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multithreading – Error calling toast from Service Android

Posted by: admin June 15, 2020 Leave a comment

Questions:

Possible Duplicate:
Android Toast started from Service only displays once

I’m using Service Android defined in android.app.Service.

I call this Service (myService) from an Activity.

MyService is:

public class myService extends Service{

 public IBinder onBind(Intent intent){
    return null;
}

public void onCreate(){
    super.onCreate();
    TimerTask task = new TimerTask(){
        public void run(){
            Log.i("test","service running");
            checkDate();            
        }           
    };
    timer = new Timer();
    timer.schedule(task, 0, 20000);
}

 public void checkDate(){
    Toast toast = Toast.makeText(this, "SIMPLE MESSAGE!", Toast.LENGTH_LONG);
    toast.show();
}

}

The method checkDate() resides in the class myService.

The error produced is:

 09-19 15:41:35.267: E/AndroidRuntime(2026): FATAL EXCEPTION: Timer-0
 09-19 15:41:35.267: E/AndroidRuntime(2026): java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
 09-19 15:41:35.267: E/AndroidRuntime(2026):    at android.os.Handler.<init>(Handler.java:121)
 09-19 15:41:35.267: E/AndroidRuntime(2026):    at android.widget.Toast$TN.<init>(Toast.java:310)
 09-19 15:41:35.267: E/AndroidRuntime(2026):    at android.widget.Toast.<init>(Toast.java:84)
 09-19 15:41:35.267: E/AndroidRuntime(2026):    at android.widget.Toast.makeText(Toast.java:226)
How to&Answers:

TimerTask runs in a separate thread. Toast.makeText() must be executed from a thread that has established a Handler/Looper. Basically this means you need to make the toast on a thread that has the standard Android message/event dispatcher running in it.

Easiest way to do this would be in your checkDate() method:

runOnUiThread(new Runnable() {
    public void run() {
        Toast toast = Toast.makeText(this, "SIMPLE MESSAGE!", Toast.LENGTH_LONG);
        toast.show();
    }
 });

EDIT: I’m an idiot, that’s not right. You can’t call runOnUiThread() from a Service context

You need to use a Handler for this. In your service:

private Handler handler;

in onCreate() of your service:

handler = new Handler();

in checkDate() method:

handler.post(new Runnable() {
    public void run() {
        Toast toast = Toast.makeText(myService.this, "SIMPLE MESSAGE!", Toast.LENGTH_LONG);
        toast.show();
    }
 });

Answer:

You’re calling it from a worker thread. You need to call Toast.makeText() (and most other functions dealing with the UI) from within the main thread. You could use a handler, for example.

You need to call Toast.makeText(…) from the UI thread:

activity.runOnUiThread(new Runnable() {
  public void run() {
    Toast.makeText(activity, "Hello", Toast.LENGTH_SHORT).show();
  }
});