Android中view的onTouch&onClick事件分發機制詳解

當view設定了setOnClickListener或setOnTouchListener之後，onClick或onTouch方法才會被調用，如下

mTextView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Logger.d(MainActivity.class," onClick");
            }
        });

        mTextView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                Logger.d(MainActivity.class," onTouch event :"+event.getAction());
                return false;
            }
        });
           

log如下：

使用自定義MyTextView，繼承TextView并重寫dispatchTouchEvent和onTouchEvent，log如下：

從log看調用順序依次為（如果手沒有抖，可能沒有ACTION_MOVE事件）

ACTION_DOWN:[email protected],MyTextView@dispatchTouchEvent,[email protected]，[email protected]

ACTION_MOVE:[email protected],MyTextView@dispatchTouchEvent,[email protected],[email protected]

ACTION_UP:[email protected],MyTextView@dispatchTouchEvent,[email protected],[email protected]

當[email protected]的event.getAction()為

MotionEvent.ACTION_UP時才調用onClick

注：單手或雙手操作觸摸螢幕事件，一般會有下面幾種

單手指操作：ACTION_DOWN(0) ACTION_MOVE(2) ACTION_UP(1)

多手指操作：ACTION_DOWN ACTION_POINTER_DOWN(5) ACTION_MOVE ACTION_POINTER_UP(6) ACTION_UP.

從上面的log可以看出是先執行TextView設定的onTouch，再調用對應的onClick方法的，Activity和控件都是先執行dispatchTouchEvent來分發touchEvent，下面我們來從源碼的角度，看下這個是怎麼實作的

frameworks/base/core/java/android/app/Activity.java
    public boolean dispatchTouchEvent(MotionEvent ev) {
        if (ev.getAction() == MotionEvent.ACTION_DOWN){
            onUserInteraction();
        }
        if (getWindow().superDispatchTouchEvent(ev)) {
            return true;
        }
        return onTouchEvent(ev);
    }
    public void onUserInteraction() {
    }
           

通過上面的方法可以看出，onUserInteraction方法在有目前activity捕獲到touchEvent的ACTION_DOWN事件時，會被觸發這個方法，說到了onUserInteraction，我們順便看看和它相關聯的一個方法onUserLeaveHint

onUserLeaveHint：當使用者按下 Home鍵，Activity#onUserLeaveHint()将會被回調。但是當來電導緻來電activity自動占據前台，Activity#onUserLeaveHint()将不會被回調。

onUserInteraction：目前activity有key, touch, or trackball event事件時都會調用，經常和onUserLeaveHint一起用來管理通知的。

接下來會調用getWindow().superDispatchTouchEvent(ev)，把touchEvent派遣給PhoneWindow（getWindow()傳回的是Window的執行個體，而PhoneWindow是Window唯一的孩子）

frameworks/base/core/java/com/android/internal/policy/PhoneWindow.java  
    @Override
    public boolean superDispatchKeyEvent(KeyEvent event) {
        return mDecor.superDispatchKeyEvent(event);
    }
           

在PhoneWindow裡繼續把事件傳遞給DecorView，從前一篇setContentView詳解中，我們知道了DecorView是所有視圖的根視圖，接下來看看DecorView裡的superDispatchKeyEvent

frameworks/base/core/java/com/android/internal/policy/DecorView.java
 public boolean superDispatchKeyEvent(KeyEvent event) {
    // Give priority to closing action modes if applicable.
    if (event.getKeyCode() == KeyEvent.KEYCODE_BACK) {
        final int action = event.getAction();
        // Back cancels action modes first.
        if (mPrimaryActionMode != null) {
            if (action == KeyEvent.ACTION_UP) {
                mPrimaryActionMode.finish();
            }
            return true;
        }
    }
    return super.dispatchKeyEvent(event);
}   
           

最後調用了父類的dispatchKeyEvent的，接着看看父類FrameLayout.java的dispatchKeyEvent，FrameLayout裡沒有定義這個方法，dispatchKeyEvent是從FrameLayout的父類ViewGroup.java裡擷取來，我們直接看這個方法

frameworks/base/core/java/android/view/ViewGroup.java
        public boolean dispatchTouchEvent(MotionEvent ev) {
        ...
        boolean handled = false;
        if (onFilterTouchEventForSecurity(ev)) {
            final int action = ev.getAction();
            final int actionMasked = action & MotionEvent.ACTION_MASK;

           ...
            // Check for interception.
            final boolean intercepted;
            if (actionMasked == MotionEvent.ACTION_DOWN
                    || mFirstTouchTarget != null) {
                final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != ;
                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;
            }

            // If intercepted, start normal event dispatch. Also if there is already
            // a view that is handling the gesture, do normal event dispatch.
            if (intercepted || mFirstTouchTarget != null) {
                ev.setTargetAccessibilityFocus(false);
            }

