Why does my android debugging fail permanently?

See more:

Mobile

Android

I have a little app I am trying to run on my phone as I build it, to see if things are going properly. The trouble starts in onCreate in MainActivity, which looks like this:

public class MainActivity extends ListActivity {

    public static final String TAG = "MAIN";
    public static final String WEIGHTS_DIR = "/weights/input";
    // TODO Get this dir from app settings.

    // Keeps the filename whenever a user selects a file. Used when the user taps the 'Process' buttob.
    private String selectedFileName = "";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d(TAG, "Completed 'setContentView'.");

        String topDir = Environment.getExternalStorageDirectory().getAbsolutePath() + WEIGHTS_DIR;
        List<String> input_files = FileHelper.getInputFileNames(topDir);
        Log.i(TAG, getString(input_files.size()) + " input files found.");

//        ListAdapter listAdapter = new ArrayAdapter<>(this, R.layout.list_item, R.id.files_list, input_files);
//        setListAdapter(listAdapter);
//        final ListView listView = getListView();
//        listView.setChoiceMode(ListView.CHOICE_MODE_SINGLE);
    }

Before I add the ListView code, now commented out, the app starts up on my device, and debugging works nicely, stopping at breakpoints, examining variables, etc.

As soon as I add that code, I get the following messages:

Connected to the target VM, address: 'localhost:8610', transport: 'socket'
Disconnected from the target VM, address: 'localhost:8610', transport: 'socket'

with "Disconnected" instantly after "Connected", where, when things were still nice, I would only get "Connected", and the main layout would display on the phone.

Then, on the phone, I clear the app's data and uninstall it, and comment out the ListView code, yet the debugging remains broken, with the instant "Disconnect" still there. I suspect some artefact in Android Studio's output is not being deleted when I rebuild, even after I do a clean. Once the debugging is broken like this, it also acts broken on an emulator for the phone, and a Nexus 9 emulator, so it really doesn't look device specific.

Worth noting is that if I do a Git reset on the branch I create before adding the ListView code, then debugging works again.

What I have tried:

I don't have much to try - I'm a complete Android Novice. If I copy all the code, minus the ListView stuff, into a new project, debugging works again. I have tried a breakpoint on the first line of the ListView stuff, so it doesn't execute until I want to, but the debugging still breaks as soon as I add that code. FileHelper is my own class, and getInputFileNames works fine and returns all files in the given directory.