java - Android Studio 错误 : Can't create handler inside thread that has not called Looper. 准备()

Question

我试图在 AsyncTask Activity 中每隔 X 秒运行一段代码，但在进入任何打印语句之前它就崩溃了。我不确定它为什么崩溃，但我也发布了我收到的错误。有人有主意吗？太感谢了!

public class AppListener extends AsyncTask<String, String, String> {

@Override
protected String doInBackground(String... uri) {


    final Handler h = new Handler();
    final int delay = 5000; //milliseconds

    h.postDelayed(new Runnable() {
        public void run() {


            try {

                String msg_received = null;

                System.out.println("LISTENING FOR LAST INSTALLED APP");


                System.out.println("TRY");

                Socket socket = new Socket("85.190.178.23", 5050);

                // Get data sent through socket
                DataInputStream DIS = new DataInputStream(socket.getInputStream());

                System.out.println("DataInputStream Started");

                // read data that got sent
                msg_received = DIS.readUTF();

                System.out.println("Message from server" + msg_received);

                // Might not want to close socket, or only the first string will be sent and none after
                socket.close();


            }

            catch (Exception e) {
                System.out.println("Did not receive string");
            }




            h.postDelayed(this, delay);
        }
    }, delay);



    String msg_received = null;
    return msg_received;


}

}

我的错误

原因:java.lang.RuntimeException:无法在未调用 Looper.prepare() 的线程内创建处理程序

以下是我如何让循环每 X 秒执行一次，而不干扰我的 GUI(如果对其他人有帮助的话):我没有单独的类，而是在我的主要 Activity 中发布了我的代码。应用程序启动

public class MainActivity extends FragmentActivity{



private Thread repeatTaskThread;


// called when the activity is first created
@Override
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);


  // Go into loop that is repeated every X seconds
  RepeatTask();
}




private void RepeatTask()
{
  repeatTaskThread = new Thread()
  {
     public void run()
     {
        while (true)
        {

         //Post your code here that you want repeated every X seconds
         // My "try" and "catch" statements from above got inserted here


           try
           {
              // Sleep for 5 seconds
              Thread.sleep(5000);
           }
           catch (Exception e)
           {
              e.printStackTrace();
           }
        }
     };
  };
  repeatTaskThread.start();

}
}

Answer 1

更新:当您启动 AsyncTasks doInBackground 时，您正在启动一个后台线程。如果您想延迟发布 AsyncTask 的 doInBackground，那么您根本不应该使用 AsyncTask。您应该只需要使用带有 postDelayed 的 Handler，它将为您创建一个后台线程。看起来在您的代码中，您尝试在 AsyncTask 的后台线程中同时启动一个带有处理程序的新线程。

完全摆脱 AsyncTask，并将此代码包含在您的 Activity 中:

final Handler h = new Handler();
final int delay = 5000; //milliseconds

h.postDelayed(new Runnable() {
    public void run() {


        try {

            String msg_received = null;

            System.out.println("LISTENING FOR LAST INSTALLED APP");


            System.out.println("TRY");

            Socket socket = new Socket("85.190.178.23", 5050);

            // Get data sent through socket
            DataInputStream DIS = new DataInputStream(socket.getInputStream());

            System.out.println("DataInputStream Started");

            // read data that got sent
            msg_received = DIS.readUTF();

            System.out.println("Message from server" + msg_received);

            // Might not want to close socket, or only the first string will be sent and none after
            socket.close();


        }

        catch (Exception e) {
            System.out.println("Did not receive string");
        }




        h.postDelayed(this, delay);
    }
}, delay);



String msg_received = null;
return msg_received;


    }