127

How can I display Toast messages from a thread?

Saket
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Arutha
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14 Answers14

261

You can do it by calling an Activity's runOnUiThread method from your thread:

activity.runOnUiThread(new Runnable() {
    public void run() {
        Toast.makeText(activity, "Hello", Toast.LENGTH_SHORT).show();
    }
});
Lauri Lehtinen
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    I'm not sure I understand how to do this. I have my existing public void run(). I tried putting this code there. I know that's not right because it didn't work, but I am really stuck. – SwimBikeRun Mar 04 '12 at 06:04
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    Is "activity" passed to the non-ui-thread in its constructor? What is the right way to get the activity object that you are using from within the separate thread? – snapfractalpop Mar 15 '12 at 17:26
  • Set the `Thread` object's reference to the `Activity` in the `Activity`'s `onResume`. Unset it in the `Activity`'s `onPause`. Do both under a `synchronized` lock that both the `Activity` and `Thread` respect. – JohnnyLambada Apr 24 '12 at 05:55
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    sometimes there is no access to ```Activity``` instance, you can use simple helper-class instead, see here: http://stackoverflow.com/a/18280318/1891118 – Oleksii K. Aug 28 '13 at 09:27
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    I've usually found that `MyActivity.this.runOnUiThread()` works just fine from within an inner `Thread`/`AsyncTask`. – Anthony Atkinson Apr 30 '14 at 17:39
  • what is the syntax for this in Kotlin? – Craig P Aug 30 '18 at 09:41
  • `runOnUiThread` does not seem to be available in the newer version of android api. – Ryan Oct 19 '21 at 00:36
72

I like to have a method in my activity called showToast which I can call from anywhere...

public void showToast(final String toast)
{
    runOnUiThread(() -> Toast.makeText(MyActivity.this, toast, Toast.LENGTH_SHORT).show());
}

I then most frequently call it from within MyActivity on any thread like this...

showToast(getString(R.string.MyMessage));
mjaggard
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    Thanks, I'm adding this most activities now. – Gene Myers Dec 01 '13 at 17:25
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    For TOAST, always use Application Context, not Activity Context! – Yousha Aleayoub Sep 21 '15 at 08:35
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    @YoushaAleayoub why? – OneWorld Feb 16 '16 at 09:44
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    @OneWorld, proofs: 1- For a toast message, the Google Dev Guide uses the application context and explicitly say's to use it. 2- http://stackoverflow.com/a/4128799/1429432 3- http://stackoverflow.com/a/10347346/1429432 4- https://groups.google.com/d/msg/android-developers/3i8M6-wAIwM/EQOdAZKxsQYJ – Yousha Aleayoub Feb 16 '16 at 17:30
  • @YoushaAleayoub There is a lot of discussion and guessing in the links you provided. E.g. RomainGuy says there is no memory leak in your proof no. 4. Some of the links are from the early days of Android in 2009. Also people say in the other links that you can use both contexts. Activity and application. Maybe you have a more up to date real evidence based proof? Do you have a link for 1? – OneWorld Feb 22 '16 at 10:36
  • 1- outdated? lol dude they wont be updated, and you CANT find any updated article in this case. So follow the old(?) rules if you dont have any idea or cant prove it. – Yousha Aleayoub Feb 22 '16 at 15:42
  • If Google suggested us to use ApplicationContext, then they should make it easier to access it, and stop returning null in any case. e.g. fragment.getApplicationContext(). – Kimi Chiu Nov 02 '16 at 04:12
34

This is similar to other answers, however updated for new available apis and much cleaner. Also, does not assume you're in an Activity Context.

public class MyService extends AnyContextSubclass {

    public void postToastMessage(final String message) {
        Handler handler = new Handler(Looper.getMainLooper());

        handler.post(new Runnable() {

            @Override
            public void run() {
                Toast.makeText(getContext(), message, Toast.LENGTH_LONG).show();
            }
        });
    }
}
MobA11y
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26

One approach that works from pretty much anywhere, including from places where you don't have an Activity or View, is to grab a Handler to the main thread and show the toast:

public void toast(final Context context, final String text) {
  Handler handler = new Handler(Looper.getMainLooper());
  handler.post(new Runnable() {
    public void run() {
      Toast.makeText(context, text, Toast.LENGTH_LONG).show();
    }
  });
}

The advantage of this approach is that it works with any Context, including Service and Application.

topher217
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Mike Laren
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  • What if your app is backgrounded, and a service thread calls this code, will the toast display when the app is foregrounded? I'm curios what happens to the main application thread when the app backgrounded. Does it pause, and not execute tasks in the event loop? And then resume? – the_prole Oct 01 '21 at 15:24
10

Like this or this, with a Runnable that shows the Toast. Namely,

Activity activity = // reference to an Activity
// or
View view = // reference to a View

activity.runOnUiThread(new Runnable() {
    @Override
    public void run() {
        showToast(activity);
    }
});
// or
view.post(new Runnable() {
    @Override
    public void run() {
        showToast(view.getContext());
    }
});

private void showToast(Context ctx) {
    Toast.makeText(ctx, "Hi!", Toast.LENGTH_SHORT).show();
}
yanchenko
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6

Sometimes, you have to send message from another Thread to UI thread. This type of scenario occurs when you can't execute Network/IO operations on UI thread.

Below example handles that scenario.

  1. You have UI Thread
  2. You have to start IO operation and hence you can't run Runnable on UI thread. So post your Runnable to handler on HandlerThread
  3. Get the result from Runnable and send it back to UI thread and show a Toast message.

