实现可拖拽View 工具类

package com.reone.loushi.customView;

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.WindowManager;
import android.widget.FrameLayout;

/**
* Created by wangxingsheng on 2017/1/15.
*
*/

public class DragLayout extends FrameLayout {
private int lastX;
private int lastY;
private int screenWidth;
private int screenHeight;

public DragLayout(Context context) {
super(context);
init();
}
public DragLayout(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public DragLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}
public void init() {
WindowManager wm = (WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE);
screenWidth = wm.getDefaultDisplay().getWidth();
screenHeight = wm.getDefaultDisplay().getHeight();
}

@Override
public boolean dispatchTouchEvent(MotionEvent event) {
int ea = event.getAction();
switch (ea) {
case MotionEvent.ACTION_DOWN:
lastX = (int) event.getRawX();
lastY = (int) event.getRawY();//按钮初始的横纵坐标
break;
case MotionEvent.ACTION_MOVE:
int dx = (int) event.getRawX()-lastX;
int dy = (int) event.getRawY()-lastY;//按钮被移动的距离
int l = getLeft()+dx;
int b = getBottom()+dy;
int r = getRight()+dx;
int t = getTop()+dy;
if(l<0){//处理按钮被移动到上下左右四个边缘时的情况，决定着按钮不会被移动到屏幕外边去
l = 0;
r = l+getWidth();
}
if(t<0){
t = 0;
b = t+getHeight();
}
if(r>screenWidth){
r = screenWidth;
l = r - getWidth();
}
if(b>screenHeight){
b = screenHeight;
t = b-getHeight();
}
layout(l, t, r, b);
lastX = (int) event.getRawX();
lastY = (int) event.getRawY();
postInvalidate();
break;
default:
break;
}
return super.dispatchTouchEvent(event);
}

}