android 实现可拖动的Button

DraftTest.java

package com.cn.lhq;import android.app.Activity;import android.os.Bundle;import android.util.DisplayMetrics;import android.util.Log;import android.view.MotionEvent;import android.view.View;import android.view.View.OnTouchListener;import android.widget.Button;import android.widget.Toast;public class DraftTest extends Activity {@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);DisplayMetrics dm = getResources().getDisplayMetrics();final int screenWidth = dm.widthPixels;final int screenHeight = dm.heightPixels - 50;final Button btn = (Button) findViewById(R.id.btn);btn.setOnTouchListener(new OnTouchListener() {int lastX, lastY;@Overridepublic boolean onTouch(View v, MotionEvent event) {// TODO Auto-generated method stubint ea = event.getAction();Log.i("TAG", "Touch:" + ea);switch (ea) {case MotionEvent.ACTION_DOWN:lastX = (int) event.getRawX();// 获取触摸事件触摸位置的原始X坐标lastY = (int) event.getRawY();break;case MotionEvent.ACTION_MOVE:int dx = (int) event.getRawX() - lastX;int dy = (int) event.getRawY() - lastY;int l = v.getLeft() + dx;int b = v.getBottom() + dy;int r = v.getRight() + dx;int t = v.getTop() + dy;// 下面判断移动是否超出屏幕if (l < 0) {l = 0;r = l + v.getWidth();}if (t < 0) {t = 0;b = t + v.getHeight();}if (r > screenWidth) {r = screenWidth;l = r - v.getWidth();}if (b > screenHeight) {b = screenHeight;t = b - v.getHeight();}v.layout(l, t, r, b);lastX = (int) event.getRawX();lastY = (int) event.getRawY();Toast.makeText(DraftTest.this,"当前位置：" + l + "," + t + "," + r + "," + b,Toast.LENGTH_SHORT).show();v.postInvalidate();break;case MotionEvent.ACTION_UP:break;}return false;}});}}

main.xml