Android ViewDragHelper使用介绍

public DrawerLayout(Context context, AttributeSet attrs, int defStyle) { 
  super(context, attrs, defStyle); 
  setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS); 
  final float density = getResources().getDisplayMetrics().density; 
  mMinDrawerMargin = (int) (MIN_DRAWER_MARGIN * density + 0.5f); 
  final float minVel = MIN_FLING_VELOCITY * density; 
  mLeftCallback = new ViewDragCallback(Gravity.LEFT); 
  mRightCallback = new ViewDragCallback(Gravity.RIGHT); 
  mLeftDragger = ViewDragHelper.create(this, TOUCH_SLOP_SENSITIVITY, mLeftCallback); 
  mLeftDragger.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT); 
  mLeftDragger.setMinVelocity(minVel); 
  mLeftCallback.setDragger(mLeftDragger); 
 
  mRightDragger = ViewDragHelper.create(this, TOUCH_SLOP_SENSITIVITY, mRightCallback); 
  mRightDragger.setEdgeTrackingEnabled(ViewDragHelper.EDGE_RIGHT); 
  mRightDragger.setMinVelocity(minVel); 
  mRightCallback.setDragger(mRightDragger); 
 
  //省略 
 } 

/** 
 * Factory method to create a new ViewDragHelper. 
 * 
 * @param forParent Parent view to monitor 
 * @param cb Callback to provide information and receive events 
 * @return a new ViewDragHelper instance 
 */ 
 public static ViewDragHelper create(ViewGroup forParent, Callback cb) { 
  return new ViewDragHelper(forParent.getContext(), forParent, cb); 
 } 

@Override 
public boolean onInterceptTouchEvent(MotionEvent ev) { 
 //由ViewDragHelper类来决定是否要拦截事件 
 return dragHelper.shouldInterceptTouchEvent(ev); 
} 
@Override 
public boolean onTouchEvent(MotionEvent event) { 
 try { 
  //由ViewDragHelper类来决定是否要处理触摸事件,这里可能有异常 
  dragHelper.processTouchEvent(event); 
 } catch (Exception e) { 
  e.printStackTrace(); 
 } 
 //返回true,可以持续接收到后续事件 
 return true; 
} 

/** 
 * Created by mChenys on 2015/12/16. 
 */ 
public class DragLayout extends FrameLayout { 
 private String TAG = "DragLayout"; 
 private ViewDragHelper dragHelper; 
 private LinearLayout mLeftContent; //左侧面板 
 private LinearLayout mMainContent;//主体面板 
 
 public DragLayout(Context context) { 
  this(context, null); 
 } 
 
 public DragLayout(Context context, AttributeSet attrs) { 
  this(context, attrs, 0); 
 } 
 
 public DragLayout(Context context, AttributeSet attrs, int defStyleAttr) { 
  super(context, attrs, defStyleAttr); 
  init(); 
 } 
 //重写此方法,可以获取该容器下的所有的直接子View 
 @Override 
 protected void onFinishInflate() { 
  super.onFinishInflate(); 
  mLeftContent = (LinearLayout) getChildAt(0); 
  mMainContent = (LinearLayout) getChildAt(1); 
 } 
  
 private void init() { 
  //step1 通过ViewDragHelper的单例方法获取ViewDragHelper的实例 
  dragHelper = ViewDragHelper.create(this, mCallback); 
 } 
 //step2 传递触摸事件,需要重写onInterceptTouchEvent和onTouchEvent 
 @Override 
 public boolean onInterceptTouchEvent(MotionEvent ev) { 
  //由ViewDragHelper类来决定是否要拦截事件 
  return dragHelper.shouldInterceptTouchEvent(ev); 
 } 
 @Override 
 public boolean onTouchEvent(MotionEvent event) { 
  try { 
   //由ViewDragHelper类来决定是否要处理触摸事件 
   dragHelper.processTouchEvent(event); 
  } catch (Exception e) { 
   e.printStackTrace(); 
  } 
  //返回true,可以持续接收到后续事件 
  return true; 
 } 
 //step3 重写ViewDragHelper.Callback()的相关回调方法,处理事件 
 private ViewDragHelper.Callback mCallback = new ViewDragHelper.Callback() { 
  /** 
   * 1.改方法是abstract的方法,必须要实现,其返回结果决定当前child是否可以拖拽 
   * @param child 当前被拖拽的view 
   * @param pointerId pointerId 区分多点触摸的id 
   * @return true表示允许拖拽, false则不允许拖拽 ,默认返回false 
   */ 
  @Override 
  public boolean tryCaptureView(View child, int pointerId) { 
   Log.d(TAG, "tryCaptureView:当前被拖拽的view:" + child); 
   return false; 
  } 
 }; 
} 

