Question

I have the following test code (based on standard monodroid HelloWorld)

namespace TestGREF
{
    [Activity (Label = "TestGREF", MainLauncher = true)]
    public class Activity1 : Activity
    {
        int count = 1;      
        protected override void OnCreate (Bundle bundle)
        {
            base.OnCreate (bundle);
            SetContentView (Resource.Layout.Main);
            Button button = FindViewById<Button> (Resource.Id.myButton);

            button.Click += delegate {
                button.Text = string.Format ("{0} clicks!", count++); 
                for(int i=0;i<10000;i++){
                    new Java.Lang.Object(new System.IntPtr(i));
                    //...some stuff here. Instead of Java.Lang.Object may be
                    //something much more useful.
                }

                //If uncomment here, looks ok
                //GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced);
            };
        }
    }
}

If I click the button 5-6 times, application crashes.

I know this happens because of global refences (GREF) limit (described here, “Unexpected NullReferenceExceptions” section). The question is: what to do with it? What is the best practice? If possible, with code example please

If uncomment GC.Collect() call, all seems working, but calling GC too often is too exspensive for performance. Another popular design is to put new statement put of loop, but it is not always possible cause of program logic.

Any more ideas?

Answer 1

for(int i=0;i<10000;i++){
    var obj = new Java.Lang.Object(new System.IntPtr(i));

    //...some stuff here. Instead of Java.Lang.Object may be
    //something much more useful.

    obj.Dispose(); //Deletes an object and GREF too. 
    //Cannot be used if object is still used in dalvik VM
}

If you cannot use Dispose() (for example, unmanaged object is a part of layout, which will be used by android lated, but not by C# code), use GC.Collect() wisely. GC.Collect() kills all the GREFs to variables, which are out of usage by Mono Environment and out of current scope.