            // Check for cancelation.
            final boolean canceled = resetCancelNextUpFlag(this)
                    || actionMasked == MotionEvent.ACTION_CANCEL;
            ...
            TouchTarget newTouchTarget = null;
            boolean alreadyDispatchedToNewTouchTarget = false;
            if (!canceled && !intercepted) {
              ...
                  if (newTouchTarget == null && childrenCount != ) {
                        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<View> preorderedList = buildTouchDispatchChildList();
                        final boolean customOrder = preorderedList == null
                                && isChildrenDrawingOrderEnabled();
                        final View[] children = mChildren;
                        for (int i = childrenCount - ; i >= ; i--) {
                            final int childIndex = getAndVerifyPreorderedIndex(
                                    childrenCount, i, customOrder);
                            final View child = getAndVerifyPreorderedView(
                                    preorderedList, children, childIndex);
            // 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);
            } 

        return handled;
    }
           

在這個方法裡會依次調用onInterceptTouchEvent，擷取actionMasked是否為ACTION_CANCEL判斷是否中斷或取消事件的傳遞，通過buildTouchDispatchChildList來擷取自定義排序的視圖，對應的touchEvent将會被dispatch，通過dispatchTransformedTouchEvent把事件傳遞到對應view上

private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
            View child, int desiredPointerIdBits) {
        final boolean handled;

         ...
        // If the number of pointers is the same and we don't need to perform any fancy
        // irreversible transformations, then we can reuse the motion event for this
        // dispatch as long as we are careful to revert any changes we make.
        // Otherwise we need to make a copy.
        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);
        }

        // Perform any necessary transformations and dispatch.
        if (child == null) {
            handled = super.dispatchTouchEvent(transformedEvent);
        } else {
            final float offsetX = mScrollX - child.mLeft;
            final float offsetY = mScrollY - child.mTop;
            transformedEvent.offsetLocation(offsetX, offsetY);
            if (! child.hasIdentityMatrix()) {
                transformedEvent.transform(child.getInverseMatrix());
            }

            handled = child.dispatchTouchEvent(transformedEvent);
        }

        // Done.
        transformedEvent.recycle();
        return handled;
    }
           

這樣自定義的MyTextView中的dispatchTouchEvent就會被調用,這個方法是定義在View.java裡的，下面來看看具體實作

frameworks/base/core/java/android/view/View.java
    public boolean dispatchTouchEvent(MotionEvent event) {
          ...
        if (onFilterTouchEventForSecurity(event)) {
            if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
                result = true;
            }
            //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;
            }
        }
        ...
        return result;
    }

    boolean isAccessibilityFocusedViewOrHost() {
        return isAccessibilityFocused() || (getViewRootImpl() != null && getViewRootImpl()
                .getAccessibilityFocusedHost() == this);
    }
           

在這個方法裡面會先判斷目前view的OnTouchListener是否為null，目前view是否為enabled以及mOnTouchListener.onTouch傳回的結果來決定result的值，緊接着下面就用這個值來判斷是否需要調用view的onTouchEvent方法，隻有當result為false時，

onTouchEvent才會被調用，那麼onclick是在那被調用的呢，跟進去看看onTouchEvent的定義

frameworks/base/core/java/android/view/View.java
    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 & ENABLED_MASK) == DISABLED) {
            if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != ) {
                setPressed(false);
            }
            // A disabled view that is clickable still consumes the touch
            // events, it just doesn't respond to them.
            return (((viewFlags & CLICKABLE) == CLICKABLE
                    || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
                    || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
        }
        if (mTouchDelegate != null) {
            if (mTouchDelegate.onTouchEvent(event)) {
                return true;
            }
        }

        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) != ;
                    if ((mPrivateFlags & PFLAG_PRESSED) !=  || 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();
                                }
                            }
                        }
                       ...
                    }
            return true;
        }
        return false;
    }
           

當touchEvent的type為ACTION_UP時，裡面會調用performClick，進而在這個裡面調用注冊的click監聽

frameworks/base/core/java/android/view/View.java
    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;
    }
           

這樣我們就知道了OnClickListener和OnTouchListener的具體調用流程，以及onClick是在onTouch方法之後調用的，隻有onTouch傳回false時，onTouchEvent才會被調用，并且在onTouchEvent的getAction為ACTION_UP時調用performClick，處理OnClickListener，回調onClick方法。

另外需要注意的是，如果我們重寫[email protected]傳回false時，目前view的dispatchTouchEvent、 onTouchEvent，以及注冊的onTouch事件隻會在onTouchEvent的getAction為ACTION_DOWN時被調用一次，ACTION_MOVE和ACTION_UP事件都不會被調用

從上面log看[email protected]和

[email protected]隻在ACTION_DOWN時執行來一次，其實[email protected]裡根據 switch（action）裡每次都預設傳回裡true,這樣對應的ACTION_MOVE和ACTION_UP才會被調用

frameworks/base/core/java/android/view/View.java
public boolean onTouchEvent(MotionEvent event) {
   ...
   if (((viewFlags & CLICKABLE) == CLICKABLE ||
                (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
                (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
            switch (action) {
                case MotionEvent.ACTION_UP:
                    ...
                    break;
                case MotionEvent.ACTION_DOWN:
                    ...
                    break;
                case MotionEvent.ACTION_CANCEL:
                    ...
                    break;
                case MotionEvent.ACTION_MOVE:
                    ...
                    break;
            }
            return true;
        }
        return false;
    }