Error with ArrayAdapter in AsyncTask

Question

I have the following code but I get an error on this line “userSpinner.setAdapter(adapter);”

 private class Task extends AsyncTask<Void, Void, Void> 
 { 
     protected void onPreExecute() {            
     showDialog(DIALOG_TASKING); 
     } 
     protected Void doInBackground(Void... JSONArray) { 

        try
        {
        HttpGet request = new HttpGet(SERVICE_URI + "/GetBusNames");
        request.setHeader("Accept", "application/json");
        request.setHeader("Content-type", "application/json");

        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpResponse response = httpClient.execute(request);
        HttpEntity responseEntity = response.getEntity();

        char[] buffer = new char[(int)responseEntity.getContentLength()];
        InputStream stream = responseEntity.getContent();       
        InputStreamReader reader = new InputStreamReader(stream);
        reader.read(buffer);
        stream.close();

        JSONObject jsonResponse = new JSONObject(new String(buffer));
        JSONArray myUsers = jsonResponse.getJSONArray("GetBusNamesResult");

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(RealestateActivity.this, android.R.layout.simple_spinner_item);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

        adapter.add("Select a Buseness...");                
        for (int i = 0; i < myUsers.length(); ++i)
        {
            adapter.add(myUsers.getString(i));
            adapter.add(myUsers.getJSONObject(i).getString("BusName"));
        }

            userSpinner.setAdapter(adapter); // I get an error here if I wrap these two lines in /*...*/ the whole thing loads as expected but the spinner is empty
            userSpinner.setOnItemSelectedListener(new MyOnItemSelectedListener());

        }
        catch (Exception e) 
        {       
            e.printStackTrace();
            displayExceptionMessage(e.getMessage());
        }
        return null;
    }

    protected void onPostExecute(Void unused) {
        dismissDialog(DIALOG_TASKING);              
    }

}

The following is the Stack Trace produced,

11-07 19:54:35.300: ERROR/AndroidRuntime(8741): FATAL EXCEPTION: AsyncTask #1
11-07 19:54:35.300: ERROR/AndroidRuntime(8741): java.lang.RuntimeException: An error occured while executing doInBackground()
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at java.lang.Thread.run(Thread.java:1096)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at android.os.Handler.<init>(Handler.java:121)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at android.widget.Toast.<init>(Toast.java:68)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at android.widget.Toast.makeText(Toast.java:231)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at com.fnesse.realestate.RealestateActivity.displayExceptionMessage(RealestateActivity.java:271)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at com.fnesse.realestate.RealestateActivity$Task.doInBackground(RealestateActivity.java:131)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at com.fnesse.realestate.RealestateActivity$Task.doInBackground(RealestateActivity.java:1)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
11-07 19:54:35.300: ERROR/AndroidRuntime(8741):     ... 4 more
11-07 19:56:22.714: ERROR/PowerManagerService(2464): CurLock p:3 mPS:1
11-07 20:06:26.577: ERROR/libnetutils(2464): dhcp start cmd 11 : [dhcpcd:-ABK] 
11-07 20:06:27.054: ERROR/HierarchicalStateMachine(2464): TetherMaster - unhandledMessage: msg.what=3

The code works in its own method but not in the AsyncTask.

Any idea’s.

Cheers,

Mike.

Paresh Mayani · Accepted Answer · 2011-11-07T12:49:25.430

You can't perform Display/Update UI inside the doInBackground() method, instead either you can perform by implement runOnUIThread() method or write display/Update statement inside the onPostExecute() method.

In your case, write below statement inside the onPostExecute() and declare JSONArray myUsers at class level:

ArrayAdapter<String> adapter = new ArrayAdapter<String>(RealestateActivity.this, android.R.layout.simple_spinner_item);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

        adapter.add("Select a Buseness...");                
        for (int i = 0; i < myUsers.length(); ++i)
        {
            adapter.add(myUsers.getString(i));
            adapter.add(myUsers.getJSONObject(i).getString("BusName"));
        }

            userSpinner.setAdapter(adapter); // I get an error here if I wrap these two lines in /*...*/ the whole thing loads as expected but the spinner is empty
            userSpinner.setOnItemSelectedListener(new MyOnItemSelectedListener());

        }
        catch (Exception e) 
        {       
            e.printStackTrace();
            displayExceptionMessage(e.getMessage());
        }

