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Android Touch事件传递机制引发的血案

作者:AG88    发布时间: 2019-02-01

Android Touch事件传递机制引发的血案

Android Touch事件传递机制引发的血案

 

关于Android Touch事件传递机制我之前也写过两篇文章,自认为对Touche事件还是理解得比较清楚的,但是最近遇到的一个问题,让我再次对Android Touche事件进行一次学习。

我的关于Android Touche事件传递机制的文章如下:

http://blog.csdn.net/yuanzeyao/article/details/37961997

http://blog.csdn.net/yuanzeyao/article/details/38025165

 

我在这两篇文章中得出过以下结论:

1、如果一个view是clickable的,那么这个View的onTouchEvent是一定会返回true的,也就是说任何触摸事件都会被消费掉

2、如果一个View对于ACTION_DOWN事件没有消费掉(onTouchEvent 返回false),那么后续的ACTION_MOVE,ACTION_UP是都不会接受到的,也就是没有机会处理这些事件,这些事件都是在父View里面给处理了

3、如果一个ViewGroup想要拦截事件(不让事件传递到子View),那么它只需要改写ViewGroup的onInterceptTouchEvent(MotionEvent ev) 方法,让他返回true,或者调用requestDisallowInterceptTouchEvent(true);

4、Android中的Touche事件是从底层向上层传递的 Activity->DecorView->ViewGroup->View

 

理解了上面的问题,我们就开始看看我所遇到的问题吧,

在使用SlideMenu的时候,在中的Activity中仅仅放置一个TextView,你会发现SlideMenu无法滑动,当时通过顶部的Title可以滑动,由于对SlideMenu用的不是很熟,当时以为是SlideMenu的哪个属性用错了,后来一直没有解决问题,直到一位网友说设置TextView的clickable为true就可以解决问题,我尝试了一下,还真行!哈哈。。。,这个里面的原因你理解了吗?如果没有理解,请继续往下看

 

按照我之前对Touche事件的理解,如果设置clickable,那么Touche事件肯定就被TextView给消费掉了,如果被TextView消费掉了,那么SlideMenu如何实现滑动?要解开这个问题答案,还是看看SlideMenu的源码吗

 

我们首先看看SlideMenu中CustomViewAbove和Touche有关的方法

 

@Override
	public boolean onInterceptTouchEvent(MotionEvent ev) {

		if (!mEnabled)
			return false;

		final int action = ev.getAction() & MotionEventCompat.ACTION_MASK;

		if (action == MotionEvent.ACTION_DOWN && DEBUG)
			Log.v(TAG, Received ACTION_DOWN);

		if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP
				|| (action != MotionEvent.ACTION_DOWN && mIsUnableToDrag)) {
			endDrag();
			return false;
		}

		switch (action) {
		case MotionEvent.ACTION_MOVE:
			try{
				final int activePointerId = mActivePointerId;
				if (activePointerId == INVALID_POINTER)
					break;
				final int pointerIndex = this.getPointerIndex(ev, activePointerId);
				final float x = MotionEventCompat.getX(ev, pointerIndex);
				final float dx = x - mLastMotionX;
				final float xDiff = Math.abs(dx);
				final float y = MotionEventCompat.getY(ev, pointerIndex);
				final float yDiff = Math.abs(y - mLastMotionY);
				if (DEBUG) Log.v(TAG, onInterceptTouch moved to:( + x + ,  + y + ), diff:( + xDiff + ,  + yDiff + ), mLastMotionX: + mLastMotionX);
				if (xDiff > mTouchSlop && xDiff > yDiff && thisSlideAllowed(dx)) {
					if (DEBUG) Log.v(TAG, Starting drag! from onInterceptTouch);
					startDrag();
					mLastMotionX = x;
					setScrollingCacheEnabled(true);
				} else if (yDiff > mTouchSlop) {
					mIsUnableToDrag = true;
				}
			}
			catch(IllegalArgumentException e)
			{
				e.printStackTrace();
			}
			break;

		case MotionEvent.ACTION_DOWN:
			mActivePointerId = ev.getAction() & ((Build.VERSION.SDK_INT >= 8) ? MotionEvent.ACTION_POINTER_INDEX_MASK : 
				MotionEvent.ACTION_POINTER_INDEX_MASK);
			mLastMotionX = mInitialMotionX = MotionEventCompat.getX(ev, mActivePointerId);
			mLastMotionY = MotionEventCompat.getY(ev, mActivePointerId);
			if (thisTouchAllowed(ev)) {
				mIsBeingDragged = false;
				mIsUnableToDrag = false;
				if (isMenuOpen() && mViewBehind.menuTouchInQuickReturn(mContent, mCurItem, ev.getX() + mScrollX)) {
					mQuickReturn = true;
				}
			} else {
				mIsUnableToDrag = true;
			}
			break;
		case MotionEventCompat.ACTION_POINTER_UP:
			onSecondaryPointerUp(ev);
			break;
		}

		if (!mIsBeingDragged) {
			if (mVelocityTracker == null) {
				mVelocityTracker = VelocityTracker.obtain();
			}
			mVelocityTracker.addMovement(ev);
		}
		return mIsBeingDragged || mQuickReturn;
	}

看看这个方法,这个方法里面有个逻辑就是当滑动到一定距离,就会返回true,也就是说会拦截滑动事件,第一个ACTION_DOWN肯定不会拦截。

 

再看看onToucheEvent.java

 

	@Override
	public boolean onTouchEvent(MotionEvent ev) {

		if (!mEnabled)
			return false;

