How to show toast in AsyncTask in doInBackground

Question

In one of my activities I'm using AsyncTask. In doInBackground() I'm making calls to various methods. In one of these methods I'm getting an exception, so in the catch block I want to show the error in the Toast. I know I can use Log, but still I prefer Toast. So, how can I use Toast in AsyncTask in doInBackground()?

why you are not retuning error to onPostExecute from doInBackground() and then so this error in a toast from onPostExecute — ρяσѕρєя K, Dec 09 '12 at 18:44
you can't modify the UI from the doInBackground() method, try to return some result, and test on that result in the onPostExecute() method , if it is , so show the Toast — Houcine, Dec 09 '12 at 18:44
@Sam : easy man !! i didn't voted down , i've just added my comment, i know that you can give access in `doInBackground()` , but it isn't recommended to do that, if so , then why there is methods `onProgressUpdate()` and `onPostExecute()` ?? — Houcine, Dec 09 '12 at 21:00
Consider the user here. The real answer is that you probably shouldn't be throwing a Toast in the first place. As a developer it might be nice to see updates to whatever it is you are trying to do in the background. But does your *user* really care? You are fighting the framework when you try to update the UI from `doInBackground`. — tir38, Feb 02 '15 at 00:55

score 17 · Answer 1 · answered Dec 09 '12 at 18:41

return from doInBackground as

protected String doInBackground(String... params){
    //some code
    try{
       //some code
     }catch(Exception e){
        return "Exception Caught";
     }
     return someValidResult;
}

protected void onPostExecute(String result){
    if(result.equalsIgnoreCase("Exception Caught")){
       //Display Toast
    }else{
       // // whatever you wana do with valid result
    }
}

score 13 · Accepted Answer · edited Dec 10 '12 at 10:00

13

You could wrap the Toast in runOnUIThread() but this isn't the best solution.
You should set a boolean flag in the catch block when an error occurs, then display an appropriate Toast in onProgressUpdate(), onPostExecute(), or any of the other methods with UI access whenever the flag is true.

edited Dec 10 '12 at 10:00

Houcine

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answered Dec 09 '12 at 18:33

Sam

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I don't understand that either... +1'ed it – Ahmad Dec 09 '12 at 19:05
Which Context should be passed to toast **getBaseContext()** or **getApplication()** Context? – oturan Mar 06 '16 at 07:54

score 6 · Answer 3 · edited May 27 '14 at 11:53

6

Write the following code where you have to show toast in doInBackground() method

runOnUiThread(new Runnable() {

public void run() {

  Toast.makeText(getApplicationContext(), "Example for Toast", Toast.LENGTH_SHORT).show();

   }
});

BTW: if you are using Fragments, you need to call runOnUiThread(...) through your activity:

getActivity().runOnUiThread(...)

edited May 27 '14 at 11:53

Wicked161089

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answered Nov 20 '13 at 13:37

Harshad07

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score 3 · Answer 4 · answered Dec 09 '12 at 18:38

3

You can display it in a method, that has access to the UI thread like onPreExecute(), onProgressUpdate() and onPostExecute()

answered Dec 09 '12 at 18:38

Ahmad

69,608
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score 3 · Answer 5 · answered Jun 03 '14 at 08:29

Create a handler object and execute all your Toast messages using that.

@Override
protected Void doInBackground(Void... params) {

    Handler handler=new handler();
    handler=  new Handler(context.getMainLooper());
    handler.post( new Runnable(){
        public void run(){
            Toast.makeText(context, "Created a server socket",Toast.LENGTH_LONG).show(); 
        }
    });
  }

score 1 · Answer 6 · edited Jul 14 '15 at 05:54

1

runOnUiThread(new Runnable() {

public void run() {

  Toast.makeText(getApplicationContext(), "Example for Toast", Toast.LENGTH_SHORT).show();

   }
});

is working perfectly fine to show toast in doInBackground() method

edited Jul 14 '15 at 05:54

Rasel

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answered Feb 12 '14 at 10:27

user3073127

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1

score 0 · Answer 7 · answered Jul 14 '15 at 05:32

0

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

answered Jul 14 '15 at 05:32

Rasel

5,488
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score 0 · Answer 8 · answered Aug 05 '15 at 06:43

try this code

void showError(final String err) {
    runOnUiThread(new Runnable() {
        public void run() {
            Toast.makeText(downloadprogress.this, err + "error in download", Toast.LENGTH_LONG)
                    .show();
        }
    });
  }

score 0 · Answer 9 · answered Jan 05 '20 at 13:49

If you have to declare anything related to Thread, then it must be outside the runOnUiThread() method, then only it is going to execute,

    @Override
    protected String doInBackground(String... strings) {
        for(int i=0; i<10; i++) {

            runOnUiThread(new Runnable() {
                public void run() {
                    Toast.makeText(getApplicationContext(), "Example for Toast "+i, Toast.LENGTH_SHORT).show();
                }
            });

            try {
                Thread.sleep(10);
            } catch (Exception e) {}
        }

        return "";
    }

How to show toast in AsyncTask in doInBackground

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