CODEWITHSUNDEEP
androidandroid-asynctasktextview
Cypher236
Cypher236

Reputation: 527

Why isn't my textview updating?

so I have a textview which I'm trying to update from an asynctask. The message I want to update it to correctly prints to the console but for some reason it doesn't update the textview. Here are the relevant bits of code:

public class MainActivity extends AppCompatActivity{
    private MqttClient client;
    private String clientId = MqttClient.generateClientId();
    private TextView tv;
    ...

I declare the textview here, then I assign it in the onCreate() method:

tv = (TextView) findViewById(R.id.textView5);

Then in my asynctask I have this snippet which runs everytime a new message is posted to MQTT:

@Override
        public void messageArrived(String topic, MqttMessage message)
                throws Exception {
            System.out.println(message);
            if(message.toString().toLowerCase().contains(str)){
                Pattern regex = Pattern.compile("(\\d+(?:\\.\\d+)?)");
                Matcher matcher = regex.matcher(message.toString());
                while(matcher.find()){
                    System.out.println(matcher.group(1));
                    tv.setText("testing");
                }
            }
        }

The message correctly prints how I want it to the console but it doesn't update the textview and I'm not sure why.

Upvotes: 0

Views: 79

Answers (2)

Atiq
Atiq

Reputation: 14825

You should be updating your TextView in onPostExecute() of your AsyncTask.

Here is an example

protected void onPostExecute(Prams) {

    tv = (TextView) findViewById(R.id.textView5);

    tv.setText("testing");
}

Here the key point is you pass the result of your protected doInBackground(Params) to onPostExecute() and it will update your views on UiThread.

Hope it helps

Upvotes: 1

Mdlc
Mdlc

Reputation: 7288

Make sure you are calling your callback messageArrived on the UI Thread.

From a background thread, you can write to the log, but you can not update UI elements (like a textbox).

You can run code from a background task on the UI thread using runOnUIThread

    runOnUiThread(new Runnable() 
    {       
        public void run() 
        {
            // update UI code
        }
    });

In you case, that would mean moving either the call to the callback (e.g. callback.messageArrived(..)) or setting the textview (tv.setText("testing");) from the runnable

Upvotes: 1

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