Solution:

  1. Create a HandlerThread and start it
  2. Create a Handler with Looper from HandlerThread:requestHandler
  3. Create a Handler with Looper from Main Thread: responseHandler and override handleMessage method
  4. post a Runnable task on requestHandler
  5. Inside Runnable task, call sendMessage on responseHandler
  6. This sendMessage result invocation of handleMessage in responseHandler.
  7. Get attributes from the Message and process it, update UI

Sample code:

    /* Handler thread */

    HandlerThread handlerThread = new HandlerThread("HandlerThread");
    handlerThread.start();
    Handler requestHandler = new Handler(handlerThread.getLooper());

    final Handler responseHandler = new Handler(Looper.getMainLooper()) {
        @Override
        public void handleMessage(Message msg) {
            //txtView.setText((String) msg.obj);
            Toast.makeText(MainActivity.this,
                    "Runnable on HandlerThread is completed and got result:"+(String)msg.obj,
                    Toast.LENGTH_LONG)
                    .show();
        }
    };

    for ( int i=0; i<5; i++) {
        Runnable myRunnable = new Runnable() {
            @Override
            public void run() {
                try {

                    /* Add your business logic here and construct the 
                       Messgae which should be handled in UI thread. For 
                       example sake, just sending a simple Text here*/

                    String text = "" + (++rId);
                    Message msg = new Message();

                    msg.obj = text.toString();
                    responseHandler.sendMessage(msg);
                    System.out.println(text.toString());

                } catch (Exception err) {
                    err.printStackTrace();
                }
            }
        };
        requestHandler.post(myRunnable);
    }

Useful articles:

handlerthreads-and-why-you-should-be-using-them-in-your-android-apps

android-looper-handler-handlerthread-i

Ravindra babu
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5
  1. Get UI Thread Handler instance and use handler.sendMessage();
  2. Call post() method handler.post();
  3. runOnUiThread()
  4. view.post()
Ravindra babu
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Kerwin You
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3

You can use Looper to send Toast message. Go through this link for more details.

public void showToastInThread(final Context context,final String str){
    Looper.prepare();
    MessageQueue queue = Looper.myQueue();
    queue.addIdleHandler(new IdleHandler() {
         int mReqCount = 0;

         @Override
         public boolean queueIdle() {
             if (++mReqCount == 2) {
                  Looper.myLooper().quit();
                  return false;
             } else
                  return true;
         }
    });
    Toast.makeText(context, str,Toast.LENGTH_LONG).show();      
    Looper.loop();
}

and it is called in your thread. Context may be Activity.getContext() getting from the Activity you have to show the toast.

Ravindra babu
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Vinoj John Hosan
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2

I made this approach based on mjaggard answer:

public static void toastAnywhere(final String text) {
    Handler handler = new Handler(Looper.getMainLooper());
    handler.post(new Runnable() {
        public void run() {
            Toast.makeText(SuperApplication.getInstance().getApplicationContext(), text, 
                    Toast.LENGTH_LONG).show();
        }
    });
}

Worked well for me.

Ângelo Polotto
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2

Kotlin Code with runOnUiThread

runOnUiThread(
        object : Runnable {
            override fun run() {
                Toast.makeText(applicationContext, "Calling from runOnUiThread()", Toast.LENGTH_SHORT)  
            }
        }
)
Pratik Dodiya
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0

I encountered the same problem:

E/AndroidRuntime: FATAL EXCEPTION: Thread-4
              Process: com.example.languoguang.welcomeapp, PID: 4724
              java.lang.RuntimeException: Can't toast on a thread that has not called Looper.prepare()
                  at android.widget.Toast$TN.<init>(Toast.java:393)
                  at android.widget.Toast.<init>(Toast.java:117)
                  at android.widget.Toast.makeText(Toast.java:280)
                  at android.widget.Toast.makeText(Toast.java:270)
                  at com.example.languoguang.welcomeapp.MainActivity$1.run(MainActivity.java:51)
                  at java.lang.Thread.run(Thread.java:764)
I/Process: Sending signal. PID: 4724 SIG: 9
Application terminated.

Before: onCreate function

Thread thread = new Thread(new Runnable() {
    @Override
    public void run() {
        Toast.makeText(getBaseContext(), "Thread", Toast.LENGTH_LONG).show();
    }
});
thread.start();

After: onCreate function

runOnUiThread(new Runnable() {
    @Override
    public void run() {
        Toast.makeText(getBaseContext(), "Thread", Toast.LENGTH_LONG).show();
    }
});

it worked.

Paul Chu
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Languoguang
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0

java 11:

var handler = new Handler(Looper.getMainLooper);
handler.post(() -> Toast.makeText(your_context, "Hi!", Toast.LENGTH_SHORT).show());

Lambdas are available in java 8 though. var is introduced in java 11.

Ryan
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0

Contrary to almost every answer here, Toast#makeText and Toast#show do NOT have to run on the UI thread. The only requirement is that it runs on a thread that has called Looper#prepare.

The reasons for this is because toasts are handled and rendered by the OS, not the application. Internally, Toast#show makes a call to a system service to enqueue the toast.

This means the following code is valid

private static class MyThread extends Thread {
    public Handler handler;

    @Override
    public void run() {
        Looper.prepare();

        handler = new Handler(Looper.myLooper()) {
            public void handleMessage(Message msg) {
                super.handleMessage(msg);
            }
        };

        Looper.loop()
    }
}

final private MyThread t = new MyThread();
// start and wait for t to start looping

private void onClick() {
    t.handler.post(() -> Toast.makeText(this, "this works", Toast.LENGTH_SHORT).show());
}
0

Method in onCreate :

private void toastPublic(final String message){
    Handler handler = new Handler(Looper.getMainLooper());
    handler.post(new Runnable() {
       public void run() {
          Toast.makeText(getBaseContext(),""+message, 
             4 /*Toast.LENGTH_SHORT*/).show();
    }});
}

Next : use in inside Thread

alimogh
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