		//		if (!mIsBeingDragged && !thisTouchAllowed(ev))
		//			return false;

		if (!mIsBeingDragged && !mQuickReturn)
			return false;

		final int action = ev.getAction();

		if (mVelocityTracker == null) {
			mVelocityTracker = VelocityTracker.obtain();
		}
		mVelocityTracker.addMovement(ev);

		switch (action & MotionEventCompat.ACTION_MASK) {
		case MotionEvent.ACTION_DOWN:
			/*
			 * If being flinged and user touches, stop the fling. isFinished
			 * will be false if being flinged.
			 */
			completeScroll();

			// Remember where the motion event started
			mLastMotionX = mInitialMotionX = ev.getX();
			mActivePointerId = MotionEventCompat.getPointerId(ev, 0);
			break;
		case MotionEvent.ACTION_MOVE:
			if (!mIsBeingDragged) {				
				if (mActivePointerId == INVALID_POINTER)
					break;
				final int pointerIndex = getPointerIndex(ev, mActivePointerId);
				final float x = MotionEventCompat.getX(ev, pointerIndex);
				final float dx = x - mLastMotionX;
				final float xDiff = Math.abs(dx);
				final float y = MotionEventCompat.getY(ev, pointerIndex);
				final float yDiff = Math.abs(y - mLastMotionY);
				if (DEBUG) Log.v(TAG, onTouch moved to:( + x + ,  + y + ), diff:( + xDiff + ,  + yDiff + )
mIsBeingDragged: + mIsBeingDragged + , mLastMotionX: + mLastMotionX);
				if ((xDiff > mTouchSlop || (mQuickReturn && xDiff > mTouchSlop / 4))
						&& xDiff > yDiff && thisSlideAllowed(dx)) {
					if (DEBUG) Log.v(TAG, Starting drag! from onTouch);
					startDrag();
					mLastMotionX = x;
					setScrollingCacheEnabled(true);
				} else {
					if (DEBUG) Log.v(TAG, onTouch returning false);
					return false;
				}
			}
			if (mIsBeingDragged) {
				// Scroll to follow the motion event
				final int activePointerIndex = getPointerIndex(ev, mActivePointerId);
				if (mActivePointerId == INVALID_POINTER) {
					break;
				}
				final float x = MotionEventCompat.getX(ev, activePointerIndex);
				final float deltaX = mLastMotionX - x;
				mLastMotionX = x;
				float oldScrollX = getScrollX();
				float scrollX = oldScrollX + deltaX;
				final float leftBound = getLeftBound();
				final float rightBound = getRightBound();
				if (scrollX < leftBound) {
					scrollX = leftBound;
				} else if (scrollX > rightBound) {
					scrollX = rightBound;
				}
				// Don't lose the rounded component
				mLastMotionX += scrollX - (int) scrollX;
				scrollTo((int) scrollX, getScrollY());
				pageScrolled((int) scrollX);
			}
			break;
		case MotionEvent.ACTION_UP:
			if (mIsBeingDragged) {
				final VelocityTracker velocityTracker = mVelocityTracker;
				velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
				int initialVelocity = (int) VelocityTrackerCompat.getXVelocity(
						velocityTracker, mActivePointerId);
				final int scrollX = getScrollX();
				//				final int widthWithMargin = getWidth();
				//				final float pageOffset = (float) (scrollX % widthWithMargin) / widthWithMargin;
				// TODO test this. should get better flinging behavior
				final float pageOffset = (float) (scrollX - getDestScrollX(mCurItem)) / getBehindWidth();
				final int activePointerIndex = getPointerIndex(ev, mActivePointerId);
				if (mActivePointerId != INVALID_POINTER) {
					final float x = MotionEventCompat.getX(ev, activePointerIndex);
					final int totalDelta = (int) (x - mInitialMotionX);
					int nextPage = determineTargetPage(pageOffset, initialVelocity, totalDelta);
					setCurrentItemInternal(nextPage, true, true, initialVelocity);
				} else {	
					setCurrentItemInternal(mCurItem, true, true, initialVelocity);
				}
				mActivePointerId = INVALID_POINTER;
				endDrag();
			} else if (mQuickReturn && mViewBehind.menuTouchInQuickReturn(mContent, mCurItem, ev.getX() + mScrollX)) {
				// close the menu
				setCurrentItem(1);
				endDrag();
			}
			break;
		case MotionEvent.ACTION_CANCEL:
			if (mIsBeingDragged) {
				setCurrentItemInternal(mCurItem, true, true);
				mActivePointerId = INVALID_POINTER;
				endDrag();
			}
			break;
		case MotionEventCompat.ACTION_POINTER_DOWN: {
			final int index = MotionEventCompat.getActionIndex(ev);
			final float x = MotionEventCompat.getX(ev, index);
			mLastMotionX = x;
			mActivePointerId = MotionEventCompat.getPointerId(ev, index);
			break;
		}
		case MotionEventCompat.ACTION_POINTER_UP:
			onSecondaryPointerUp(ev);
			int pointerIndex = this.getPointerIndex(ev, mActivePointerId);
			if (mActivePointerId == INVALID_POINTER)
				break;
			mLastMotionX = MotionEventCompat.getX(ev, pointerIndex);
			break;
		}
		return true;
	}

我们重点观察ACTION_DWON事件,对于ACTION_DWON事件,SlideMenu是没有拦截的,所以传递到了TextView,由于默认TextView是没有clickable的,所以是不会消费这个事件,如果TextView不消费,那么事件就传递到了SlideMenu,但是我们发现在SlideMenu中也没有消费这个事件,还记得我们上面的结论2吗,根据结论2,我们知道后面的事件是传递不过来的,所以导致了SlideMenu无法滑动。

 

 

如果我们设置了clickable,那么第一个ACTION_DOWN就被TextView处理了,所以后面每个事件都会传递到TextView(前提是不被拦截,实际结果是被拦截,并被SlideMenu处理,所以SlideMenu滑动了)

 

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