android监听返回按钮事件

用户在点击手机的返回按钮时，默认是推出当前的activty，但是有时用户不小心按到返回，所以需要给用户一个提示，这就需要重写onkeydown事件，实现的效果如下：

@Override 
    public void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.main); 
    } 
    protected void dialog() { 
        AlertDialog.Builder builder = new Builder(HanderTestActivty.this); 
        builder.setMessage("确定要退出吗?"); 
        builder.setTitle("提示"); 
        builder.setPositiveButton("确认", 
                new android.content.DialogInterface.OnClickListener() { 
                    @Override 
                    public void onClick(DialogInterface dialog, int which) { 
                        dialog.dismiss(); 
                        HanderTestActivty.this.finish(); 
                    } 
                }); 
        builder.setNegativeButton("取消", 
                new android.content.DialogInterface.OnClickListener() { 
                    @Override 
                    public void onClick(DialogInterface dialog, int which) { 
                        dialog.dismiss(); 
                    } 
                }); 
        builder.create().show(); 
    } 
    @Override 
    public boolean onKeyDown(int keyCode, KeyEvent event) { 
        if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) { 
            dialog(); 
            return false; 
        } 
        return false; 
    }