XAML x:Bind Selected Value won't bind to nullable int-CodePudding

There is some strange behavior with XAML x:Bind and attempting to bind to a nullable int:

Binding defintions:

public ObservableCollection<ListObject> List { get; set; }

public class ListObject
   {
      public int? ID { get; set; }

      public string Name { get; set; }
   }

XAML

 <ListView ItemsSource="{x:Bind ViewModel.List}"
           DisplayMemberPath="Name"
           SelectedValuePath="ID"
           SelectedValue="{x:Bind ViewModel.SelectedID, Mode=TwoWay}"/>

The following works without issue:

private int _selectedID;

public int SelectedID
   {
      get { return _selectedID; }
      set { _selectedID = value; }
   }

This does not work and is giving me an invalid object to int? casting exception:

private int? _selectedID;
    
public int? SelectedID
   {
      get { return _selectedID; }
      set { _selectedID = value; }
   }

Why does the XAML binding work on a regular int whereas the nullable int causes issues?

UPDATED

After looking into this issue a bit more it appears the g.cs file is correctly casting the int, however the cast is not generated automatically if the binding target is a nullable struct.

g.cs file for the int binding target:

private void UpdateTwoWay_25_SelectedItem()
            {
                if (this.initialized)
                {
                    if (this.dataRoot != null)
                    {
                        if (this.dataRoot.ViewModel != null)
                        {
                            this.dataRoot.ViewModel.SelectedID = (global::System.Int32)this.obj25.SelectedItem;
                        }
                    }
                }
            }

This is what the g.cs file looks like on the nullable struct:

private void UpdateTwoWay_25_SelectedItem()
            {
                if (this.initialized)
                {
                    if (this.dataRoot != null)
                    {
                        if (this.dataRoot.ViewModel != null)
                        {
                           // This line is the issue
                            this.dataRoot.ViewModel.SelectedID = this.obj25.SelectedItem;
                        }
                    }
                }
            }

Manually updating the g.cs file has the binding working correctly. I don't know if this is an issue with the new x:bind, with WinUI 3 or the Windows App SDK.

Either way, I created a bug in the Microsoft-UI-XAML git: Issue 6558

CodePudding user response：

x:Bind doesn't currently handle null values correctly. As stated in this GitHub issue from 2020, they "will look at fixing this post WinUI 3.0".