public boolean onKeyDown(int keyCode, KeyEvent event)

 @Override
 2     public boolean onKeyDown(int keyCode, KeyEvent event) {
 3         // TODO Auto-generated method stub
 4         
 5         if(keyCode==KeyEvent.KEYCODE_BACK){
 6             //弹出确定退出对话框
 7             new AlertDialog.Builder(this)
 8             .setTitle("退出")
 9             .setMessage("确定退出吗？")
10             .setPositiveButton("确定", new DialogInterface.OnClickListener() {
11                 
12                 @Override
13                 public void onClick(DialogInterface dialog, int which) {
14                     // TODO Auto-generated method stub
15                     Intent exit = new Intent(Intent.ACTION_MAIN);
16                     exit.addCategory(Intent.CATEGORY_HOME);
17                     exit.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
18                     startActivity(exit);
19                     System.exit(0);
20                 }
21             })
22             .setNegativeButton("取消", new DialogInterface.OnClickListener() {
23                 
24                 @Override
25                 public void onClick(DialogInterface dialog, int which) {
26                     // TODO Auto-generated method stub
27                     dialog.cancel();
28                 }
29             })
30             .show();
31             //这里不需要执行父类的点击事件，所以直接return
32             return true;
33         }
34         //继续执行父类的其他点击事件
35         return super.onKeyDown(keyCode, event);
36     }
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