先看看效果图:

 

因为没有具体内容,也没有简书的图片资源,所以稍微简陋了点.
但是依然不妨碍我们的效果展示~

OK,接下来惯例,通过阅读本文你能学习到:

  1. ViewDragHelper的使用(如果你想学习自定义View,那么ViewDragHelper你绝对不能错过)
  2. 好像也没有什么了….

这个效果,难度不大,会ViewDragHelper的同学应该10分钟就能写出来了吧~
如果不会也没关系~

1. 我们自定义一个SwipeBackFrameLayout继承自FrameLayout

1.1 因为看到左边黄色的View是被遮住的,而另外一个View的宽度是MatchParent的,所以FrameLayout是不错的选择.
顺便增加一个回调,通知activity去finish

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public void setCallback(Callback mCallback){
     this.mCallback = mCallback;
}
private Callback mCallback;
public interface Callback{
     void onShouldFinish();
}
 

1.2 Xml布局,非常简单:

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<yifeiyuan.practice.practicedemos.drager.SwipeBackFrameLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools"
     android:id="@+id/swipe_back"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     tools:context="yifeiyuan.practice.practicedemos.drager.SwipeBackActivity">
     <TextView
           android:layout_width="40dp"
           android:layout_height="match_parent"
           android:text="@string/hello_world"
           android:gravity="center"
           android:background="#ffff00" />
     <View
           android:layout_width="match_parent"
           android:layout_height="match_parent"
           android:background="#ff00ff" />
</yifeiyuan.practice.practicedemos.drager.SwipeBackFrameLayout>
 

1.3 实例化一个ViewDragHelper

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//1f代表灵敏度
mDragHelper = ViewDragHelper.create(this, 1f,new ViewDragHelper.Callback() {
     @Override
     public boolean tryCaptureView(View child, int pointerId) {
          return false;
     }
}
//因为我们是从左向右滑动 所以设置EDGE_LEFT
mDragHelper.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT);
 

1.4 在SwipeBackFrameLayout里实例化xml里的子View

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private View mDividerView;
private View mContentView;
@Override
protected void onFinishInflate() {
     super.onFinishInflate();
     mDividerView = getChildAt(0);
     mDividerView.setAlpha(0f);
     mContentView = getChildAt(1);
}
 

1.5 让ViewDragHelper处理touch事件

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@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
     return mDragHelper.shouldInterceptTouchEvent(ev);
}
 
@Override
public boolean onTouchEvent(MotionEvent event) {
     mDragHelper.processTouchEvent(event);
     return true;
}
 

1.6重写ViewDragHelper的一些处理方法

已附上详细注释

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@Override
public void onEdgeTouched(int edgeFlags, int pointerId) {
     super.onEdgeTouched(edgeFlags, pointerId);
     //触摸到左边界的时候 我们capture住mContentView
     mDragHelper.captureChildView(mContentView, pointerId);
}
@Override
public int getViewHorizontalDragRange(View child) {
     return 1;
}
 
@Override
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
     super.onViewPositionChanged(changedView, left, top, dx, dy);
     Log.d(TAG, "onViewPositionChanged() called with left = [" + left + "], top = [" + top + "], dx = [" + dx + "], dy = [" + dy + "]");
     //0.0 - 1.0
     //Notice 这边可以给个接口回调出去,就可以做各种炫酷的效果了
     float alpha = (float) (left*1.0/mDividerWidth);
     mDividerView.setAlpha(alpha);
}
 
@Override
public int clampViewPositionHorizontal(View child, int left, int dx) {
     // Log.d(TAG, "clampViewPositionHorizontal() called with dx = [" + dx + "]");
     // 计算left 我们的目标范围是0-dividerwidth的宽度
     mLastdx = dx;
     int newLeft = Math.min(mDividerWidth, Math.max(left,0));
     return newLeft;
}
@Override
public void onViewReleased(View releasedChild, float xvel, float yvel) {
     //>0代表用户想关闭
     if (mLastdx>0){
         // 还不到关闭条件,我们让view滑动过去,再关闭
         if (mDividerWidth != releasedChild.getLeft()) {
              mDragHelper.settleCapturedViewAt(mDividerWidth,releasedChild.getTop();
              invalidate();
         } else {
              if (mCallback != null) {
                    mCallback.onShouldFinish();
              }
         }
     }else{
         //用户不想关闭 ,则滑动到最左边
         if (mDividerWidth != 0) {
             mDragHelper.settleCapturedViewAt(0, releasedChild.getTop());
             invalidate();
         }
     }
}
 
@Override
public void onViewDragStateChanged(int state) {
     super.onViewDragStateChanged(state);
     //滑动停止,并且到达了滑动的判断条件 则回调关闭
     if(mDragHelper.getViewDragState()==ViewDragHelper.STATE_IDLE&&mCallback != null&&mDividerWidth==mContentView.getLeft()&&mLastdx>0) {
          mCallback.onShouldFinish();
     }
}
});
 

1.7 增加对view滑动事件处理,对于以上mDividerWidth我们在onLayout里获取

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private int mDividerWidth;
 
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
      super.onLayout(changed, left, top, right, bottom);
      mDividerWidth = mDividerView.getWidth();
}
//Notice view 刚初始化的时候就会被调用一次
@Override
public void computeScroll() {
     super.computeScroll();
     // Log.d(TAG, "computeScroll() called with " + "");
     if (mDragHelper.continueSettling(true)) {
          invalidate();
     }
}
 

我们写完自定义view后还需要自定义一下activity的退出动画~

2.定义activity的finish动画

2.1 在anim目录下,创建两个动画xml:

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//no_anim
<alpha
     android:duration="300"
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:fromAlpha="1.0"
     android:toAlpha="1.0" >
</alpha>
 
//out_to_right
<translate
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:duration="300"
     android:fromXDelta="0%"
     android:toXDelta="100%" >
</translate>
 

2.2 在activity里设置callback监听,并运用动画

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mSwipeBack.setCallback(new SwipeBackFrameLayout.Callback() {
      @Override
      public void onShouldFinish() {
            finish();
            overridePendingTransition(R.anim.no_anim, R.anim.out_to_right);
      }
});
 

好了!!~代码量非常少!~就是这么简单~

吐槽一下,简书对代码块的支持太差了,代码复制过来全是乱的!!

同学们还是去看源码吧:

源码在我的Github上

原文：http://www.jianshu.com/p/59be4551c418