android基础学习之back键的监听和回到主页面

以前一直看别人写back键的监听，今天朋友问到自己了，然后自己说了一下，突然发现自己写不出来，然后百度了一下，不过就是一个onKeyDown的重写，。。。因为感觉代码太少，所以在添加监听的时候一个是关闭当前的activity，然后另外一个是跳转到桌面。ok，基本就这些，贴代码了

package com.jk.backdemo;import android.os.Bundle;import android.app.Activity;import android.app.AlertDialog;import android.app.AlertDialog.Builder;import android.content.DialogInterface;import android.content.DialogInterface.OnClickListener;import android.content.Intent;import android.text.AlteredCharSequence;import android.view.KeyEvent;import android.view.Menu;import android.widget.Toast;public class MainActivity extends Activity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);    }   @Overridepublic boolean onKeyDown(int keyCode, KeyEvent event) {//judge the keyCode   if(keyCode==KeyEvent.KEYCODE_BACK){   //create a AlertDialog.Builder's builder objectAlertDialog.Builder builder=new Builder(this);//set the titlebuilder.setTitle("确认退出");//set a postive button and add a listererbuilder.setPositiveButton("确定", new OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {//finish Activityfinish();}//set a negative button and add a listener}).setNegativeButton("取消", new OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {//init a intentIntent intent=new Intent();//add the Action propertyintent.setAction(intent.ACTION_MAIN);//Intent intent=new Intent(Intent.ACTION_MAIN);这句话和上面两句是等价的//add the Category propertyintent.addCategory(Intent.CATEGORY_HOME);//launch activitystartActivity(intent);}}).show();   }return true;}    }