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剖析Android|剖析Android Activity侧滑返回的实现原理

简介 使用侧滑Activity返回很常见，例如微信就用到了。那么它是怎么实现的呢。本文带你剖析一下实现原理。我在github上找了一个star有2.6k的开源，我们分析他是怎么实现的

//star 2.6k'com.r0adkll:slidableactivity:2.0.5'

Slidr使用示例 它的使用很简单，首先要设置透明的窗口背景
falsefalsefalsetrue@color/colorPrimary@color/colorPrimaryDark@color/colorAccenttrue@android:color/transparent

【剖析Android|剖析Android Activity侧滑返回的实现原理】然后
//setContent(View view)后Slidr.attach(this);


下面可以从三个步骤看其原理 步骤一 重新包裹界面
Slidr.class
public static SlidrInterface attach(final Activity activity, final int statusBarColor1, final int statusBarColor2){//0创建滑动嵌套界面SliderPanelfinal SliderPanel panel = initSliderPanel(activity, null); //7 Set the panel slide listener for when it becomes closed or opened// 监听回调panel.setOnPanelSlideListener(new SliderPanel.OnPanelSlideListener() {...//open close等}); // Return the lock interfacereturn initInterface(panel); } private static SliderPanel initSliderPanel(final Activity activity, final SlidrConfig config) {//3 获取decorviewViewGroup decorView = (ViewGroup)activity.getWindow().getDecorView(); //4 获取我们布局的内容并删除View oldScreen = decorView.getChildAt(0); decorView.removeViewAt(0); //5 Setup the slider panel and attach it to the decor// 建立滑动嵌套视图SliderPanel并且添加到DecorView中SliderPanel panel = new SliderPanel(activity, oldScreen, config); panel.setId(R.id.slidable_panel); oldScreen.setId(R.id.slidable_content); //6 把我们的界面布局添加到SliderPanel，并且把SliderPanel添加到decorView中panel.addView(oldScreen); decorView.addView(panel, 0); return panel; }

步骤二 使用ViewDragHelper.class处理滑动手势
SliderPanel.class
private void init(){...//1 ViewDragHelper创建mDragHelper = ViewDragHelper.create(this, mConfig.getSensitivity(), callback); mDragHelper.setMinVelocity(minVel); mDragHelper.setEdgeTrackingEnabled(mEdgePosition); //2 Setup the dimmer view 添加用于指示滑动过程的View到底层mDimView = new View(getContext()); mDimView.setBackgroundColor(mConfig.getScrimColor()); mDimView.setAlpha(mConfig.getScrimStartAlpha()); addView(mDimView); }

步骤三 在ViewDragHelper.Callback中处理我们的界面的拖动
我们首先明确ViewDragHelper仅仅是处理ParentView与它子View的关系，不会一直遍历到最顶层的View。ViewDragHelper的捕获capture是这样实现的
@Nullablepublic View findTopChildUnder(int x, int y) {final int childCount = mParentView.getChildCount(); for (int i = childCount - 1; i >= 0; i--) {final View child = mParentView.getChildAt(mCallback.getOrderedChildIndex(i)); if (x >= child.getLeft() && x < child.getRight()&& y >= child.getTop() && y < child.getBottom()) {return child; }}return null; }

重点在SliderPanel.class的ViewDragHelper.Callback callback的实现，作者实现实现了很多个方向的滑动处理mLeftCallback、mRightCallback、mTopCallback、mBottomCallback、mVerticalCallback、mHorizontalCallback, 我们取mLeftCallback来分析
private ViewDragHelper.Callback mLeftCallback = new ViewDragHelper.Callback() {//捕获View@Overridepublic boolean tryCaptureView(View child, int pointerId) {boolean edgeCase = !mConfig.isEdgeOnly() || mDragHelper.isEdgeTouched(mEdgePosition, pointerId); //像前面说的，我们的内容是最上层子View，mDecorView这里指的是我们的contentViewreturn child.getId() == mDecorView.getId() && edgeCase; }//拖动， 最终是通过view.offsetLeftAndRight(offset)实现移动@Overridepublic int clampViewPositionHorizontal(View child, int left, int dx) {return clamp(left, 0, mScreenWidth); }//滑动范围@Overridepublic int getViewHorizontalDragRange(View child) {return mScreenWidth; }//释放处理，判断是滚回屏幕@Overridepublic void onViewReleased(View releasedChild, float xvel, float yvel) {super.onViewReleased(releasedChild, xvel, yvel); int left = releasedChild.getLeft(); int settleLeft = 0; int leftThreshold = (int) (getWidth() * mConfig.getDistanceThreshold()); boolean isVerticalSwiping = Math.abs(yvel) > mConfig.getVelocityThreshold(); if(xvel > 0){if(Math.abs(xvel) > mConfig.getVelocityThreshold() && !isVerticalSwiping){settleLeft = mScreenWidth; }else if(left > leftThreshold){settleLeft = mScreenWidth; }}else if(xvel == 0){if(left > leftThreshold){settleLeft = mScreenWidth; }}//滚动到left=0(正常布局) 或者 滚动到left=mScreenWidth（滚出屏幕）关闭ActivitymDragHelper.settleCapturedViewAt(settleLeft, releasedChild.getTop()); invalidate(); }//转换位置百分比，确定指示层的透明度@Overridepublic void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {super.onViewPositionChanged(changedView, left, top, dx, dy); float percent = 1f - ((float)left / (float)mScreenWidth); if(mListener != null) mListener.onSlideChange(percent); // Update the dimmer alphaapplyScrim(percent); }//回调到Slidr处理Activity状态@Overridepublic void onViewDragStateChanged(int state) {super.onViewDragStateChanged(state); if(mListener != null) mListener.onStateChanged(state); switch (state){case ViewDragHelper.STATE_IDLE:if(mDecorView.getLeft() == 0){// State Openif(mListener != null) mListener.onOpened(); }else{// State Closed这里回调到Slidr处理activity.finish()if(mListener != null) mListener.onClosed(); }break; case ViewDragHelper.STATE_DRAGGING:break; case ViewDragHelper.STATE_SETTLING:break; }}};

对于mDragHelper.settleCapturedViewAt(settleLeft, releasedChild.getTop()); 内部是使用Scroller.class辅助滚动，所以要在SliderPanel中重写View.computeScroll()
@Overridepublic void computeScroll() {super.computeScroll(); if(mDragHelper.continueSettling(true)){ViewCompat.postInvalidateOnAnimation(this); }}

总结 整体方案如下图所示
剖析Android|剖析Android Activity侧滑返回的实现原理
文章图片

总体来看原理并不复杂, 就是通过ViewDragHelper对View进行拖动。
以上就是Android Activity侧滑返回的实现原理的详细内容，更多关于Activity侧滑返回的资料请关注脚本之家其它相关文章！

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