ItemsControl.ItemsSource 如何从没有实现 IEnumerable 的东西绑定？

Question

ItemsControl.ItemsSource is IEnumerable . DataTable isn't IEnumerable . I would expect DataTable to fail to bind to ItemsSource . Yet, the code below works. Why?

<DataGrid ItemsSource="{Binding Table}"/>

public MainWindow()
{
    InitializeComponent();
    DataContext = this;
}

public DataTable Table { get; set; } = new DataTable();

When I set ItemsSource to DataTable without binding, it fails like I would expect. However, casting DataTable to IEnumerable<DataRowView> compiles without error.

new DataGrid().ItemsSource = new DataTable(); // Cannot implicitly convert type 'System.Data.DataTable' to 'System.Collections.IEnumerable'. An explicit conversion exists (are you missing a cast?)
new DataGrid().ItemsSource = (IEnumerable<DataRowView>)new DataTable(); // compiles without error

Does binding cast DataTable to IEnumerable<DataRowView> ? Where is the documentation for this behavior? I would expect the ItemsSource documentation to explain this casting, but I don't see anything there.

Answer 1

First of all, the cast to IEnumerable<DataRowView> does not work. It compiles, but will throw at runtime:

The binding works for DataTable because it implements IListSource

• https://docs.microsoft.com/en-us/dotnet/api/system.componentmodel.ilistsource?view=netcore-3.1

This interface is explicitly accounted for in the WPF DefaultValueConverter

• https://referencesource.microsoft.com/#PresentationFramework/src/Framework/MS/Internal/Data/DefaultValueConverter.cs,49c30fec261b0516

// special case for converting IListSource to IList
if (typeof(IListSource).IsAssignableFrom(sourceType) &&
                targetType.IsAssignableFrom(typeof(IList)))
{
    return new ListSourceConverter();
}

And the default converter is created with the binding

• https://referencesource.microsoft.com/#PresentationFramework/src/Framework/System/Windows/Data/BindingExpression.cs,444

IValueConverter converter = Engine.GetDefaultValueConverter(type, TargetProperty.PropertyType, IsReflective);