Android事件分发之View（一）

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1.View的dispatchTouchEvent:

/**
     * 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) {
        if (!onFilterTouchEventForSecurity(event)) {
            return false;
        }
        if (mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED &&
                mOnTouchListener.onTouch(this, event)) {
            return true;
        }
        return onTouchEvent(event);
    }

上述代码首先判断mOnTouchListener不为null，并且view是enable的状态，然后 mOnTouchListener.onTouch(this, event)返回true，这三个条件如果都满足，直接return true ; 也就是下面的onTouchEvent(event）不会被执行了；

2、onTouchEvent

  public boolean onTouchEvent(MotionEvent event) {
        final int viewFlags = mViewFlags;
        if ((viewFlags & ENABLED_MASK) == DISABLED) {
            return (((viewFlags & CLICKABLE) == CLICKABLE ||
                    (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE));
        }
        //如果设置了Touch代理，就交给代理来处理，mTouchDelegate默认是null
        if (mTouchDelegate != null) {
            if (mTouchDelegate.onTouchEvent(event)) {
                return true;
            }
        }
        //如果View是clickable或者longClickable的onTouchEvent就返回true, 否则返回false
        if (((viewFlags & CLICKABLE) == CLICKABLE ||
                (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
               ……
            return true;
        }
        return false;
    }

以上基于2.2版本的SDK代码

一个clickable或者longclickable的View是一直消费Touch事件的，不管它是否enable。如果clickable或者longclickable，onTouchEvent会直接返回true，表示该view会直接消费TouchEvent事件。而一般的View既不是clickable也不是longclickable的(即不会消费Touch事件，只会执行ACTION_DOWN而不会执行ACTION_MOVE和ACTION_UP) Button是clickable的，可以消费Touch事件，但是我们可以通过setClickable()和setLongClickable()来设置View是否为clickable和longClickable。当然还可以通过重写View的onTouchEvent()方法来控制Touch事件的消费与否。

长按事件是在DOWN中执行的，点击事件是在UP中执行的。想要执行点击事件的前提是消费了ACTION_DOWN和ACTION_MOVE,并且没有设置OnLongClickListener的情况下，如设置了OnLongClickListener的情况，则必须使onLongClick()返回false

DOWN时：

                case MotionEvent.ACTION_DOWN:
                    if (mPendingCheckForTap == null) {
                        mPendingCheckForTap = new CheckForTap();
                    }
                    mPrivateFlags |= PREPRESSED;
                    mHasPerformedLongPress = false;
                    postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
                    break;

a、首先设置标志为PREPRESSED，设置mHasPerformedLongPress=false ;然后发出一个115ms后的mPendingCheckForTap；到达延时时间后执行CheckForTap

  private final class CheckForTap implements Runnable {
        public void run() {
            mPrivateFlags &= ~PREPRESSED;
            mPrivateFlags |= PRESSED;
            refreshDrawableState();
            if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) {
                //检测长按
                postCheckForLongClick(ViewConfiguration.getTapTimeout());
            }
        }
    }

b、如果115ms内没有触发UP，则将标志置为PRESSED，清除PREPRESSED标志，同时发出一个延时为500-115ms的，检测长按任务消息；

 private void postCheckForLongClick(int delayOffset) {
        mHasPerformedLongPress = false;
        if (mPendingCheckForLongPress == null) {
            mPendingCheckForLongPress = new CheckForLongPress();
        }
        mPendingCheckForLongPress.rememberWindowAttachCount();
        postDelayed(mPendingCheckForLongPress,
                ViewConfiguration.getLongPressTimeout() - delayOffset);
    }

class CheckForLongPress implements Runnable {
        private int mOriginalWindowAttachCount;
        public void run() {
            if (isPressed() && (mParent != null)
                    && mOriginalWindowAttachCount == mWindowAttachCount) {
                if (performLongClick()) {
                    mHasPerformedLongPress = true;
                }
            }
        }

c、如果500ms内（从DOWN触发开始算），则会触发LongClickListener:此时如果LongClickListener不为null，则会执行回调，8-10行，同时如果LongClickListener.onClick返回true，才把mHasPerformedLongPress设置为true;否则mHasPerformedLongPress依然为false;

MOVE时：

case MotionEvent.ACTION_MOVE:
                    final int x = (int) event.getX();
                    final int y = (int) event.getY();
                    // Be lenient about moving outside of buttons
                    int slop = mTouchSlop;
                    if ((x < 0 - slop) || (x >= getWidth() + slop) ||
                            (y < 0 - slop) || (y >= getHeight() + slop)) {
                        // Outside button
                        removeTapCallback();
                        if ((mPrivateFlags & PRESSED) != 0) {
                            // Remove any future long press/tap checks
                            removeLongPressCallback();
                            // Need to switch from pressed to not pressed
                            mPrivateFlags &= ~PRESSED;
                            refreshDrawableState();
                        }
                    }
                    break;

主要就是检测用户是否划出控件，如果划出了：

115ms内，直接移除mPendingCheckForTap；

115ms后，则将标志中的PRESSED去除，同时移除长按的检查：removeLongPressCallback();

UP时：

case MotionEvent.ACTION_UP:
                    boolean prepressed = (mPrivateFlags & PREPRESSED) != 0;
                    if ((mPrivateFlags & 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 (!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) {
                            mPrivateFlags |= PRESSED;
                            refreshDrawableState();
                            postDelayed(mUnsetPressedState,
                                    ViewConfiguration.getPressedStateDuration());
                        } else if (!post(mUnsetPressedState)) {
                            // If the post failed, unpress right now
                            mUnsetPressedState.run();
                        }
                        removeTapCallback();
                    }
                    break;

a、如果115ms内，触发UP，此时标志为PREPRESSED，则执行UnsetPressedState，setPressed(false);会把setPress转发下去，可以在View中复写dispatchSetPressed方法接收；

b、如果是115ms-500ms间，即长按还未发生，则首先移除长按检测，执行onClick回调；

c、如果是500ms以后，那么有两种情况：

i.设置了onLongClickListener，且onLongClickListener.onClick返回true，则点击事件OnClick事件无法触发；

ii.没有设置onLongClickListener或者onLongClickListener.onClick返回false，则点击事件OnClick事件依然可以触发（mHasPerformedLongPress为false，UP的时候执行28行的if语句，开始执行点击事件）；

 if (!mHasPerformedLongPress) {
                            removeLongPressCallback();
                            if (!focusTaken) {
                                if (mPerformClick == null) {
                                    mPerformClick = new PerformClick();
                                }
                                if (!post(mPerformClick)) {
                                    performClick();
                                }
                            }
                        }

d、最后执行mUnsetPressedState.run()，将setPressed传递下去，然后将PRESSED标识去除；

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