Android实现退出界面弹出提示对话框

<?xml version="1.0" encoding="utf-8"?>  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:id="@+id/layout1"   android:gravity="center_horizontal"   >    <Button     android:id="@+id/button1"     android:layout_width="wrap_content"     android:layout_height="wrap_content"      android:text="退出"/> </LinearLayout> 

package com.example.test;    import android.app.Activity; import android.app.AlertDialog; import android.content.DialogInterface; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button;   public class MainActivity extends Activity {      @Override    public void onCreate(Bundle savedInstanceState) {      super.onCreate(savedInstanceState);      setContentView(R.layout.main);           Button button=(Button)findViewById(R.id.button1);     //为"退出"按钮添加单击事件监听器     button.setOnClickListener(new OnClickListener() {              @Override       public void onClick(View view) {         AlertDialog alert=new AlertDialog.Builder(MainActivity.this).create();         alert.setIcon(R.drawable.stop);         alert.setTitle("退出？");         alert.setMessage("真的要退出本软件吗？");         //添加取消按钮         alert.setButton(DialogInterface.BUTTON_NEGATIVE,"不",new DialogInterface.OnClickListener() {                      @Override           public void onClick(DialogInterface dialog, int which) {             // TODO Auto-generated method stub                        }         });         //添加"确定"按钮         alert.setButton(DialogInterface.BUTTON_POSITIVE,"是的", new DialogInterface.OnClickListener() {                      @Override           public void onClick(DialogInterface arg0, int arg1) {              finish();           }         });         alert.show();       }     });   }  }