<?xml version="1.0" encoding="utf-8"?> 
<mchenys.net.csdn.blog.mytencentqq.view.DragLayout xmlns:android="http://schemas.android.com/apk/res/android" 
 android:id="@+id/dragLayout" 
 android:layout_width="match_parent" 
 android:layout_height="match_parent"> 
 <!--左侧--> 
 <LinearLayout 
  android:id="@+id/layout_left" 
  android:layout_width="match_parent" 
  android:layout_height="match_parent" 
  android:background="@android:color/holo_red_light" 
  android:orientation="vertical"> 
  <TextView 
   android:layout_width="match_parent" 
   android:layout_height="match_parent" 
   android:gravity="center" 
   android:text="左侧" 
   android:textSize="30sp" /> 
 </LinearLayout> 
 <!--主体布局--> 
 <LinearLayout 
  android:id="@+id/layout_main" 
  android:layout_width="match_parent" 
  android:layout_height="match_parent" 
  android:background="@android:color/holo_blue_light" 
  android:orientation="vertical"> 
  <TextView 
   android:layout_width="match_parent" 
   android:layout_height="match_parent" 
   android:gravity="center" 
   android:text="主体" 
   android:textSize="30sp" /> 
 </LinearLayout> 
</mchenys.net.csdn.blog.mytencentqq.view.DragLayout> 

D/DragLayout: tryCaptureView:当前被拖拽的view:android.widget.LinearLayout{32f4d44b V.E..... ........ 0,0-720,1134 #7f0c0052 app:id/layout_main} 
D/DragLayout: tryCaptureView:当前被拖拽的view:android.widget.LinearLayout{32f4d44b V.E..... ........ 0,0-720,1134 #7f0c0052 app:id/layout_main} 
D/DragLayout: tryCaptureView:当前被拖拽的view:android.widget.LinearLayout{32f4d44b V.E..... ........ 0,0-720,1134 #7f0c0052 app:id/layout_main} 
D/DragLayout: tryCaptureView:当前被拖拽的view:android.widget.LinearLayout{32f4d44b V.E..... ........ 0,0-720,1134 #7f0c0052 app:id/layout_main} 

@Override 
public boolean tryCaptureView(View child, int pointerId) { 
 Log.d(TAG, "tryCaptureView:当前被拖拽的view:" + child); 
 if (child == mMainContent) { 
  return true; //只有主题布局可以被拖动 
 } 
 return false; 
} 

/** 
 * 根据建议值修正将要移动到的横向位置,此时没有发生真正的移动 
 * @param child 当前被拖拽的View 
 * @param left 新的建议值 
 * @param dx 水平位置的变化量 
 * @return 
 */ 
@Override 
public int clampViewPositionHorizontal(View child, int left, int dx) { 
 Log.d(TAG, "clampViewPositionHorizontal:" + "旧的left坐标oldLeft:" + child.getLeft() 
   + " 水平位置的变化量dx:" + dx + " 新的建议值left:" + left); 
  
