Android Touch事件传递机制详解 上

尊重原创：http://blog.csdn.net/yuanzeyao/article/details/37961997

       最近总是遇到关于Android Touch事件的问题，如：滑动冲突的问题，以前也花时间学习过Android Touch事件的传递机制，可以每次用起来的时候总是忘记了，索性自己总结一下写篇文章避免以后忘记了，其实网上关于Touch事件的传递的文章真的很多，但是很少有系统性的，都是写了一个简单的demo运行了一下，对于我们了解Android Touch事件基本上没有任何帮助。

       我就把事件的始点定在PhoneWindow中的DecorView吧，至于是谁把事件传递给DecorView的我们先不用去关心它。（如果想深入研究，请阅读我的另外一篇文章Android中按键事件传递机制）我们只需要知道它的上家是通过dispatchTouchEvent方法将事件分发给DecorView就行了，我进入到该方法瞧瞧究竟。

在阅读之前最好阅读Android窗口创建过程

@Override
        public boolean dispatchTouchEvent(MotionEvent ev) 
	{
	    //该Callback就是该DecorView附属的Activity,可以看我的另外一篇文章《Android中窗口的创建过程》
            final Callback cb = getCallback();
	    //如果cb!=null && mFeatureId<0 就执行Activity中的dispatchTouchEvent方法，对于应用程序窗口 <span style="white-space:pre">			</span>    //这两个条件一般是满足的
            return cb != null && mFeatureId < 0 ? cb.dispatchTouchEvent(ev) : super
                    .dispatchTouchEvent(ev);
        }

 public boolean dispatchTouchEvent(MotionEvent ev) {
        if (ev.getAction() == MotionEvent.ACTION_DOWN) {
            onUserInteraction();
        }
	//getWindow返回什么？如果阅读过我的《Android中窗口创建过程》的都知道就是PhoneWindow,如果PhoneWindow中的superDispatchTouchEvent方法返回了true,
	//那么该Touch事件就被PhoneWindow给消费掉了，不会再继续传递，如果返回false，那么就会执行Activity的onTouchEvent方法
        if (getWindow().superDispatchTouchEvent(ev)) {
            return true;
        }
        return onTouchEvent(ev);
    }

@Override
    public boolean superDispatchTouchEvent(MotionEvent event) {
		//mDecor是一个DecorView类型变量
        return mDecor.superDispatchTouchEvent(event);
    }

public boolean superDispatchTouchEvent(MotionEvent event) {
			//直接调用父类的dispatchTouchEvent方法
            return super.dispatchTouchEvent(event);
        }

@Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        final int action = ev.getAction();
        final float xf = ev.getX();
        final float yf = ev.getY();
        final float scrolledXFloat = xf + mScrollX;
        final float scrolledYFloat = yf + mScrollY;
        final Rect frame = mTempRect;
		//可以通过requestDisallowInterceptTouchEvent方法来设置该变量的值，通常是false
        boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;

        if (action == MotionEvent.ACTION_DOWN) {
            if (mMotionTarget != null) {
                // this is weird, we got a pen down, but we thought it was
                // already down!
                // XXX: We should probably send an ACTION_UP to the current
                // target.
                mMotionTarget = null;
            }
            // If we're disallowing intercept or if we're allowing and we didn't
            // intercept
			//onInterceptTouchEvent在默认情况下是返回false的，所以这里通常是可以进去的
            if (disallowIntercept || !onInterceptTouchEvent(ev)) {
                // reset this event's action (just to protect ourselves)
                ev.setAction(MotionEvent.ACTION_DOWN);
                // We know we want to dispatch the event down, find a child
                // who can handle it, start with the front-most child.
                final int scrolledXInt = (int) scrolledXFloat;
                final int scrolledYInt = (int) scrolledYFloat;
                final View[] children = mChildren;
                final int count = mChildrenCount;
				//遍历ViewGroup的孩子，如果触摸点在某一个子View中，则调用在子View的dispatchTouchEvent
                for (int i = count - 1; i >= 0; i--) {
                    final View child = children[i];
                    if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE
                            || child.getAnimation() != null) {
                        child.getHitRect(frame);
                        if (frame.contains(scrolledXInt, scrolledYInt)) {
                            // offset the event to the view's coordinate system
                            final float xc = scrolledXFloat - child.mLeft;
                            final float yc = scrolledYFloat - child.mTop;
                            ev.setLocation(xc, yc);
                            child.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
				//调用了某一个子View 的dispatchTouchEvent ，如果这个子View 的dispatchTouchEvent返回true,那么意味着这个事件
				//已经被这个子View消费了，不会继续传递
                            if (child.dispatchTouchEvent(ev))  {
                                // Event handled, we have a target now.
                                mMotionTarget = child;
                                return true;
                            }
                            // The event didn't get handled, try the next view.
                            // Don't reset the event's location, it's not
                            // necessary here.
                        }
                    }
                }
            }
        }

