package com.zhy.learn.view;

import android.content.Context;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.LinearLayout;

/**
 * Created by zhy on 15/6/3.
 */
public class VDHLayout extends LinearLayout
{
 private ViewDragHelper mDragger;

 public VDHLayout(Context context, AttributeSet attrs)
 {
  super(context, attrs);
  mDragger = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback()
  {
   @Override
   public boolean tryCaptureView(View child, int pointerId)
   {
    return true;
   }

   @Override
   public int clampViewPositionHorizontal(View child, int left, int dx)
   {
    return left;
   }

   @Override
   public int clampViewPositionVertical(View child, int top, int dy)
   {
    return top;
   }
  });
 }

 @Override
 public boolean onInterceptTouchEvent(MotionEvent event)
 {
  return mDragger.shouldInterceptTouchEvent(event);
 }

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

mDragger = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback()
  {
  });

helper.mTouchSlop = (int) (helper.mTouchSlop * (1 / sensitivity));

 @Override
 public boolean onInterceptTouchEvent(MotionEvent event)
 {
  return mDragger.shouldInterceptTouchEvent(event);
 }

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

new ViewDragHelper.Callback()
  {
   @Override
   public boolean tryCaptureView(View child, int pointerId)
   {
    return true;
   }

   @Override
   public int clampViewPositionHorizontal(View child, int left, int dx)
   {
    return left;
   }

   @Override
   public int clampViewPositionVertical(View child, int top, int dy)
   {
    return top;
   }
  }

 @Override
   public int clampViewPositionHorizontal(View child, int left, int dx)
   {
    final int leftBound = getPaddingLeft();
    final int rightBound = getWidth() - mDragView.getWidth() - leftBound;

    final int newLeft = Math.min(Math.max(left, leftBound), rightBound);

    return newLeft;
   }

<com.zhy.learn.view.VDHLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:orientation="vertical"
        android:layout_height="match_parent"
 >

 <TextView
  android:layout_margin="10dp"
  android:gravity="center"
  android:layout_gravity="center"
  android:background="#44ff0000"
  android:text="I can be dragged !"
  android:layout_width="100dp"
  android:layout_height="100dp"/>

 <TextView
  android:layout_margin="10dp"
  android:layout_gravity="center"
  android:gravity="center"
  android:background="#44ff0000"
  android:text="I can be dragged !"
  android:layout_width="100dp"
  android:layout_height="100dp"/>

 <TextView
  android:layout_margin="10dp"
  android:layout_gravity="center"
  android:gravity="center"
  android:background="#44ff0000"
  android:text="I can be dragged !"
  android:layout_width="100dp"
  android:layout_height="100dp"/>

</com.zhy.learn.view.VDHLayout>

package com.zhy.learn.view;

import android.content.Context;
import android.graphics.Point;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.LinearLayout;

/**
 * Created by zhy on 15/6/3.
 */
public class VDHLayout extends LinearLayout
{
 private ViewDragHelper mDragger;

 private View mDragView;
 private View mAutoBackView;
 private View mEdgeTrackerView;

 private Point mAutoBackOriginPos = new Point();

 public VDHLayout(Context context, AttributeSet attrs)
 {
  super(context, attrs);
  mDragger = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback()
  {
   @Override
   public boolean tryCaptureView(View child, int pointerId)
   {
    //mEdgeTrackerView禁止直接移动
    return child == mDragView || child == mAutoBackView;
   }

   @Override
   public int clampViewPositionHorizontal(View child, int left, int dx)
   {
    return left;
   }

   @Override
   public int clampViewPositionVertical(View child, int top, int dy)
   {
    return top;
   }


   //手指释放的时候回调
   @Override
   public void onViewReleased(View releasedChild, float xvel, float yvel)
   {
    //mAutoBackView手指释放时可以自动回去
    if (releasedChild == mAutoBackView)
    {
     mDragger.settleCapturedViewAt(mAutoBackOriginPos.x, mAutoBackOriginPos.y);
     invalidate();
    }
   }

   //在边界拖动时回调
   @Override
   public void onEdgeDragStarted(int edgeFlags, int pointerId)
   {
    mDragger.captureChildView(mEdgeTrackerView, pointerId);
   }
  });
  mDragger.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT);
 }


 @Override
 public boolean onInterceptTouchEvent(MotionEvent event)
 {
  return mDragger.shouldInterceptTouchEvent(event);
 }

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

 @Override
 public void computeScroll()
 {
  if(mDragger.continueSettling(true))
  {
   invalidate();
  }
 }

 @Override
 protected void onLayout(boolean changed, int l, int t, int r, int b)
 {
  super.onLayout(changed, l, t, r, b);

  mAutoBackOriginPos.x = mAutoBackView.getLeft();
  mAutoBackOriginPos.y = mAutoBackView.getTop();
 }

 @Override
 protected void onFinishInflate()
 {
  super.onFinishInflate();

  mDragView = getChildAt(0);
  mAutoBackView = getChildAt(1);
  mEdgeTrackerView = getChildAt(2);
 }
}

@Override
public int getViewHorizontalDragRange(View child)
{
  return getMeasuredWidth()-child.getMeasuredWidth();
}

@Override
public int getViewVerticalDragRange(View child)
{
  return getMeasuredHeight()-child.getMeasuredHeight();
}

shouldInterceptTouchEvent：

DOWN:
  getOrderedChildIndex(findTopChildUnder)
  ->onEdgeTouched

MOVE:
  getOrderedChildIndex(findTopChildUnder)
  ->getViewHorizontalDragRange & 
   getViewVerticalDragRange(checkTouchSlop)(MOVE中可能不止一次)
  ->clampViewPositionHorizontal&
   clampViewPositionVertical
  ->onEdgeDragStarted
  ->tryCaptureView
  ->onViewCaptured
  ->onViewDragStateChanged

processTouchEvent:

DOWN:
  getOrderedChildIndex(findTopChildUnder)
  ->tryCaptureView
  ->onViewCaptured
  ->onViewDragStateChanged
  ->onEdgeTouched
MOVE:
  ->STATE==DRAGGING:dragTo
  ->STATE!=DRAGGING:
    onEdgeDragStarted
    ->getOrderedChildIndex(findTopChildUnder)
    ->getViewHorizontalDragRange&
     getViewVerticalDragRange(checkTouchSlop)
    ->tryCaptureView
    ->onViewCaptured
    ->onViewDragStateChanged