Final Solution:

private class Task extends AsyncTask<Void, Void, Void> 
 { 
    JSONArray myUsers = null;
    JSONObject jsonResponse = null;  // this is also needed at class level

     protected void onPreExecute() {            
         showDialog(DIALOG_TASKING); 
     } 
     protected Void doInBackground(Void... JSONArray) { 

        try
        {
        HttpGet request = new HttpGet(SERVICE_URI + "/GetBusNames");
        request.setHeader("Accept", "application/json");
        request.setHeader("Content-type", "application/json");

        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpResponse response = httpClient.execute(request);
        HttpEntity responseEntity = response.getEntity();

        char[] buffer = new char[(int)responseEntity.getContentLength()];
        InputStream stream = responseEntity.getContent();       
        InputStreamReader reader = new InputStreamReader(stream);
        reader.read(buffer);
        stream.close();

        jsonResponse = new JSONObject(new String(buffer));
        }
        catch (Exception e) 
        {       
            e.printStackTrace();
            displayExceptionMessage(e.getMessage());
        }
        return null;
    }

    protected void onPostExecute(Void unused) {
        dismissDialog(DIALOG_TASKING);    

 myUsers = jsonResponse.getJSONArray("GetBusNamesResult");

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(RealestateActivity.this, android.R.layout.simple_spinner_item);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

        adapter.add("Select a Buseness...");                
        for (int i = 0; i < myUsers.length(); ++i)
        {
            adapter.add(myUsers.getString(i));
            adapter.add(myUsers.getJSONObject(i).getString("BusName"));
        }

            userSpinner.setAdapter(adapter); // I get an error here if I wrap these two lines in /*...*/ the whole thing loads as expected but the spinner is empty
            userSpinner.setOnItemSelectedListener(new MyOnItemSelectedListener());          
    }

I’ve tried all that but I get an error if I don’t try to pass a parameter into onPostExecute, so Eclipse says I have to pass either JSONObject jsonResponse, JSONArray myUsers or String buffer as a parameter from doInBackground to onPostExecute. If I do I get no errors but it crashes when I run it, I’m guessing because doInBackground has not finished what it’s doing and trying to move to onPostExecute with no data? It wont let me use "Void unused". — , Nov 07 '11 at 12:38
@MikeClarke I am sure you dont understood AsyncTask exactly, FYI onPostExecute() executes only when doInBackground() completes their execution. — Paresh Mayani, Nov 07 '11 at 12:47
@MikeClarke You are not using your own brain. Mistake is JSONObject jsonResponse = null; requires to be declared at class-level. check update in above code. — Paresh Mayani, Nov 07 '11 at 12:50
Thanks Paresh, yes I was not using my brain, I needed to declare the variables at class level. This is the first time since Uni that I have had to deal with proper programming and not web development, I have to remember threading and all the other things that you can get away with in a real language. Proper compiled software at the end of the day is more forgiving than triyng to maintain state in wb pages! I’m having lots of fun with this. — , Nov 07 '11 at 21:35
And you were right, I was not quite sure about how AsyncTask works and my next question would have been, “does onPostExecute() automatically follow on when doInBackground has finnished” but I had sort of gathered that it must. Cheers, Mike. — , Nov 07 '11 at 21:35

score 3 · Answer 2 · answered Nov 07 '11 at 09:22

3

Use below code inside your onPostExecute method.

       userSpinner.setAdapter(adapter);  
       userSpinner.setOnItemSelectedListener(new MyOnItemSelectedListener());

Try this it may help you..

answered Nov 07 '11 at 09:22

deepa

2,496
1
26
43

score 2 · Answer 3 · answered Nov 07 '11 at 09:23

2

you need to move all the UI manipulation into postExecute method which is executed in the main app thread. Android UI is not thread safe.

answered Nov 07 '11 at 09:23

slkorolev

5,883
1
29
32

score 2 · Answer 4 · answered Nov 07 '11 at 09:23

2

Don't do UI related tasks in doInBackground(). Collect your data in doInBackground() and return i from there. Get your data as a parameter to onPostExecute() and issue your userSpinner.* calls there.

answered Nov 07 '11 at 09:23

Harald Wilhelm

6,656
11
67
85

Error with ArrayAdapter in AsyncTask

4 Answers4

Final Solution:

Linked