Android开发之使用150行代码实现滑动返回效果

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

//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);

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

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

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

@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(); 
    }
   }
  });

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();
  }
}

//no_anim


//out_to_right

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