看到 17行的条件不成立，那么条件不成立，result=false；

因此，源码的第23行if 判断第一个条件成立，继续执行第二个条件，也就是onTouchEvent。我们跳到这个方法里看看里面干啥了？看如下代码：

public boolean onTouchEvent(MotionEvent event) {        if (((viewFlags & CLICKABLE) == CLICKABLE ||                (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {            switch (event.getAction()) {                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) {                            // 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();                    }                    break;            return true;        }        return false;    }

在标红的方法里，执行了点击事件的回调

public boolean performClick() {    final boolean result;    final ListenerInfo li = mListenerInfo;    if (li != null && li.mOnClickListener != null) {        playSoundEffect(SoundEffectConstants.CLICK);        li.mOnClickListener.onClick(this);        result = true;    } else {        result = false;    }    sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);    return result;}

到此为止，我们从源码分析了Button事件分发过程
结论：dispatchTouchEvent---->onTouch---->onTouchEvent----->onClick。

并且如果仔细的你会发现，是在所有ACTION_UP事件之后才触发onClick点击事件。

我有一部分借鉴了别人的博客，再写上一些自己的心得体会，onTouch是绑定了监听器的方法，这个优先级别最高，如果在这个方法里返回了ture，后面的onTouchEvent与

onClick就不会执行。

因此，事件分发之间的关系是：dispatchTouchEvent方法中线执行 onTouch接口回调，然后根据onTouch方法的返回值判断是否执行onTouchEvent方法，onTouchEvent方法中执行了onClick接口回调。

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