Android AsyncTask [Can't create handler inside thread that has not called Looper.prepare()]
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3

29

I've created an image upload AsyncTask based on a function. And after uploading, I get this error on onPostExecute(). I read up some StackOverflow answers on Runnable yet I kept getting the error over and over again despite implementing a different solution.

My code :

class uploadFile extends AsyncTask<String, String, String> {
    private ProgressDialog pDialog;

    /**
     * --------------------------------------------------------------------
     * --------------------------------- Before starting background thread
     * Show Progress Dialog
     */
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(MainActivity.this);
        pDialog.setMessage("Uploading file");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(false);
        pDialog.show();
    }

    /**
     * --------------------------------------------------------------------
     * --------------------------------- getting all recent articles and
     * showing them in listview
     */
    @Override
    protected String doInBackground(String... args) {
        HttpURLConnection conn = null;
        DataOutputStream dos = null;
        DataInputStream inStream = null;
        String existingFileName = Environment.getExternalStorageDirectory()
                .getAbsolutePath() + "/mypic.png";
        String lineEnd = "\r\n";
        String twoHyphens = "--";
        String boundary = "*****";
        int bytesRead, bytesAvailable, bufferSize;
        byte[] buffer;
        int maxBufferSize = 1 * 1024 * 1024;
        String serverResponseMessage = "";
        String urlString = "http://google.info/imgupl/index.php";
        try {
            // ------------------ CLIENT REQUEST
            FileInputStream fileInputStream = new FileInputStream(new File(
                    existingFileName));
            // open a URL connection to the Servlet
            URL url = new URL(urlString);
            // Open a HTTP connection to the URL
            conn = (HttpURLConnection) url.openConnection();
            // Allow Inputs
            conn.setDoInput(true);
            // Allow Outputs
            conn.setDoOutput(true);
            // Don't use a cached copy.
            conn.setUseCaches(false);
            // Use a post method.
            conn.setRequestMethod("POST");
            conn.setRequestProperty("Connection", "Keep-Alive");
            conn.setRequestProperty("Content-Type",
                    "multipart/form-data;boundary=" + boundary);
            dos = new DataOutputStream(conn.getOutputStream());
            dos.writeBytes(twoHyphens + boundary + lineEnd);
            dos.writeBytes("Content-Disposition: form-data; name=\"uploadedfile\";filename=\""
                    + existingFileName + "\"" + lineEnd);
            dos.writeBytes(lineEnd);
            // create a buffer of maximum size
            bytesAvailable = fileInputStream.available();
            bufferSize = Math.min(bytesAvailable, maxBufferSize);
            buffer = new byte[bufferSize];
            // read file and write it into form...
            bytesRead = fileInputStream.read(buffer, 0, bufferSize);
            while (bytesRead > 0) {
                dos.write(buffer, 0, bufferSize);
                bytesAvailable = fileInputStream.available();
                bufferSize = Math.min(bytesAvailable, maxBufferSize);
                bytesRead = fileInputStream.read(buffer, 0, bufferSize);
            }
            // send multipart form data necesssary after file data...
            dos.writeBytes(lineEnd);
            dos.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);
            // close streams
            Integer serverResponseCode = conn.getResponseCode();
            serverResponseMessage = conn.getResponseMessage();
            Toast.makeText(getApplicationContext(), serverResponseMessage,
                    Toast.LENGTH_SHORT).show();
            Toast.makeText(getApplicationContext(),
                    serverResponseCode.toString(), Toast.LENGTH_SHORT)
                    .show();
            Log.e("Debug", "File is written");
            fileInputStream.close();
            dos.flush();
            dos.close();
        } catch (MalformedURLException ex) {
            Log.e("Debug", "error: " + ex.getMessage(), ex);
        } catch (IOException ioe) {
            Log.e("Debug", "error: " + ioe.getMessage(), ioe);
        }
        // ------------------ read the SERVER RESPONSE
        try {
            inStream = new DataInputStream(conn.getInputStream());

            while ((str = inStream.readLine()) != null) {
                Log.e("Debug", "Server Response " + str);
            }
            inStream.close();

