android - ListView in widget adds randomly items on scrolling and resizing (nested remoteviews)

Question

Update: I created a repository with less code to make it a bit easier to understand.

I'm trying to create a widget. I made it like described here: https://stackoverflow.com/a/6093753/2180161

It works partially, but I have a really strange bug. I made a screencast, so it's easier to understand what I mean: http://c.maysi.de/c6H9

Screenshot:

As you can see there are some items which were added randomly. (RemoteViews which were added to another RemoteViews object) The same happens when I resize the widget.

The things I printed out in the log are like expected. there is no wrong data. Also there are no new log entries when I scroll.

This is my code:

RemoteViewsFactory:

@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public class MyWidgetViewsFactory implements RemoteViewsService.RemoteViewsFactory {
    private static ArrayList<Item> items = new ArrayList<>();
    private static int itemnr = 0;
    private static int subitemnr = 0;
    private int appWidgetId;
    private Context context;

    public MyWidgetViewsFactory(Context context, Intent intent) {
        this.context = context;
        appWidgetId = intent.getIntExtra(AppWidgetManager.EXTRA_APPWIDGET_ID,
                AppWidgetManager.INVALID_APPWIDGET_ID);


        //Some random data to display
        for (int i = 0; i < 10; i++) {
            Item item = new Item(String.valueOf(itemnr++));

            for (int j = 0; j < 3; j++) {
                String[] subitem = {String.valueOf(subitemnr++), String.valueOf(subitemnr++), String.valueOf(subitemnr++)};
                item.addSubitem(subitem);
            }

            items.add(item);
        }
    }

    @Override
    public void onCreate() {
        // no-op
    }

    @Override
    public void onDestroy() {
        // no-op
    }

    @Override
    public int getCount() {
        return items.size();
    }

    @Override
    public RemoteViews getViewAt(int position) {
        Log.d("MyWidgetViewsFactory", "getViewAt(" + position + "):" + items.get(position));
        Item item = items.get(position);

        RemoteViews itemView = new RemoteViews(context.getPackageName(), R.layout.widget_listview_item);

        itemView.setTextViewText(R.id.textView_itemnr, item.getItemNr());

        for (String[] s : item.getSubitems()) {
            Log.d("MyWidgetViewsFactory", "subitem:" + s[0] + "|" + s[1] + "|" + s[2]);
            RemoteViews subitem = new RemoteViews(context.getPackageName(), R.layout.widget_listview_subitem);

            subitem.setTextViewText(R.id.textView_1, s[0]);
            subitem.setTextViewText(R.id.textView_2, s[1]);
            subitem.setTextViewText(R.id.textView_3, s[2]);

            itemView.addView(R.id.linearLayout_item_body, subitem);
        }
        return itemView;
    }

    @Override
    public RemoteViews getLoadingView() {
        return (null);
    }

    @Override
    public int getViewTypeCount() {
        return (1);
    }

    @Override
    public long getItemId(int position) {
        return (position);
    }

    @Override
    public boolean hasStableIds() {
        return (true);
    }

    @Override
    public void onDataSetChanged() {
        // no-op
    }

    class Item {
        private ArrayList<String[]> subitems = new ArrayList<>();
        private String itemnr = "";

        Item(String itemnr) {
            this.itemnr = itemnr;
        }

        Item() {
        }

        public void addSubitem(String[] subitem) {
            this.subitems.add(subitem);
        }

        public ArrayList<String[]> getSubitems() {
            return subitems;
        }

        public String getItemNr() {
            return itemnr;
        }

        public void setItemNr(String itemnr) {
            this.itemnr = itemnr;
        }
    }
}

AppWidgetProvider

    public class MyWidgetProvider extends AppWidgetProvider {

    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    @Override
    public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
        // There may be multiple widgets active, so update all of them
        Log.d("MyWidgetProvider", "appWidgetIds.lenght:" + appWidgetIds.length);
        for (int appWidgetId : appWidgetIds) {
            Intent svcIntent = new Intent(context, MyWidgetService.class);
            svcIntent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, appWidgetId);

            RemoteViews widget = new RemoteViews(context.getPackageName(), R.layout.widget_root);

            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH)
                widget.setRemoteAdapter(R.id.listView_widget, svcIntent);
            else
                widget.setRemoteAdapter(appWidgetId, R.id.listView_widget, svcIntent);

