In Android, How do I change the TextView from an AsyncTask?

Question

I have a splash screen with a TextView to displays what the app is doing such as "Updating Library"... "Updating Shipping"... etc. I'm using AsyncTask to updated my database via an API.

I'm passing the update text to the AsyncTask. I need to change the text in TextView statusMessage. I'm attempting to do this:

public class JSONParser extends AsyncTask<String, String, JSONObject> {

    static InputStream is = null;
    static JSONObject json = null;
    static String outPut = "";

    TextView statusMessage;

    @Override
    protected void onPreExecute() {
        statusMessage = (TextView) findViewById(R.id.statusMessage);

    }

...

My plan is to change the text in the doInBackground method but findViewById isn't accessible in AsyncTask. I think I need to use setContentView to allow findViewById to work but I'm not sure how.

My java file is SplashScreen.java and my xml is activity_splash_screen.xml

----- EDIT -----

For more info I have three pieces talking to each other:

SplashScreen.java -> calls to method in baseActivity.java -> method sends data to JSONParser.java -> sends parsed JSON from the API to baseActivity.java to update database

Per suggestions below I've declared

statusMessage = (TextView) findViewById(R.id.statusMessage);

In baseActivity.java's onCreate since it's the file calling the AsyncTask.

In JSONParser.java I've done this, now:

public class JSONParser extends AsyncTask<String, String, JSONObject> {

    static InputStream is = null;
    static JSONObject json = null;
    static String outPut = "";

    TextView statusMessage;

    @Override
    protected JSONObject doInBackground(String... params) {
        // TODO Auto-generated method stub
    ...
    }


    protected void onProgressUpdate() {
        statusMessage.setText("testing");
     }

    protected void onPostExecute(JSONObject result) {


    }
}

I'm just using "testing" there for testing purposes.

Answer 1

My plan is to change the text in the doInBackground

Bad plan! You can't update the UI from a background Thread. You will need to do this in either onPostExecute() or onProgressUpdate().

but findViewById isn't accessible in AsyncTask.

If this is an inner class of your Activity then initialize the View in the Activity then update it in your task as described above.

If it is its own file then you will want to use an interface and have a callback to the Acitivty in onPostExecute(), onPreExecute(), or onProgressUpdate(). You can see an example of that in this SO answer.

I think I need to use setContentView to allow findViewById

Definitely! But as stated above, do this before the task such as in onCreate() of your Activity.

Edit

onProgressUpdate() takes a param but your onProgressUpdate() doesn't so it isn't the same method. That's why it complained when you had @Override which is the point of the annotation. It complains and you know you are suppose to be overriding a method so you know something is wrong with it.

Change it to

 protected void onProgressUpdate(Void...values) {
    statusMessage.setText("testing");
 }

onProgressUpdate() link

http://developer.android.com/reference/android/os/AsyncTask.html#onProgressUpdate(Progress...)

Answer 2

You should use onProgressUpdate, that method has acces to the ui thread.

public class yourAsync extends AsyncTask<> {

  @Override
  protected void onProgressUpdate() {
    textView.setText();
  }

}

Answer 3

put something like this in your activity

Handler statusUpdateHandeler = new Handler()........

In your thread, call the handler (send it a message)

MainActivity.statusUpdateHandler.sendEmptyMessage(1);

In you actual handler code, set the status message.

Answer 4

I think I need to use setContentView to allow findViewById to work but I'm not sure how.

Yes. You need to use setContentView(R.layout.activity_splash_screen) in onCreate.

You can initialize your view in onCreate make asynctask an inner class of activity and update ui in onPreExecute.

TextView statusMessage;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_splash_screen);
    statusMessage = (TextView) findViewById(R.id.statusMessage);
}

Also you can use a progressdialog and display the message. I think using progressdialog would be a better choice than textview. You can publish progress in doInbackground and update progress dialog in onProgressUpdate()

http://developer.android.com/reference/android/os/AsyncTask.html