Androidz之返回鍵退出程序

Android按返回鍵退出程序，沒什么好說的，直接貼代碼：

public boolean onKeyDown(int keyCode, KeyEvent event) {
            if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
                // 確認對話框
                final AlertDialog isExit = new AlertDialog.Builder(this).create();
                // 對話框標題
                isExit.setTitle("系統提示");
                // 對話框消息
                isExit.setMessage("確定要退出嗎?");
                // 實例化對話框上的按鈕點擊事件監聽
                DialogInterface.OnClickListener listener = new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {
                        switch (which) {
                        case AlertDialog.BUTTON1:// "確認"按鈕退出程序


                         NotificationManager notificationManager = (NotificationManager) MainActivity.this 
                            .getSystemService(NOTIFICATION_SERVICE); 
                            notificationManager.cancel(0); 
                            String packagename = getPackageName();
                            ActivityManager manager = (ActivityManager)getSystemService(ACTIVITY_SERVICE); 
                            finish();
                            if(getSystemVersion()<8){

                                manager.restartPackage(getPackageName()); 
                            }else{

                                manager.killBackgroundProcesses(packagename); 
                            }

                        break;
                    case AlertDialog.BUTTON2:// "取消"第二個按鈕取消對話框
                        isExit.cancel();
                        break;
                    default:
                        break;
                    }
                }
            };
            // 注冊監聽
            isExit.setButton("確定", listener);
            isExit.setButton2("取消", listener);
            // 顯示對話框
            isExit.show();
            return false;
        }
        return false;
    }</pre></span>