            /*
            Intent clickIntent = new Intent(context, MainActivity.class);
            PendingIntent clickPI = PendingIntent.getActivity(context, 0, clickIntent, PendingIntent.FLAG_UPDATE_CURRENT);
            widget.setPendingIntentTemplate(R.id.listView_widget, clickPI);*/

            appWidgetManager.updateAppWidget(appWidgetId, widget);
        }
    }

    @Override
    public void onEnabled(Context context) {
        // Enter relevant functionality for when the first widget is created
    }

    @Override
    public void onDisabled(Context context) {
        // Enter relevant functionality for when the last widget is disabled
    }
}

RemoteViewsService

@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public class MyWidgetService extends RemoteViewsService {
    @Override
    public RemoteViewsFactory onGetViewFactory(Intent intent) {
        return (new MyWidgetViewsFactory(this.getApplicationContext(), intent));
    }
}

---

all other resources can you find in the repo at GitHub.

---

Logcat output:

08-08 02:11:10.858  32427-32444/? D/MyWidgetViewsFactory﹕ getViewAt(0):de.mayerhofersimon.listviewproblem.MyWidgetViewsFactory$Item@3e7179c9
08-08 02:11:10.860  32427-32444/? D/MyWidgetViewsFactory﹕ subitem:0|1|2
08-08 02:11:10.864  32427-32444/? D/MyWidgetViewsFactory﹕ subitem:3|4|5
08-08 02:11:10.866  32427-32444/? D/MyWidgetViewsFactory﹕ subitem:6|7|8
08-08 02:11:10.927  32427-32443/? D/MyWidgetViewsFactory﹕ getViewAt(0):de.mayerhofersimon.listviewproblem.MyWidgetViewsFactory$Item@3e7179c9
08-08 02:11:10.927  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:0|1|2
08-08 02:11:10.927  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:3|4|5
08-08 02:11:10.927  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:6|7|8
08-08 02:11:10.931  32427-32443/? D/MyWidgetViewsFactory﹕ getViewAt(1):de.mayerhofersimon.listviewproblem.MyWidgetViewsFactory$Item@23e248ce
08-08 02:11:10.931  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:9|10|11
08-08 02:11:10.931  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:12|13|14
08-08 02:11:10.931  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:15|16|17
08-08 02:11:10.933  32427-32443/? D/MyWidgetViewsFactory﹕ getViewAt(2):de.mayerhofersimon.listviewproblem.MyWidgetViewsFactory$Item@16dbf3ef
08-08 02:11:10.933  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:18|19|20
08-08 02:11:10.933  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:21|22|23
08-08 02:11:10.933  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:24|25|26
08-08 02:11:10.936  32427-32443/? D/MyWidgetViewsFactory﹕ getViewAt(3):de.mayerhofersimon.listviewproblem.MyWidgetViewsFactory$Item@19d3defc
08-08 02:11:10.936  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:27|28|29
08-08 02:11:10.936  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:30|31|32
08-08 02:11:10.936  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:33|34|35
08-08 02:11:10.938  32427-32443/? D/MyWidgetViewsFactory﹕ getViewAt(4):de.mayerhofersimon.listviewproblem.MyWidgetViewsFactory$Item@ee985
08-08 02:11:10.938  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:36|37|38
08-08 02:11:10.938  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:39|40|41
08-08 02:11:10.938  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:42|43|44
08-08 02:11:10.941  32427-32443/? D/MyWidgetViewsFactory﹕ getViewAt(8):de.mayerhofersimon.listviewproblem.MyWidgetViewsFactory$Item@335e23da
08-08 02:11:10.941  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:72|73|74
08-08 02:11:10.941  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:75|76|77
08-08 02:11:10.941  32427-32443/? D/MyWidgetViewsFactory﹕ subitem:78|79|80
08-08 02:11:10.943  32427-32447/? D/MyWidgetViewsFactory﹕ getViewAt(9):de.mayerhofersimon.listviewproblem.MyWidgetViewsFactory$Item@229de00b
08-08 02:11:10.943  32427-32447/? D/MyWidgetViewsFactory﹕ subitem:81|82|83
08-08 02:11:10.943  32427-32447/? D/MyWidgetViewsFactory﹕ subitem:84|85|86
08-08 02:11:10.943  32427-32447/? D/MyWidgetViewsFactory﹕ subitem:87|88|89
08-08 02:11:10.945  32427-32444/? D/MyWidgetViewsFactory﹕ getViewAt(5):de.mayerhofersimon.listviewproblem.MyWidgetViewsFactory$Item@2afdeee8
08-08 02:11:10.945  32427-32444/? D/MyWidgetViewsFactory﹕ subitem:45|46|47
08-08 02:11:10.945  32427-32444/? D/MyWidgetViewsFactory﹕ subitem:48|49|50
08-08 02:11:10.945  32427-32444/? D/MyWidgetViewsFactory﹕ subitem:51|52|53
08-08 02:11:10.948  32427-32444/? D/MyWidgetViewsFactory﹕ getViewAt(7):de.mayerhofersimon.listviewproblem.MyWidgetViewsFactory$Item@1c599901
08-08 02:11:10.948  32427-32444/? D/MyWidgetViewsFactory﹕ subitem:63|64|65
08-08 02:11:10.948  32427-32444/? D/MyWidgetViewsFactory﹕ subitem:66|67|68
08-08 02:11:10.948  32427-32444/? D/MyWidgetViewsFactory﹕ subitem:69|70|71
08-08 02:11:10.951  32427-32447/? D/MyWidgetViewsFactory﹕ getViewAt(6):de.mayerhofersimon.listviewproblem.MyWidgetViewsFactory$Item@368aa3a6
08-08 02:11:10.951  32427-32447/? D/MyWidgetViewsFactory﹕ subitem:54|55|56
08-08 02:11:10.951  32427-32447/? D/MyWidgetViewsFactory﹕ subitem:57|58|59
08-08 02:11:10.951  32427-32447/? D/MyWidgetViewsFactory﹕ subitem:60|61|62

