TextView setText() called in callbacks from wrong context

Question

I tried implementing a network service discovery and setting the name into a textView after successful registration. But I am getting an android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views. exception. My basic structure looks like this:

NsdManager.RegistrationListener mRegistrationListener;

onCreate() {
    mRegistrationListener = new NsdManager.RegistrationListener() {
        onServiceRegistered(serviceInfo) {
            TextView textView = (TextView) findViewById(R.id.nsdServiceNameText);
            textView.setText(serviceInfo.getServiceName());
        }
    }
    
    mNsdManager = (NsdManager) this.getBaseContext().getSystemService(Context.NSD_SERVICE);

    mNsdManager.registerService(
        serviceInfo,
        NsdManager.PROTOCOL_DNS_SD,
        mRegistrationListener);
}

It makes sense to me that I may be in the wrong context to edit the view but how did I get there and more importantly how do I solve this?

something moved you off the main thread. what that was, i don't know. how to fix it, link provided :) — a_local_nobody, Apr 15 '21 at 13:42

score 1 · Accepted Answer · answered Apr 15 '21 at 16:03

If you read the documentation of NsdManager here: https://developer.android.com/reference/android/net/nsd/NsdManager

It says that:

The API is asynchronous, and responses to requests from an application are on listener callbacks on a separate internal thread.

So it moves away from the UI thread which is where you should be updating your UI as pointed out in the comments as following:

runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    textView.setText(serviceInfo.getServiceName());
                }
            });

TextView setText() called in callbacks from wrong context

1 Answers1