ListView's performItemClick() causes IllegalStateException when called inside onLoadFinished()

Question

I am implementing this Two Pane UI. The list view on the left pane is populated by a loader. When a list item is clicked then right pane displays details about that item.

I want to set the first item in the left pane to be selected by default and its details to be shown in the right pane. To do so, I have tried to call performItemClick() on my list like this:

listView.performItemClick(listView,
                          ListView.SCROLLBAR_POSITION_DEFAULT,
                          listView.getItemIdAtPosition(ListView.SCROLLBAR_POSITION_DEFAULT));

I'm doing this in the onLoadFinished() method of my loader because that is the point where I can be reasonably sure that the list view has been populated. This method runs in the UI thread, so I wasn't expecting any hiccups. However I get a java.lang.IllegalStateException error.

I'd like to know why performing a click action in onLoadFinished() causes the exception whereas other calls on the list view like smoothScrollToPosition() get completed.

From other SO posts I can see that it can be done using a Handler(). But it's not clear to me why scrolling the list can be done by a direct call but clicking an item requires posting to the message queue via a Handler(). I am fairly new to Android and there are gaps in my understanding of its architecture.

Here's the full code that fails:

public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
    //Update the adapter
    mForecastAdapter.swapCursor(data);

    //If there is some item in the list that was selected before then scroll to it
    if(lastSelectedIndex != ListView.INVALID_POSITION) {
        //Restore to last scrolled position
        // Get a reference to the ListView, and attach this adapter to it.
        ListView listView = (ListView) getActivity().findViewById(R.id.listview_forecast);

        listView.smoothScrollToPosition(lastSelectedIndex);
    }

    //select the first element if two pane is supported and last state doesn't exist
    else if(!mUseTodayLayout) {

        ListView listView = (ListView) getActivity().findViewById(R.id.listview_forecast);

        listView.performItemClick(listView,
                ListView.SCROLLBAR_POSITION_DEFAULT,
                listView.getItemIdAtPosition(ListView.SCROLLBAR_POSITION_DEFAULT));

    }
}

The stack trace is pasted below:

java.lang.IllegalStateException: Can not perform this action inside of onLoadFinished
            at android.support.v4.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:1369)
            at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1383)
            at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:636)
            at android.support.v4.app.BackStackRecord.commit(BackStackRecord.java:615)
            at com.example.android.sunshine.app.MainActivity.onListItemClicked(MainActivity.java:200)
            at com.example.android.sunshine.app.ForecastFragment.onLoadFinished(ForecastFragment.java:285)
            at com.example.android.sunshine.app.ForecastFragment.onLoadFinished(ForecastFragment.java:46)
            at android.support.v4.app.LoaderManagerImpl$LoaderInfo.callOnLoadFinished(LoaderManager.java:427)
            at android.support.v4.app.LoaderManagerImpl$LoaderInfo.onLoadComplete(LoaderManager.java:395)
            at android.support.v4.content.Loader.deliverResult(Loader.java:104)
            at android.support.v4.content.CursorLoader.deliverResult(CursorLoader.java:73)
            at android.support.v4.content.CursorLoader.deliverResult(CursorLoader.java:35)
            at android.support.v4.content.AsyncTaskLoader.dispatchOnLoadComplete(AsyncTaskLoader.java:223)
            at android.support.v4.content.AsyncTaskLoader$LoadTask.onPostExecute(AsyncTaskLoader.java:61)
            at android.support.v4.content.ModernAsyncTask.finish(ModernAsyncTask.java:461)
            at android.support.v4.content.ModernAsyncTask.access$500(ModernAsyncTask.java:47)
            at android.support.v4.content.ModernAsyncTask$InternalHandler.handleMessage(ModernAsyncTask.java:474)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5257)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

Answer 1

The IllegalStateException occurs not because of calling listView.performItemClick() but because this call was ultimately causing a fragment transaction. Fragment transactions are disallowed in asynchronous callbacks like onLoadFinished(). I found some useful information here.