Exceptions when using MvxAdapter
I have the following setup: Application with two tabs. In the second tab, the ListView is bound to an ObservableCollection. The first tab has controls that cause the ViewModel for the second tab to reload the ObservableCollection. It worked well until I added a custom MvxAdapter (needed for polymorphic list items). After that, after each update, I see the following exceptions in the application output (note that the list is still reloading its values):
mvx:Warning: 42.24 Exception masked during Adapter RealNotifyDataSetChanged ArgumentException: 'jobject' must not be IntPtr.Zero.
Parameter name: jobject
at Android.Runtime.JNIEnv.CallNonvirtualVoidMethod (IntPtr jobject, IntPtr jclass, IntPtr jmethod) [0x00010] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.14-series/8e79d361/source/monodroid/src/Mono.Android/src/Runtime/JNIEnv.g.cs:866
at Android.Widget.BaseAdapter.NotifyDataSetChanged () [0x00058] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.14-series/8e79d361/source/monodroid/src/Mono.Android/platforms/android-19/src/generated/Android.Widget.BaseAdapter.cs:311
at Cirrious.MvvmCross.Binding.Droid.Views.MvxAdapter.RealNotifyDataSetChanged () [0x00000] in <filename unknown>:0
mvx:Warning: 42.24 Exception masked during Adapter RealNotifyDataSetChanged ArgumentException: 'jobject' must not be IntPtr.Zero.
Parameter name: jobject
at Android.Runtime.JNIEnv.CallNonvirtualVoidMethod (IntPtr jobject, IntPtr jclass, IntPtr jmethod) [0x00010] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.14-series/8e79d361/source/monodroid/src/Mono.Android/src/Runtime/JNIEnv.g.cs:866
at Android.Widget.BaseAdapter.NotifyDataSetChanged () [0x00058] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.14-series/8e79d361/source/monodroid/src/Mono.Android/platforms/android-19/src/generated/Android.Widget.BaseAdapter.cs:311
at Cirrious.MvvmCross.Binding.Droid.Views.MvxAdapter.RealNotifyDataSetChanged () [0x00000] in <filename unknown>:0
I wonder if anyone can help me find the reason why these exceptions are being thrown.
public override View OnCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
{
base.OnCreateView(inflater, container, savedInstanceState);
var view = this.BindingInflate(Resource.Layout.ChildPage_History, null);
listView = view.FindViewById<MvxListView> (Resource.Id.history_list);
listView.Adapter = new CustomAdapter (this.Activity, (IMvxAndroidBindingContext)BindingContext);
return view;
}
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I think the problem is caused MvxListView
by the default constructor being created MvxAdapter
. When bindings are created, by default MvxAdapter
subscribes to a collection change event for the collection to which the list is bound. However, when the parameter is MvxListView.Adapter
set to a value CustomAdapter
, the original MvxAdapter
is still subscribed to the collection. Ultimately, the original one MvxAdapter
gets garbage collected, so when the collection changes the handler is called with the located object and the specified exception is the result.
I solved the problem in my project by getting my own MvxListView
that overrides the constructor and returns the adapter, i.e. there is no need to set it in the OnCreateView:
public class MyListView : MvxListView
{
public MyListView(Context context, IAttributeSet attrs) :
base(context, attrs, new CustomAdapter(context))
{
}
}
Just change the XML format to use this class instead MvxListView
and the exceptions should stop.
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