        } catch (IOException ioex) {
            Log.e("Debug", "error: " + ioex.getMessage(), ioex);
        }
        return null;
    }

    /**
     * --------------------------------------------------------------------
     * --------------------------------- After completing background task
     * Dismiss the progress dialog
     **/
    protected void onPostExecute(String args) {
        // dismiss the dialog after getting all products
        pDialog.dismiss();
        MainActivity.this.runOnUiThread(new Runnable() {
            public void run() {
                Toast.makeText(MainActivity.this, "Hello", Toast.LENGTH_SHORT).show();
            }
        });

    }
}

My logcat :

08-13 22:13:32.627: E/AndroidRuntime(9554): FATAL EXCEPTION: AsyncTask #1
08-13 22:13:32.627: E/AndroidRuntime(9554): java.lang.RuntimeException: An error occured while executing doInBackground()
08-13 22:13:32.627: E/AndroidRuntime(9554):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
08-13 22:13:32.627: E/AndroidRuntime(9554):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
08-13 22:13:32.627: E/AndroidRuntime(9554):     at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
08-13 22:13:32.627: E/AndroidRuntime(9554):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
08-13 22:13:32.627: E/AndroidRuntime(9554):     at java.util.concurrent.FutureTask.run(FutureTask.java:138)
08-13 22:13:32.627: E/AndroidRuntime(9554):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
08-13 22:13:32.627: E/AndroidRuntime(9554):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
08-13 22:13:32.627: E/AndroidRuntime(9554):     at java.lang.Thread.run(Thread.java:1019)
08-13 22:13:32.627: E/AndroidRuntime(9554): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
08-13 22:13:32.627: E/AndroidRuntime(9554):     at android.os.Handler.<init>(Handler.java:121)
08-13 22:13:32.627: E/AndroidRuntime(9554):     at android.widget.Toast.<init>(Toast.java:68)
08-13 22:13:32.627: E/AndroidRuntime(9554):     at android.widget.Toast.makeText(Toast.java:231)
08-13 22:13:32.627: E/AndroidRuntime(9554):     at dev.google.imageupload.MainActivity$uploadFile.doInBackground(MainActivity.java:128)
08-13 22:13:32.627: E/AndroidRuntime(9554):     at dev.google.imageupload.MainActivity$uploadFile.doInBackground(MainActivity.java:1)
08-13 22:13:32.627: E/AndroidRuntime(9554):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
08-13 22:13:32.627: E/AndroidRuntime(9554):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
08-13 22:13:32.627: E/AndroidRuntime(9554):     ... 4 more

EDITED after zapl's suggestion :

