android - Android的IntentService类中的死循环或空闲代码

Question

我问这个问题是因为我的 Java 知识真的很低......我需要 需要使用这个新的 API 27 USSD 功能......下面是我正在尝试做的事情:

public class MyService extends IntentService {

    // BEGIN of MyService Class properties ****

    public static boolean jobInProgress = true;

    private Handler myHandler = new Handler() {
        public void handleMessage(Message msg) {
            super.handleMessage(msg); // I guess this will be on some message queue somewhere
        }
    };


    TelephonyManager  tm;

    // END of properties *************************************

    // BEGIN of MyService class abstract class methods implementation

    class MyCallback extends TelephonyManager.UssdResponseCallback{

        Context serviceContext;

        MyCallback (Context serviceContext){
            this.serviceContext = serviceContext;
        }
        public void onReceiveUssdResponse (TelephonyManager telephonyManager,
                                           String request,
                                           CharSequence response){
            //Here since it's a System callback I guess my this.tm == telephonyManager parameter right ?
            Toast.makeText(serviceContext, "Response from network is : " + response, Toast.LENGTH_LONG).show();

            MyService.jobInProgress = false;
        }

        public  void onReceiveUssdResponseFailed (TelephonyManager telephonyManager,
                                                    String request,
                                                    int failureCode){
            Toast.makeText(serviceContext, "USSD request failed with code " + failureCode, Toast.LENGTH_LONG).show();
            MyService.jobInProgress = false;
        }
    }
    // END of abstract methods implementation******************

    //BEGIN of MyService Class methods

    @Override
    public void onCreate() {
        super.onCreate();
        Toast.makeText(this, "Service is created.", Toast.LENGTH_LONG).show();
    }

    @Override 
    public void onDestroy() {
        super.onDestroy();
        Toast.makeText(this, "Service is destroyed", Toast.LENGTH_LONG).show();
    }

    @Override
    protected void onHandleIntent(@Nullable Intent intent) {
        doJob();
        while(jobInProgress){
            //I hang here to not call onDestroy to quickly...
        }
    }

    private void doJob(){

        //Get the instance of TelephonyManager
        this.tm =(TelephonyManager)getSystemService(this.TELEPHONY_SERVICE);


        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CALL_PHONE) != PackageManager.PERMISSION_GRANTED) {
            return;
        }
        //Don't know How to use sendUssdRequest second and thrid arguments. Below is what I have tried with no success
        this.tm.sendUssdRequest("#105*2#",new MyCallback(this),myHandler);
    }



    //END of class methods*****************************
}

我想要实现的目标是运行 USSD 请求并在 Toast 中打印结果。当我启动该服务时，它说服务按预期创建，它按预期进入 doJob() 方法，但在那之后，没有其他任何事情发生......该应用程序甚至没有崩溃......就好像输入了doJob()之后没有写指令...

你能帮我使这段代码工作吗？

Answer 1

它不起作用的原因是因为您同时使用了 Handler 和无限循环。

当您创建一个新的Handler 时，它会绑定(bind)到创建它的线程的线程/消息队列。因此，当您执行以下操作时:

while(jobInProgress){
            //I hang here to not call onDestroy to quickly...
  }

它将阻塞工作线程和 Handler。结果什么也没发生。

解决方案是使用普通服务并避免任何循环。

请记住，从 Android O 开始，您无法无休止地在后台运行您的服务。如果您的应用程序处于前台，则此方法将起作用。如果你想让它可靠地工作，请使用前台服务。