So the data gets passed correct. it just doesn't get correct displayed...

BTW: this is what it should look like: http://c.maysi.de/cB8K

Could it be, that the problem is because of nested remoteviews? because all the outer remoteviews are displayed correct...

Answer 1

Your thought behind ListView recycling issue is correct. You need to understand how things works at ground level.

MVC Pattern

The Android graphics works on the MVC pattern i.e. Model-View and Controller pattern. Model is your data, database in your case, View is your layout or graphical portion,such as ListView or RecyclerView or RemoteView. Controller changes your view after data update, parent View or ViewGroup in your case the RemoteViewsService.RemoteViewsFactory is the controller. I suggest to read further by googling the MVC model.

How Pattern is Implemented?

Any time the data changes, the view should be updated by the controller. The Android framework gives you opportunity to display your view at the given position with your data by overriding the getViewAt(int position).The controller calls the getViewAt(int position) to get the view at the given position in the ListView or RecyclerView. ListView or RecyclerView renders only visible rows on the screen. For example, If you have 100 items in the ListView and only 7 is visible on the screen than it will call getItemAt(int) 7 times. Every time you scroll the getItemAt(int) is called for the visible rows. The ListView and RemoteView take liberty to recycle/reuse the previously passed View returned by the getItemAt(int position). It ensures that memory consumed by graphical portion of your application is limited

Why there is strange behavior?

First of all every visible thing on the screen is a View such as TextView, ImageView and ListView etc. If not it can not be displayed on the screen. RemoteView is not a View. You pass the layout and data to be displayed with the RemoteView (View + Data).

Here the I am referring to your Screencast for the explanation.

1) Initialization: The ListView in your case, initially creates say 6 rows based on the visible space on screen and getViewAt(int position) is called once if getCount() returns 1. I request to check the return value of the getCount() of the List adapter.
2) You scrolled down: Nothing happens to the ListView and rendering of new Rows.
3) You Scrolled Up: getPositionAt(int position) is called again and RemoteView is passed back.Two rows are visible now. I request to check the getCount() return value. It should be 2 if not than the reason could be caching of rows by ListView.
4) You scrolled down: Nothing happens to the ListView and rendering of new Rows.
5) You Scrolled Up: Refer 3. The getCount() should be 3 and so on.

What you should do?

As per your implementation, you created the RemoteView only once and tried reusing the same view at the getItemAt(int) , may be to save on the layout inflation time.
To fix the issue, you MUST provide the FRESH RemoteView every time getItemAt(int) is called.

@Override
public RemoteViews getViewAt(int position) 
{
    Log.d("VplanWidgetViewsFactory", "getViewAt("+position+"):"+stunden.get(position));
    //TODO: Store context when constructor is called.
    RemoteView rv = new RemoteViews(context.getPackageName(), R.layout.fragment_stunde_widget);
    rv.setTextViewText(R.id.textView_lesson_nr, "" + (position + 1) + "."); <=  I have not tested this.

    return rv;
    //return stunden.get(position); <=COMMENT THIS
}