How to access original activity's views from spawned background service

Question

I have an activity called A, and on the selection of menu item 0, it spawns service B, which starts a runnable C in a new thread. I have a TextView in activity A, which I want to access in thread C.

I've tried making the TextView a public static field, but that generates the following error:

07-21 07:26:25.723: ERROR/AndroidRuntime(1975): android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.view.ViewRoot.checkThread(ViewRoot.java:2440)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.view.ViewRoot.invalidateChild(ViewRoot.java:522)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.view.ViewRoot.invalidateChildInParent(ViewRoot.java:540)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.view.ViewGroup.invalidateChild(ViewGroup.java:2332)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.view.View.invalidate(View.java:4437)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.widget.TextView.updateAfterEdit(TextView.java:4593)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.widget.TextView.handleTextChanged(TextView.java:5932)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.widget.TextView$ChangeWatcher.onTextChanged(TextView.java:6081)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.text.SpannableStringBuilder.sendTextChange(SpannableStringBuilder.java:889)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.text.SpannableStringBuilder.change(SpannableStringBuilder.java:352)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.text.SpannableStringBuilder.change(SpannableStringBuilder.java:269)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:432)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.text.SpannableStringBuilder.append(SpannableStringBuilder.java:259)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.text.SpannableStringBuilder.append(SpannableStringBuilder.java:28)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.widget.TextView.append(TextView.java:2191)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.widget.TextView.append(TextView.java:2178)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at com.android.peekaboo.DoScan$scanBody.run(DoScan.java:36)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at java.lang.Thread.run(Thread.java:1058)

I have also considered trying to pass the View through an intent, but do not know how that would work. What do I need to make this work?

Answer 1

I was having a similar issue where a ListView was required to be updated on the web-service response coming from a separate thread.

After analyzing a similar question & example, here is a solution which should work for you:

public class A extends Activity implements Callback {

     callserviceB () { } // where your service B being called;

     @Override
     public void returnServiceResponse() {
          workOnResponse();
          handler.sendEmptyMessage(0);
     }

     private Handler handler = new Handler() {
          public void  handleMessage(Message msg) {
               //update your view from here only.
          }
     }
}

public class B implements Runnable {
     Callback callback;

     public void run() {
         //your business logic.
         callback.returnServiceResponse();
     }
}

public interface Callback {
     public void returnServiceResponse();
}