Android: CalledFromWrongThreadException Thrown When Broadcast Intent Is Handled

Here is the basic life cycle of my application. It targets SDK version 8 by now, since I am still running Android 2.3.3 on my device. The application starts, onResume() is called

Solution 1:

The reason for your crash is because of the way that the MapChange library you are using is implemented. Under the hood, this library uses Timer and TimerTask implementations to delay firing the change event and reduce the number of calls your application gets to onMapChanged(). However, you can see from the docs on Timer that it runs its tasks in created threads:

Each timer has one thread on which tasks are executed sequentially. When this thread is busy running a task, runnable tasks may be subject to delays.

Since the MapChange library does nothing to ensure that callbacks are posted to your application on the main thread (a serious bug IMO, especially on Android), you have to protect the code you call as a result of this listener. You can see this in the example MyMapActivity bundled with the library, everything from that callback gets funneled through a Handler which posts the calls back to the main thread for you.

In your application, the code inside onMapPan() and subsequently showTrees() is being called on a background thread so it is not safe to manipulate the UI there. Using either a Handler or runOnUiThread() from your Activity will guarantee your code is called in the right place.

With regards to your second questions about AsyncTask, there is nothing stopping you from using it inside of any application component, not just Activity. Even though it's a "background" component, by default a Service is still running on the main thread as well, so AsyncTask is still necessary to offload long-term processing to another thread temporarily.

Solution 2:

If it's getting called on the wrong thread, then it's likely not on the UI thread. Have you tried this:

runOnUiThread(new Runnable() {
    public void run() {
        mapView.invalidate();
    }});