08-13 22:38:06.297: E/AndroidRuntime(11511): FATAL EXCEPTION: AsyncTask #1
08-13 22:38:06.297: E/AndroidRuntime(11511): java.lang.RuntimeException: An error occured while executing doInBackground()
08-13 22:38:06.297: E/AndroidRuntime(11511):    at android.os.AsyncTask$3.done(AsyncTask.java:200)
08-13 22:38:06.297: E/AndroidRuntime(11511):    at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
08-13 22:38:06.297: E/AndroidRuntime(11511):    at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
08-13 22:38:06.297: E/AndroidRuntime(11511):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
08-13 22:38:06.297: E/AndroidRuntime(11511):    at java.util.concurrent.FutureTask.run(FutureTask.java:138)
08-13 22:38:06.297: E/AndroidRuntime(11511):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
08-13 22:38:06.297: E/AndroidRuntime(11511):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
08-13 22:38:06.297: E/AndroidRuntime(11511):    at java.lang.Thread.run(Thread.java:1019)
08-13 22:38:06.297: E/AndroidRuntime(11511): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
08-13 22:38:06.297: E/AndroidRuntime(11511):    at android.os.Handler.<init>(Handler.java:121)
08-13 22:38:06.297: E/AndroidRuntime(11511):    at android.widget.Toast.<init>(Toast.java:68)
08-13 22:38:06.297: E/AndroidRuntime(11511):    at android.widget.Toast.makeText(Toast.java:231)
08-13 22:38:06.297: E/AndroidRuntime(11511):    at dev.google.imageupload.MainActivity$uploadFile.doInBackground(MainActivity.java:128)
08-13 22:38:06.297: E/AndroidRuntime(11511):    at dev.google.imageupload.MainActivity$uploadFile.doInBackground(MainActivity.java:1)
08-13 22:38:06.297: E/AndroidRuntime(11511):    at android.os.AsyncTask$2.call(AsyncTask.java:185)
08-13 22:38:06.297: E/AndroidRuntime(11511):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
08-13 22:38:06.297: E/AndroidRuntime(11511):    ... 4 more
Showthrough answered 13/8, 2012 at 14:10 Comment(6)
just create the Toast directly in onPostExecute since that is already executed on the UI thread. AsyncTasks can only be executed from the UI thread and those onSomthing methods will be called from the UI thread againOvernight
Remove the runOnUiThread and that caused another problem :(Showthrough
Share the new problem :D . And also let me knw what do u want to do after your pic is uploaded.Sooth
I've edited my main post. Thanks ^^ Oh I think I can complete the rest of the project after that because I store the server response in a string that I can use later on. I just need to solve this error first :(Showthrough
Create a handler class and use that to pass into the AsyncTask and invoke the handler... You can have a constructor in the AsyncTask with the handler as parameter and from the doInBackground invoke the handler with a constant value to indicate showing a toast which will run on the UI thread - much cleaner and simpler :)Spearhead
This can also happen if one AsyncTask calls another AsyncTask.Exalt
D
59

You are attempting to update the UI from a background thread. Either move the toast to onPostExecute, which executes on the UI thread (recommended), or call runOnUiThread.

runOnUiThread(new Runnable() {
    public void run() {
        // runs on UI thread
    }
});
Dendroid answered 13/8, 2012 at 14:16 Comment(7)
Correct (which is unnecessary), but you have two Toast calls in doInBackground also, which is causing the exception.Dendroid
So you mean to say that I can't have a Toast in doInBackground? Sorry I'm kinda noob here :( sorry! EDIT I think i get it. wait a moment..Showthrough
You can, but they must be in runOnUiThread in order to be in doInBackground.Dendroid
OMG! Thank you so much (': I managed to solve the problems. By the way, I wanna know why can't I have Toast in doInBackground. I mean, while the code is running, why can't a Toast be used?Showthrough
You're welcome! Toast is a UI operation, and the UI cannot be updated directly by a background thread, which is why runOnUiThread is needed. Please mark this as the accepted answer if it solved your problem.Dendroid
Thank you so much! Sorry I'm just learning about Java! Thanks and marked!Showthrough
Thanks so much. This is the solution of my problem ;)Cairns
O
8

at dev.shaunidiot.imageupload.MainActivity$uploadFile.doInBackground(MainActivity.java:128)

You could use the progress mechanism of AsyncTasks to update UI from inside doInBackground while the task is running:

replace

Toast.makeText(getApplicationContext(), serverResponseMessage,
        Toast.LENGTH_SHORT).show();
Toast.makeText(getApplicationContext(),
        serverResponseCode.toString(), Toast.LENGTH_SHORT)
        .show();

in doInBackground with

publishProgress(serverResponseMessage, serverResponseCode.toString());

and add the following to your AsyncTask implementation

@Override
protected void onProgressUpdate(String... values) {
    if (values != null) {
        for (String value : values) {
            // shows a toast for every value we get
            Toast.makeText(MainActivity.this, value, Toast.LENGTH_SHORT).show();
        }
    }
}

You already have set String as progress type in AsyncTask<Params, Progress, Result> so in case you want to use progress for something different you can try to use runOnUiThread but I don't know if that will work.

Overnight answered 13/8, 2012 at 14:38 Comment(0)
A
0

2023, Solved this problem by calling Looper.prepare(); before creating object inside an async method.

Asafetida answered 6/3, 2023 at 4:11 Comment(1)
This removes the exception, but the Toast doesn't show when I try itBoreas

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