        boolean isUpOrCancel = (action == MotionEvent.ACTION_UP) ||
                (action == MotionEvent.ACTION_CANCEL);

        if (isUpOrCancel) {
            // Note, we've already copied the previous state to our local
            // variable, so this takes effect on the next event
            mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
        }

        // The event wasn't an ACTION_DOWN, dispatch it to our target if
        // we have one.
        final View target = mMotionTarget;
		//对于一个Action_down事件，如果走到了这里，说明所有的子View 都没有消费掉这个事件，那么它就调用父类的
		//的dispatchTouchEvnet方法，ViewGroup的父类就是View
        if (target == null) {
            // We don't have a target, this means we're handling the
            // event as a regular view.
            ev.setLocation(xf, yf);
            if ((mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {
                ev.setAction(MotionEvent.ACTION_CANCEL);
                mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
            }
            return super.dispatchTouchEvent(ev);
        }

        // if have a target, see if we're allowed to and want to intercept its
        // events
        if (!disallowIntercept && onInterceptTouchEvent(ev)) {
            final float xc = scrolledXFloat - (float) target.mLeft;
            final float yc = scrolledYFloat - (float) target.mTop;
            mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
            ev.setAction(MotionEvent.ACTION_CANCEL);
            ev.setLocation(xc, yc);
            if (!target.dispatchTouchEvent(ev)) {
                // target didn't handle ACTION_CANCEL. not much we can do
                // but they should have.
            }
            // clear the target
            mMotionTarget = null;
            // Don't dispatch this event to our own view, because we already
            // saw it when intercepting; we just want to give the following
            // event to the normal onTouchEvent().
            return true;
        }

        if (isUpOrCancel) {
            mMotionTarget = null;
        }

        // finally offset the event to the target's coordinate system and
        // dispatch the event.
        final float xc = scrolledXFloat - (float) target.mLeft;
        final float yc = scrolledYFloat - (float) target.mTop;
        ev.setLocation(xc, yc);

        if ((target.mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {
            ev.setAction(MotionEvent.ACTION_CANCEL);
            target.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
            mMotionTarget = null;
        }

        return target.dispatchTouchEvent(ev);
    }

public boolean onInterceptTouchEvent(MotionEvent ev) {
        return false;
    }

对于任何一款Android应用，展现给用户最上面的通常就是一个View，如Button,ImageView等等，也就是说一些触摸事件最终都是传递给了这个控件，如果控件消费了这些事件，那么就停止传递了，如果没有消费，那么就交给控件所属ViewGroup的onTouchEvnet处理，我们就看看View的dispatchTouchEvent方法吧

public boolean dispatchTouchEvent(MotionEvent event) {
        if (mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED &&
                mOnTouchListener.onTouch(this, event)) {
            return true;
        }
        return onTouchEvent(event);
    }

 public void setOnTouchListener(OnTouchListener l) {
        mOnTouchListener = l;
    }

public boolean onTouchEvent(MotionEvent event) {
        final int viewFlags = mViewFlags;
		//(A)
        if ((viewFlags & ENABLED_MASK) == DISABLED) {
            // 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));
        }

        if (mTouchDelegate != null) {
            if (mTouchDelegate.onTouchEvent(event)) {
                return true;
            }
        }
		//(B)
        if (((viewFlags & CLICKABLE) == CLICKABLE ||
                (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
            switch (event.getAction()) {
                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();
                                }
								//(C)
                                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;

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

                case MotionEvent.ACTION_CANCEL:
                    mPrivateFlags &= ~PRESSED;
                    refreshDrawableState();
                    removeTapCallback();
                    break;

                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;
            }
			//(D)
            return true;
        }

        return false;
    }

Android Touch事件传递机制详解 上,,5-wow.com