Question

I have a user control which I would like to add a dependency property of type Func so I can assign it a method handler in XAML. However, this will cause an XAMLParseException: ‘Func`2’ type does not have a public TypeConverter class. What am I doing wrong? Do I need to implement a TypeConverter for Func or is there a better way?

The Func Dependency Property in the user control (MyUserControl):

public Func<int, int> MyFunc
{
    get { return (Func<int, int>)GetValue(MyFuncProperty); }
    set { SetValue(MyFuncProperty, value); }
}

public static readonly DependencyProperty MyFuncProperty =
    DependencyProperty.Register("MyFunc", 
                                typeof(Func<int, int>), 
                                typeof(SillyCtrl), 
                                new UIPropertyMetadata(null));

Example of using the DP, XAML:

<Window x:Class="FuncTest.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:FuncTest="clr-namespace:FuncTest"
    Title="Window1" Height="300" Width="300">
    <Grid>
        <FuncTest:MyUserControl MyFunc="SquareHandler" />
    </Grid>
</Window>

Code behind:

namespace FuncTest
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();

            SquareHandler = (arg => arg * arg);

            DataContext = this;
        }

        public Func<int, int> SquareHandler { get; set; }
    }
}

Answer 1

MyFunc="SquareHandler"

Means set “MyFunc” property to a “SquareHandler” string and that’s why it asks you for a TypeConverter able to converting strings into Funcs, change it to

<FuncTest:MyUserControl MyFunc="{Binding SquareHandler}" />

to use SquareHandler property of the current DataContext.