Question

C#, Mono for Android. I need to output a large portion of combined data into ListView. To achieve this, I use the following obvious approach with Adapter:

class ItemInfo
{
    public string Id;
    public string Name;
    public string Description;
    public int Distance;

    //Some more data
}


class ItemAdapter : ArrayAdapter<ItemInfo>
{
    public WorldItemAdapter (Context context, int textViewResourceId, List<WorldItemInfo> items) :
    base(context, textViewResourceId, items)
    {   
    }

    //...

    public override View GetView (int position, View convertView, ViewGroup parent)
    {
        //Some stuff to format ListViewItem
    }
}


public class OutputActivity : Activity
{
    ListView _listView;

    //...

    void FillList (object SomeParameters)
    {
        var adaptedList = someDataSource.Where().Join().Union().//anything can be imagined
        .Select ((item, item2, item3) => 
            new ItemInfo (){                
                Id = item.Id,
                Name = item.Name,
                Description = String.Format(..., item2, item3),                 
                Distance = ...,
                //so on             
            }
            ).OrderBy ((arg) => arg.Name).ToList ();

        _listView.Adapter = new ItemAdapter (this, Resource.Layout.ListItemFormat, adaptedList  ());

    }
}

This works very fine… until I start to refresh my ListView frequently. If I generate many ItemInfo’s (by refreshing my view, for example), I reach GREF limit soon (described here, “Unexpected NullReferenceExceptions” section), and my application crashes. Looking into Android log, I can see thousands of Android.Runtime.IJavaObject objects, which overflow GREF limit.

According to concepts of Mono VM + Dalvik VM bridge I can understand, that my ItemInfo’s need to be passed to Dalvik VM, wrapped to IJavaObject and to be formatted in ListView by native environment – this creates GREF’s. As long as garbage collecting is a non-determined process, if I call FillList() many times, old, already used ItemInfo’s stay into memory, leaking.

How can I avoid leaking? Or, possible, is there another way to output large portions of formatted data into ListView? I tried:

• I can’t reduce the number of ItemInfo’s, as long as I need to place my data somehow.
• I can’t follow this advice, as long as my ItemInfo is not an IJavaObject.
• As a temporarily solution, I call GC.Collect() every time I need to refresh list, but this looks not a clean way. Also, if I need to output more than 2к objects into list, this doesn’t help.

Answer 1

Answer found. I’ve inherited my ItemInfo class from Java.Lang.Object explicitly and now can call Dispose() when object is no longer needed. This kills leaking GREFs.