转载

Make your OverScrollLayout

posted @ by avenwu

前言

手势处理在自定义控件中随处可见，诸如下拉，侧滑，加载更多等等，本文将利用手势相关的知识，来实现一个类似微信文章中过渡滑动交互。

下滑的处理在很早之前也写过几篇分别是简单的下拉，侧滑，原理基本类似，主要依赖的是offsetTopBotom,offsetLeftRight,Scroller；

在处理OverScroll的时候需要正确决定手势是否被拦截用于，滑动视图，或者分发至系统时间响应，根据内容区视图是否能滑动也有细节上的处理，这一块可以参照SwpieRefreshLayout的处理，即提供一个检测方法canChildScroolUp，针对内容view的类型单独处理;

下面是最终实现的效果：

控件定义

首先考虑一下，这个效果的UI组成，当滑动到顶部时可以继续滑动，展示底部的视图；因此滑动主要解决的是视图在Y轴上的偏移：

Make your OverScrollLayout

区分内容视图和背景视图允许视图内包含一个背景View和一个内容View，为便于理解，参照FrameLayout，xml内第一个的view作为底视图，第二个作为内容视图对子View的关系约定，可以放在合适的地方，比如inflate，或者第一次measure，layout时

if (count > 1) {     mForegroundView = getChildAt(1);     mBackgroundView = getChildAt(0); } else {     mForegroundView = getChildAt(0); }

视图排版初始化视图，后需要根据规范对View的measure，layout响应处理

    @Override     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {         super.onMeasure(widthMeasureSpec, heightMeasureSpec);         int count = getChildCount();         log("onMeasure: count=" + count);         if (count > 1) {             mForegroundView = getChildAt(1);             mBackgroundView = getChildAt(0);         } else {             mForegroundView = getChildAt(0);         }         if (mBackgroundView != null) {             measureChildWithMargins(mBackgroundView, widthMeasureSpec, 0, heightMeasureSpec, 0);         }         if (mForegroundView != null) {             measureChildWithMargins(mForegroundView, widthMeasureSpec, 0, heightMeasureSpec, 0);             mHeightLimitMax = (int) (mForegroundView.getMeasuredHeight() * mMaxOverPercent);             if (mForegroundView instanceof ScrollIntercept) {                 ((ScrollIntercept) mForegroundView).attach(this);             }         }         if (mForegroundView != null && mBackgroundView != null) {             mForegroundView.bringToFront();         }     }      @Override     protected void onLayout(boolean changed, int l, int t, int r, int b) {         if (mBackgroundView != null) {             MarginLayoutParams layoutParams = (MarginLayoutParams) mBackgroundView.getLayoutParams();             int left = layoutParams.leftMargin + getPaddingLeft();             int top = layoutParams.topMargin + getPaddingTop();             int right = left + mBackgroundView.getMeasuredWidth();             int bottom = top + mBackgroundView.getMeasuredHeight();             mBackgroundView.layout(left, top, right, bottom);             log("onLayout, mBackgroudView = " + mBackgroundView.toString() +                     ", l=" + left + ",t=" + top + ", r=" + right + ",b=" + bottom);         }         if (mForegroundView != null) {             MarginLayoutParams layoutParams = (MarginLayoutParams) mForegroundView.getLayoutParams();             int left = layoutParams.leftMargin + getPaddingLeft();             int top = layoutParams.topMargin + getPaddingTop();             int right = left + mForegroundView.getMeasuredWidth();             int bottom = top + mForegroundView.getMeasuredHeight();             mForegroundView.layout(left, top, right, bottom);             log("onLayout, mForegroundView = " + mForegroundView.toString() +                     ", l=" + left + ",t=" + top + ", r=" + right + ",b=" + bottom);         }     }