 return super.clampViewPositionHorizontal(child, left, dx); //父类默认返回0 
} 

tryCaptureView:当前被拖拽的view:android.widget.LinearLayout{23a3c537 V.E..... ........ 0,0-720,1134 #7f0c0052 app:id/layout_main} 
clampViewPositionHorizontal:旧的left坐标oldLeft:0 水平位置的变化量dx:1 新的建议值left:1 
clampViewPositionHorizontal:旧的left坐标oldLeft:0 水平位置的变化量dx:12 新的建议值left:12 
clampViewPositionHorizontal:旧的left坐标oldLeft:0 水平位置的变化量dx:63 新的建议值left:63 
clampViewPositionHorizontal:旧的left坐标oldLeft:0 水平位置的变化量dx:53 新的建议值left:53 
tryCaptureView:当前被拖拽的view:android.widget.LinearLayout{23a3c537 V.E..... ........ 0,0-720,1134 #7f0c0052 app:id/layout_main} 
clampViewPositionHorizontal:旧的left坐标oldLeft:0 水平位置的变化量dx:-5 新的建议值left:-5 
clampViewPositionHorizontal:旧的left坐标oldLeft:0 水平位置的变化量dx:-2 新的建议值left:-2 
clampViewPositionHorizontal:旧的left坐标oldLeft:0 水平位置的变化量dx:-6 新的建议值left:-6 
clampViewPositionHorizontal:旧的left坐标oldLeft:0 水平位置的变化量dx:-11 新的建议值left:-11 

/** 
 * 根据建议值修正将要移动到的纵向位置,此时没有发生真正的移动 
 * @param child 当前被拖拽的View 
 * @param top 新的建议值 
 * @param dy 垂直位置的变化量 
 * @return 
 */ 
@Override 
public int clampViewPositionVertical(View child, int top, int dy) { 
 Log.d(TAG, "clampViewPositionHorizontal:" + "旧的top坐标oldTop:" + child.getTop() 
   + " 垂直位置的变化量dy:" + dy + " 新的建议值top:" + top); 
 return top; 
} 

/** 
 * 当capturedChild被捕获时调用 
 * @param capturedChild 当前被拖拽的view 
 * @param activePointerId 
 */ 
@Override 
public void onViewCaptured(View capturedChild, int activePointerId) { 
 Log.d(TAG, "onViewCaptured:当前被拖拽的view:" + capturedChild); 
 super.onViewCaptured(capturedChild, activePointerId); 
} 

/** 
 * 返回拖拽的范围,不对拖拽进行真正的限制,仅仅决定了动画执行的速度 
 * @param child 
 * @return 返回一个固定值 
 */ 
@Override 
public int getViewHorizontalDragRange(View child) { 
 int range = super.getViewHorizontalDragRange(child); 
 Log.d(TAG, "被拖拽的范围getViewHorizontalDragRange:" + range); 
 return range; 
} 

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

@Override 
protected void onSizeChanged(int w, int h, int oldw, int oldh) { 
 super.onSizeChanged(w, h, oldw, oldh); 
 // 当尺寸有变化的时候调用 
 mHeight = getMeasuredHeight(); 
 mWidth = getMeasuredWidth(); 
 // 移动的范围 
 mRange = (int) (mWidth * 0.6f); 
} 

@Override 
public int clampViewPositionHorizontal(View child, int left, int dx) { 
 Log.d(TAG, "clampViewPositionHorizontal 建议值left:" + left + " mRange:" + mRange); 
 if (left > mRange) { 
  left = mRange; 
 } else if (left < 0) { 
  left = 0; 
 } 
 return left; 
} 

@Override 
public int clampViewPositionVertical(View child, int top, int dy) { 
 Log.d(TAG, "clampViewPositionVertical 建议值top:" + top + " mRange:" + mRange); 
 if (top > mRange) { 
  top = mRange; 
 } else if (top < 0) { 
  top = 0; 
 } 
 return top; 
} 

/** 
 * 当View的位置发生变化的时候,处理要做的事情(更新状态,伴随动画,重绘界面) 
 * 此时,View已经发生了位置的改变 
 * 
 * @param changedView 改变位置的View 
 * @param left  新的左边值 
 * @param top   新的上边值 
 * @param dx   水平方向的变化量 
 * @param dy   垂直方向的变化量 
 */ 
@Override 
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) { 
 Log.d(TAG, "位置发生变化onViewPositionChanged:" + "新的左边值left: " + left + " 水平方向的变化量dx:" + dx 
   + " 新的上边值top:" + top + " 垂直方向的变化量dy:" + dy); 
 super.onViewPositionChanged(changedView, left, top, dx, dy); 
 // 为了兼容低版本, 每次修改值之后, 进行重绘 
 invalidate(); 
} 

