ViewDragHelper类的基本使用

1 public static ViewDragHelper create (ViewGroup forParent, float sensitivity, ViewDragHelper.Callback cb)

  1 package com.example.ubuntu.viewdragermotion;
  2 
  3 import android.content.Context;
  4 import android.support.v4.view.MotionEventCompat;
  5 import android.support.v4.widget.ViewDragHelper;
  6 import android.util.AttributeSet;
  7 import android.view.MotionEvent;
  8 import android.view.View;
  9 import android.view.ViewGroup;
 10 import android.widget.LinearLayout;
 11 
 12 /**
 13  * Created by ubuntu on 15-12-1.
 14  */
 15 public class DragerMotionLayout extends LinearLayout {
 16     private View mChild_01;
 17     private ViewDragHelper mDragHelper = null;
 18     //设置ViewDragHelper的回调方法
 19     private ViewDragHelper.Callback mCallBack = new ViewDragHelper.Callback() {
 20         @Override
 21         public boolean tryCaptureView(View child, int pointerId) {
 22             //捕获view，被捕获之后，可以跟随手指的操作
 23             return child == mChild_01;
 24         }
 25 
 26         @Override
 27         public int clampViewPositionHorizontal(View child, int left, int dx) {
 28             //当用手拖动view的时候，设置view的水平方向上滑动距离
 29             final int leftPadding = child.getPaddingLeft();
 30             final int rightPadding = ((ViewGroup) child.getParent()).getWidth() - child.getWidth();
 31             return Math.min(rightPadding, Math.max(left, leftPadding));
 32         }
 33 
 34         @Override
 35         public int clampViewPositionVertical(View child, int top, int dy) {
 36             //当用手拖动view的时候，设置view的垂直方向上滑动距离
 37             final int topPadding = child.getPaddingTop();
 38             final int bottomPadding = ((ViewGroup) child.getParent()).getHeight() - child.getHeight();
 39             return Math.min(bottomPadding, Math.max(top,topPadding));
 40         }
 41 
 42         @Override
 43         public void onEdgeDragStarted(int edgeFlags, int pointerId) {
 44             //边缘滑动的时候，捕获view
 45             mDragHelper.captureChildView(mChild_01, pointerId);
 46         }
 47 
 48         @Override
 49         public void onViewReleased(View releasedChild, float xvel, float yvel) {
 50             //设置当手指离开的时候，view应该设置的位置，调用这个方法的时候，必须保证
 51             //computeScroll（）方法中使用的是ViewDragHelper.continueSettling(true)方法接管
 52             mDragHelper.settleCapturedViewAt(0,0);
 53             invalidate();
 54         }
 55     };
 56 
 57     public DragerMotionLayout(Context context) {
 58         this(context, null);
 59     }
 60 
 61     public DragerMotionLayout(Context context, AttributeSet attrs) {
 62         this(context, attrs, 0);
 63     }
 64 
 65     public DragerMotionLayout(Context context, AttributeSet attrs, int defStyleAttr) {
 66         super(context, attrs, defStyleAttr);
 67         init();
 68     }
 69 
 70     @Override
 71     protected void onFinishInflate() {
 72         super.onFinishInflate();
 73         mChild_01 = this.getChildAt(0);
 74     }
 75 
 76     private void init() {
 77         //初始化ViewDragHelper
 78         mDragHelper = ViewDragHelper.create(this, 1.0f, mCallBack);
 79         //使监听左边的边缘滑动
 80         mDragHelper.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT);
 81     }
 82 
 83     @Override
 84     public boolean onInterceptTouchEvent(MotionEvent ev) {
 85         int action = MotionEventCompat.getActionMasked(ev);
 86         if (action == MotionEvent.ACTION_UP || action == MotionEvent.ACTION_CANCEL) {
 87             mDragHelper.cancel();
 88             return false;
 89         }
 90         //ViewDragHelper接管事件的拦截
 91         return mDragHelper.shouldInterceptTouchEvent(ev);
 92     }
 93 
 94 
 95     @Override
 96     public boolean onTouchEvent(MotionEvent event) {
 97         //ViewDragHelper接管事件的处理
 98         mDragHelper.processTouchEvent(event);
 99         return true;
100     }
101 
102     @Override
103     public void computeScroll() {
104         //如果view处于STATE_SETTLING状态下，使用该方法接管
105         if(mDragHelper.continueSettling(true)){
106             invalidate();
107         }
108     }
109 }