GestureDetector.SimpleOnGestureListener中onScroll的参数e2.getX的问题

ZYLab 2012-02-23 12:01:02

我在做一个图片浏览软件，做那种仿launcher桌面的滑动效果时，当滑动到两张图片各占了屏幕显示的一半的时候，就这样一直维持着的话，这两张图片总会有明显的颤动的bug，而图片的移动都是在GestureDetector.SimpleOnGestureListener中onScroll中根据滑动距离实现的。于是我来来查看GestureDetector.SimpleOnGestureListener中的
onScroll(MotionEvent e1, MotionEvent e2,float distanceX, float distanceY) 。就在我手指一直在屏幕上不移动（或有极小颤动）的动情况下，我发现e2.getX的值变化很大。我把log亮出来给大家看看：
02-22 19:48:46.853: INFO/offset(19060): e1.getX:277.16916
02-22 19:48:46.853: INFO/offset(19060): e2.getX:196.0465
02-22 19:48:46.853: INFO/offset(19060): mCurrentOffset:0.0
02-22 19:48:46.853: INFO/offset(19060): currentScrollDelta:81.122665
02-22 19:48:46.853: INFO/offset(19060): scrollOffset:81
02-22 19:48:46.853: INFO/offset(19060): -----------------------------------
02-22 19:48:46.881: INFO/offset(19060): e1.getX:277.16916
02-22 19:48:46.881: INFO/offset(19060): e2.getX:120.147385
02-22 19:48:46.881: INFO/offset(19060): mCurrentOffset:0.0
02-22 19:48:46.881: INFO/offset(19060): currentScrollDelta:157.02177
02-22 19:48:46.881: INFO/offset(19060): scrollOffset:157
02-22 19:48:46.881: INFO/offset(19060): -----------------------------------
02-22 19:48:46.891: INFO/offset(19060): e1.getX:277.16916
02-22 19:48:46.891: INFO/offset(19060): e2.getX:197.41345
02-22 19:48:46.891: INFO/offset(19060): mCurrentOffset:0.0
02-22 19:48:46.891: INFO/offset(19060): currentScrollDelta:79.75571
02-22 19:48:46.891: INFO/offset(19060): scrollOffset:80
02-22 19:48:46.891: INFO/offset(19060): -----------------
.....

基本上e2.getX就是在120与197之间切换，于是我就搞不明白了，e2.getX为啥总是这样改变呢？我的手指又没怎么动啊？
一些关键代码帖上来：



我是抄别人例子的，代码仓库中一个叫photostore的图片浏览器的例子 onScroll代码如下:

                 public boolean onScroll(MotionEvent e1, MotionEvent e2,

                                 float distanceX, float distanceY) {

                         if (e2.getAction() == MotionEvent.ACTION_MOVE) {

                                 if (mIsDragging == false) {

                                         // Stop animation

                                         mIsTouched = true;



                                         // Reconfigure scroll

                                         mIsDragging = true;

                                         mFlingDirection = 0;

                                         mScrollTimestamp = System.currentTimeMillis();

                                         mCurrentOffset = mViews[mCurrentViewNumber]

                                                         .getCurrentOffset();

                                 }



                                 // mA是恒的是250

                                 float maxVelocity = mGalleryWidth

                                                 / (mAnimationDuration / 1000.0f);

                                 // 连续滑动时间

                                 long timestampDelta = System.currentTimeMillis()

                                                 - mScrollTimestamp;

                                 float maxScrollDelta = maxVelocity * (timestampDelta / 1000.0f);

                                 float currentScrollDelta = e1.getX() - e2.getX();

                                 if (currentScrollDelta < maxScrollDelta * -1)

                                         currentScrollDelta = maxScrollDelta * -1;

                                 if (currentScrollDelta > maxScrollDelta)

                                         currentScrollDelta = maxScrollDelta;

                                 int scrollOffset = Math.round(mCurrentOffset

                                                 + currentScrollDelta);



                                 // We can't scroll more than the width of our own frame layout

                                 if (scrollOffset >= mGalleryWidth)

                                         scrollOffset = mGalleryWidth;

                                 if (scrollOffset <= mGalleryWidth * -1)

                                         scrollOffset = mGalleryWidth * -1;



                                 mViews[0].setOffset(scrollOffset, 0, mCurrentViewNumber);

                                 mViews[1].setOffset(scrollOffset, 0, mCurrentViewNumber);

                                 mViews[2].setOffset(scrollOffset, 0, mCurrentViewNumber);

                         }

                         return false;

                 }



		public void setOffset(int xOffset, int yOffset, int relativeViewNumber) {

			// Scroll the target view relative to its own position relative to

			// currently displayed view

			mInternalLayout.scrollTo(

					getViewOffset(mViewNumber, relativeViewNumber) + xOffset,

					yOffset);

		}

需要说的是，我的onGestureListener是这样调用的：
下边这个onTouch是一个叫ZoomImageView的自定义控件，实现双手触摸改变图片大小



	public boolean onTouch(View v, MotionEvent event) {



		final int action = event.getAction();

		int pointCount = event.getPointerCount();

		if (pointCount == 1) {

                        //fg.就是上边GestureDectector来监听的一个自定义控件叫myGallery吧

			fg.onTouchEvent(event);

			final float y = event.getY();

			switch (action) {

			case MotionEvent.ACTION_DOWN:

				mY = y;

				break;

			case MotionEvent.ACTION_MOVE:

				final float dy = (y - mY) / v.getHeight();

				mState.setPanY(mState.getPanY() - dy);

				mState.notifyObservers();

				mY = y;

				break;

			}

		}

		if (pointCount == 2) {

			final float x0 = event.getX(event.getPointerId(0));

			final float y0 = event.getY(event.getPointerId(0));



			final float x1 = event.getX(event.getPointerId(1));

			final float y1 = event.getY(event.getPointerId(1));



			final float gap = getGap(x0, x1, y0, y1);

			switch (action) {

			case MotionEvent.ACTION_POINTER_2_DOWN:

			case MotionEvent.ACTION_POINTER_1_DOWN:

				mGap = gap;

				break;

			case MotionEvent.ACTION_POINTER_1_UP:

				mX = x1;

				mY = y1;

				break;

			case MotionEvent.ACTION_POINTER_2_UP:

				mX = x0;

				mY = y0;

				break;

			case MotionEvent.ACTION_MOVE: {

				final float dgap = (gap - mGap) / mGap;

				// Log.d("Gap", String.valueOf(dgap));

				Log.d("Gap", String.valueOf((float) Math.pow(20, dgap)));

				mState.setZoom(mState.getZoom() * (float) Math.pow(5, dgap));

				mState.notifyObservers();

				mGap = gap;

				break;

			}

			}

		}

		return true;

	}

我所仿的demo 并不是在myGallery中放入zoomImageView进行滑动而是放入ImageView的,就没e2.getX 大幅改变的问题~因为ZoomImageView 是先获得touch的，只有在单点触摸时才会让其响应myGallery的onGestureListener ,我怀疑可能是这里的问题，但我还是找不到～～
谢啦～

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