@Override 
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) { 
 super.onViewPositionChanged(changedView, left, top, dx, dy); 
 //获取最新的left坐标 
 int newLeft = left; 
 if (changedView == mLeftContent) { 
  //如果滑动的是mLeftContent,则将其水平变化量dx传递给mMainContent,记录在newLeft中 
  newLeft = mMainContent.getLeft() + dx; 
 } 
 //矫正范围 
 if (newLeft > mRange) { 
  newLeft = mRange; 
 } else if (newLeft < 0) { 
  newLeft = 0; 
 } 
 //再次判断,限制mLeftContent的滑动 
 if (changedView == mLeftContent) { 
  //强制将mLeftContent的位置摆会原来的位置,这里通过layout方法传入左,上,右,下坐标来实现 
  //当然方法不限于这一种,例如还可以通过scrollTo(x,y)方法 
  mLeftContent.layout(0, 0, mWidth, mHeight); 
  //改变mMainContent的位置 
  mMainContent.layout(newLeft, 0, newLeft + mWidth, mHeight); 
 } 
 // 为了兼容低版本, 每次修改值之后, 进行重绘 
 invalidate(); 
} 

/** 
 * 当被拖拽的View释放的时候回调,通常用于执行收尾的操作(例如执行动画) 
 * @param releasedChild 被释放的View 
 * @param xvel 水平方向的速度,向右释放为正值,向左为负值 
 * @param yvel 垂直方向的速度,向下释放为正值,向上为负值 
 */ 
@Override 
public void onViewReleased(View releasedChild, float xvel, float yvel) { 
 Log.d(TAG, "View被释放onViewReleased:" + "释放时水平速度xvel:" + xvel + " 释放时垂直速度yvel:" + yvel); 
 super.onViewReleased(releasedChild, xvel, yvel); 
} 

@Override 
public void onViewReleased(View releasedChild, float xvel, float yvel) { 
 Log.d(TAG, "View被释放onViewReleased:" + "释放时水平速度xvel:" + xvel + " 释放时垂直速度yvel:" + yvel); 
 super.onViewReleased(releasedChild, xvel, yvel); 
 if (xvel > 0 || (xvel == 0 && mMainContent.getLeft() > mRange / 2.0f)) { 
  //打开mLeftContent,即mMainContent的x=mRange 
  mMainContent.layout(mRange, 0, mRange + mWidth, mHeight); 
 } else { 
  //关闭mLeftContent,即mMainContent的x=0 
  mMainContent.layout(0, 0, mWidth, mHeight); 
 } 
} 

@Override 
public void onViewReleased(View releasedChild, float xvel, float yvel) { 
 Log.d(TAG, "View被释放onViewReleased:" + "释放时水平速度xvel:" + xvel + " 释放时垂直速度yvel:" + yvel); 
 super.onViewReleased(releasedChild, xvel, yvel); 
 if (xvel > 0 || (xvel == 0 && mMainContent.getLeft() > mRange / 2.0f)) { 
  //打开mLeftContent,即mMainContent的x=mRange 
  if (dragHelper.smoothSlideViewTo(mMainContent, mRange, 0)) { 
   // 返回true代表还没有移动到指定位置, 需要刷新界面. 
   // 参数传this(child所在的ViewGroup) 
   ViewCompat.postInvalidateOnAnimation(DragLayout.this); 
  } 
 } else { 
  //关闭mLeftContent,即mMainContent的x=0 
  if (dragHelper.smoothSlideViewTo(mMainContent, 0, 0)) { 
   ViewCompat.postInvalidateOnAnimation(DragLayout.this); 
  } 
 } 
@Override 
public void computeScroll() { 
 super.computeScroll(); 
 // 2. 持续平滑动画 (高频率调用) 
 if(dragHelper.continueSettling(true)){ 
  // 如果返回true, 动画还需要继续执行 
  ViewCompat.postInvalidateOnAnimation(this); 
 } 
}