Android中退出程序的提示框

@Override  

    public boolean onKeyDown(int keyCode, KeyEvent event) {  

        if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {  

            dialog();  

            return true;  

        }  

        return true;  

    }  

protected void dialog() {  

        AlertDialog.Builder builder = new Builder(AccoutList.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();  

                //AccoutList.this.finish();  

                //System.exit(1);  

                android.os.Process.killProcess(android.os.Process.myPid());  

            }  

        });  

        builder.setNegativeButton("取消",  

        new android.content.DialogInterface.OnClickListener() {  

            @Override  

            public void onClick(DialogInterface dialog, int which) {  

                dialog.dismiss();  

            }  

        });  

        builder.create().show();  

    }