为什么我收到异常ViewRootImpl $ CalledFromWrongThreadException？

Question

And how should i solve it ? This is my button click method that i call it from inside onCreate:

public void addListenerOnButton()
{
    btnClick = (Button) findViewById(R.id.checkipbutton);
    btnClick.setOnClickListener(new OnClickListener()
    {
        byte[] response = null;
        @Override
        public void onClick(View arg0)
        {
            text = (TextView) findViewById(R.id.textView2);
            Thread t = new Thread(new Runnable()
            {
                @Override
                public void run()
                {
                    for (int i = 0; i < ipaddresses.length; i++)
                    {
                        try
                        {
                             response = Get(ipaddresses[i]);
                             if (response == null)
                             {
                                  text.setText("Connection Failed: " + generateRunnablePrinter(i));
                             }
                         }
                         catch (Exception e)
                         {
                              String err = e.toString();
                         }
                         if (response != null)
                         {
                             try
                             {
                                 final String a = new String(response, "UTF-8");
                                 text.post(new Runnable()
                                 {
                                     @Override
                                     public void run()
                                     {
                                         text.setText(a);
                                     }
                                 });
                                 iptouse = ipaddresses[i].substring(0, 26);
                                 connectedtoipsuccess = true;
                                 Logger.getLogger("MainActivity(inside thread)").info(a);
                             }
                             catch (UnsupportedEncodingException e)
                             {
                                 e.printStackTrace();
                                 Logger.getLogger("MainActivity(inside thread)").info("encoding exception");
                             }
                             Logger.getLogger("MainActivity(inside thread)").info("test1");
                             break;
                         }
                         else
                         {
                         }
                     }
                }
           });
           t.start();
        }
    });
}

At this place in the method inside the FOR loop the variable 'i' should be final:

text.setText("Connection Failed: " + generateRunnablePrinter(i));

But since 'i' is also the variable of the FOR loop i can't make it final. So i added the method : generateRunnablePrinter

private Runnable generateRunnablePrinter(final int value)
{
    return new Runnable() {
        public void run()
        {
            text.setText("Connection Failed: " + ipaddresses[value]);
        }
    };
}

But now using this method I'm getting the exception:

ViewRootImpl$CalledFromWrongThreadException

Answer 1

You can't change the UI "text of the TextView" from another thread so you can try AsyncTask to do the work in the background in doInBackground() method then change the UI in the method onPostExecute() .
Check out the AsyncTask: http://developer.android.com/reference/android/os/AsyncTask.html

Answer 2

Since you're adjusting your UI, you'll need to run it from the UI thread. I'd recommend this function:

runOnUiThread(new Runnable() {
    @Override
    public void run() {
    // Your code here...
    }
});

If you're calling it from anywhere else but an Activity, you'll need to either pass down the activity or get the activity using getActivity() (ie from a fragment), and then call the function from the activity, ie getActivity().runOnUiThread() { ... }