重载onInterceptTouchEvent 当手势在滑动且是上下滑动，超过touchslop时，开始拦截；

    @Override     public boolean onInterceptTouchEvent(MotionEvent ev) {         log("onInterceptTouchEvent:" + ev.toString());         if (!isEnabled() || canChildScrollUp()) {             //make child layout to determine the scroll state             if (mForegroundView instanceof ScrollIntercept &&                     (ev.getAction() == MotionEvent.ACTION_CANCEL || ev.getAction() == MotionEvent.ACTION_UP)) {                 log("try tryScrollToTop");                 ((ScrollIntercept) mForegroundView).tryScrollToTop(this);             }             return false;         }         final int action = ev.getAction();         if (action != MotionEvent.ACTION_DOWN && isSliding) return true;         switch (action) {             case MotionEvent.ACTION_DOWN:                 isSliding = false;                 mX = ev.getX();                 mY = ev.getY();                 break;             case MotionEvent.ACTION_CANCEL:             case MotionEvent.ACTION_UP:                 isSliding = false;                 break;             case MotionEvent.ACTION_MOVE:                 float dy = ev.getY() - mY;                 log("onInterceptTouchEvent, canChildScrollUp=" + canChildScrollUp());                 if (dy > mTouchSlop && !isSliding) {                     mY = ev.getY();                     mX = ev.getX();                     isSliding = true;                     log("dy=" + dy);                 }                 break;          }         log("onInterceptTouchEvent, isSliding=" + isSliding);         return isSliding;     }

重载onTouch 这里可以开始根据move的具体值，调整view的offset

    @Override     public boolean onTouchEvent(MotionEvent event) {         log("onTouchEvent:" + event.toString());         if (!isEnabled() || canChildScrollUp()) {             // Fail fast if we're not in a state where a swipe is possible             return false;         }         switch (event.getAction()) {             case MotionEvent.ACTION_DOWN:                 mX = event.getX();                 mY = event.getY();                 isSliding = false;                 if (!mScroller.isFinished()) {                     mScroller.abortAnimation();                 }             case MotionEvent.ACTION_MOVE:                 float offsetX = event.getX() - mX;                 float offsetY = event.getY() - mY;                 log("move, offsetX=" + offsetX + ", offsetY=" + offsetY + ", mTouchSlop=" + mTouchSlop);                 if (isSliding) {                     if (offsetY > 0) {                         scrollY((int) offsetY);                         mX = event.getX();                         mY = event.getY();                     } else {                         return false;                     }                 }                 break;             case MotionEvent.ACTION_CANCEL:             case MotionEvent.ACTION_UP:                 if (!mScroller.isFinished()) {                     mScroller.abortAnimation();                 }                 int currentY = mForegroundView.getTop();                 int gap = (int) (mForegroundView.getHeight() * mOverPercent);                 if (currentY + event.getY() - mY >= gap / 2) {                     int duration = (int) (Math.abs(0 - currentY + 0.5f) / mForegroundView.getHeight() * 1000);                     log("duration=" + duration);                     mScroller.startScroll(0, currentY, 0, 0 - currentY, duration);                 } else {                     int duration = (int) (Math.abs(-gap - currentY + 0.5f) / mForegroundView.getHeight() * 1000);                     log("duration=" + duration);                     mScroller.startScroll(0, currentY, 0, -gap - currentY, duration);                 }                 isSliding = false;                 invalidate();                 return false;         }         return true;     }

支持WebView 需要注意的是WebView在JellyBean之后内部实现有了很大变化，参考其源码实现可以证实，大量的具体逻辑都已经委托个了一个Provider实现类，这直接导致webview无法和其他view一样检测出其滑动位置；因此为了兼容WebView，需要在WebView内的OverScroll回调内手动再次处理offset，这一点实际上时参考了ChrisBean的Pull2Refresh的实现；

    @Override     public void tryScrollToTop(ScrollOver layout) {         log("tryScrollToTop:" + mScrolledY);         if (mScrolledY != 0) {             mLayout.smooth2Top();             mScrolledY = 0;         }     }      @Override     protected boolean overScrollBy(int deltaX, int deltaY, int scrollX, int scrollY, int scrollRangeX, int scrollRangeY, int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent) {         log("overScrollBy: deltaX=" + deltaX + ", deltaY=" + deltaY + ", scrollX=" + scrollX + ", scrollRangeX=" + scrollRangeX);         final boolean returnValue = super.overScrollBy(deltaX, deltaY, scrollX, scrollY, scrollRangeX,                 scrollRangeY, maxOverScrollX, maxOverScrollY, isTouchEvent);          if (mLayout != null) {             mScrolledY += deltaY;             mLayout.scrollY(-deltaY);         }         return returnValue;     }