使用自定义类型扩展名指定DataTemplate.DataType

I have this markup extension

我有这个扩展标记

public class NullableExtension : TypeExtension
{
    public NullableExtension() {
    }

    public NullableExtension( string type )
        : base(type) {
    }

    public NullableExtension( Type type )
        : base(type) {
    }

    public override object ProvideValue( IServiceProvider serviceProvider ) {
        Type basis = (Type)base.ProvideValue( serviceProvider );
        return typeof(Nullable<>).MakeGenericType( basis );
    }
}
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