Android应用开发——退出确认对话框 后退键捕捉

//这是退出是确认对话框出现的函数

	private Dialog ExitDialog(Context context) {  
	    AlertDialog.Builder builder = new AlertDialog.Builder(context);  
	    builder.setIcon(R.drawable.icon);  
	    builder.setTitle("系统信息");  
	    builder.setMessage("确定要退出程序吗?");  
	    builder.setPositiveButton("确定",  
	            new DialogInterface.OnClickListener() {  
	                public void onClick(DialogInterface dialog, int whichButton) {    	                	
	                	 System.exit(0);
	                }  
	            });  
	    builder.setNegativeButton("取消",  
	            new DialogInterface.OnClickListener() {  
	                public void onClick(DialogInterface dialog, int whichButton) {  
	                }  
	            });  
	    return builder.create();  
	} 
	

//这是对于后退键的捕捉函数，应该熟识此类函数的应用方法

public boolean onKeyDown(int keyCode, KeyEvent event) {  
     if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {  
         ExitDialog(MainActivity.this).show();  
         //this.finish();
         return true;
     } 
     return false;
 }