Question

我有一个异步任务，我想每10秒重复一次，以便将焦点移回到Android应用程序的用户界面中。

我尝试使用java.util.Timer和TimerTask，但应用程序崩溃。如您所见，它在for循环中有效，但我需要每10秒重复一次。这样做...即使我包含Thread.Sleep（10000），延迟，while循环也不起作用。

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.*;
import android.os.AsyncTask;

public class MainActivity extends AppCompatActivity {

    TextView statusDisplay,display;        

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        display=(TextView)findViewById(R.id.display);
        display.setText("display");
        statusDisplay=(TextView)findViewById(R.id.statusDisplay);
        statusDisplay.setText("status");

        

        //I need to make this call every 10 secs
        
          new MyAsyncTask().execute("start");//Works fine as a single execution
        

    }


    //Our AsynTask
    // Specify your own types                              <params,progress,result>
    private class MyAsyncTask extends AsyncTask<String,Integer,Integer>
    {
        String status="Task being setup";
        int counter=0;

        //Step 1 that is executed for setting up our Asynchronous task
        @Override
        protected void onPreExecute()
        {
            super.onPreExecute();
            display.setText(status);
            statusDisplay.setText(String.valueOf(counter));
        }

        //Step 2 runs in the background and is only executed once
        //So put whatever computations including access to the Network inside this method
        //Do not make any calls to the UI from inside this method as its running in the background
        @Override
        protected Integer doInBackground(String[] params)
        {
            try{

                status=params[0];

                for(int i = 0;i<10;i++){
                    counter++;
                    status = "Task Running" + " " + String.valueOf(counter) + " " + "of" + " " + "10";
                    publishProgress(counter);//Calls onProgressUpdate
                    Thread.sleep(1000);
                }
            }
            catch(InterruptedException ex){

            }

            status = "Task completed";
            return counter;
        }


        //Step 3 called when we make a call to publishProgress in doInBackground
        @Override
        protected void onProgressUpdate(Integer[] values)
        {
            super.onProgressUpdate(values);

            display.setText(String.valueOf(values[0]));
            statusDisplay.setText(status);
        }


        //Step 4 Called after completion of doInBackground. Its return value is passed on to this method
        //Make final update changes to your UI at this step

        @Override
        protected void onPostExecute(Integer result)
        {
            super.onPostExecute(result);

            display.setText(String.valueOf(result));
            statusDisplay.setText(status);
        }
    }
}

Answer 1

您可以使用ScheduledExecutorService：

private ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
Runnable yourTaskRunner = new Runnable() {
    public void run() { new MyAsyncTask().execute("start"); }
}
scheduler.scheduleAtFixedRate(yourTaskRunner, 0, 10, TimeUnits.SECONDS);

described here的四种方式之一。

Answer 2

这是香港专业教育学院的尝试，但没有看到延迟。它只会定期重新运行

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.*;
import android.os.AsyncTask;
import android.os.Handler;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class MainActivity extends AppCompatActivity {

    TextView statusDisplay,display;
    int x=0;
    Handler handler = new Handler();
    int stopcondition=0;
    ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        display=(TextView)findViewById(R.id.display);
        display.setText("display");
        statusDisplay=(TextView)findViewById(R.id.statusDisplay);
        statusDisplay.setText("status");

        //new MonitorSecurityStatus().execute("start");//This works fine


        //handler.post(rerunCode);//A)Runs periodically and terminates when stop-condition occurs but we don't see the 5 sec delay
        //handler.postDelayed(rerunCode,5000);//B) Executes rerunCode after 5 sec delay we don't need this

        scheduler.scheduleWithFixedDelay(rerunCode,0,5000, TimeUnit.MILLISECONDS);//C) Behaves same as A)
    }

private Runnable rerunCode = new Runnable() {
    @Override
    public void run()
    {
        //handler.postDelayed(this,5000);//A) We dont see the 5 secs delay behaves same as if this declaration was inside else-if
        stopcondition++;
        if(stopcondition==10){
            handler.removeCallbacks(this);
        }
        else if(stopcondition<10)
        {
            new MonitorSecurityStatus().execute("start");
            handler.postDelayed(this,5000);//A) We dont see the 5 secs delay
        }
    }
};

如何定期重复执行异步任务？

2 个答案: