Android 程序退出的办法以及监听并处理用户按下back键的方法
在Android中退出程序比较麻烦，尤其是在多个Activity的程序中，在2.2之前可以采用如下代码退出程序：
Java代码
package com.example.android_test01;import android.app.Activity;import android.app.AlertDialog;import android.app.AlertDialog.Builder;import android.content.DialogInterface;import android.content.DialogInterface.OnClickListener;import android.os.Bundle;import android.view.KeyEvent;import android.view.Menu;public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);}@Overridepublic boolean onKeyDown(int keyCode, KeyEvent event) {// TODO Auto-generated method stubSystem.out.println("你按下了back1");show_simple();return super.onKeyDown(keyCode, event);}//先调用的onKeyDown(int keyCode, KeyEvent event)方法，然后调用的onBackPressed()方法;@Overridepublic void onBackPressed() {// TODO Auto-generated method stubSystem.out.println("按下back，立刻退出activity时调用");super.onBackPressed();}public void show_simple(){AlertDialog.Builder builder=new Builder(this);builder.setTitle("欢迎使用本软件");builder.setPositiveButton("确定", new OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {// TODO Auto-generated method stub//退出应用;finish();}});builder.setNegativeButton("取消", new OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {// TODO Auto-generated method stub}});builder.create().show();}}