In winui 3, how to bind to a dependency property of my UserControl, inside a DataTemplate of a contained ItemsControl?

Question

So I have a UserControl, which contains an ItemsControl. I need the controls defined inside the DataTemplate to bind to a dependency property in my UserControl.

Let's say my UserControl has a dependency property MyProp. I want to do the following in my xaml code...

<UserControl>
  ...
   <ItemsControl>
      <ItemsControl.ItemTemplate>
        <DataTemplate x:DataType="MyType">
           <custom:ControlThatExpectsMyType
              SomeProperty={x:Bind MyProp}>
           </custom:ControlThatExpectsMyType>
        </DataTemplate>
      <ItemsControl.ItemTemplate>
   </ItemsControl>
  ...
</UserControl>

The MyProp dependency property in the above snippet is not part of MyType, but of my UserControl. Both Binding and x:Bind are acceptable solutions, but none of the "old wpf ways" seem to be working in winui 3.

So, what's the proper -expected- way to do it in winui 3?

Andrew KeepCoding · Accepted Answer · 2024-09-02 00:48:14Z

0

Setting the x:Name for the UserControl should help. Then use Binding with the ElementName instead of x:Bind.

For example:

<UserControl x:Name="This" ...>
...
   <ItemsControl>
      <ItemsControl.ItemTemplate>
        <DataTemplate x:DataType="MyType">
           <custom:ControlThatExpectsMyType
              SomeProperty={Binding ElementName=This, Path=MyProp}>
           </custom:ControlThatExpectsMyType>
        </DataTemplate>
      <ItemsControl.ItemTemplate>
   </ItemsControl>
...
</UserControl>

Here is a sample code that works on my side:

using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Controls;

namespace UnpackagedDemo;

public sealed partial class UserControl1 : UserControl
{
    public UserControl1()
    {
        InitializeComponent();
        MyProperty = "Hello, World!";
    }

    public string MyProperty
    {
        get => (string)GetValue(MyPropertyProperty);
        set => SetValue(MyPropertyProperty, value);
    }

    public static readonly DependencyProperty MyPropertyProperty =
        DependencyProperty.Register(
            nameof(MyProperty),
            typeof(string),
            typeof(UserControl1),
            new PropertyMetadata(default));
}

<UserControl
    x:Class="UnpackagedDemo.UserControl1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:local="using:UnpackagedDemo"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    x:Name="This"
    mc:Ignorable="d">

    <Grid>
        <ItemsControl>
            <x:String>This text will be replaced with MyProperty.</x:String>
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding ElementName=This, Path=MyProperty}" />
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ItemsControl>
    </Grid>
</UserControl>

edited Sep 2, 2024 at 0:48

answered Sep 1, 2024 at 3:56

Andrew KeepCoding

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3 Comments

Frustrated Soul Over a year ago

A well-known solution, perfectly working in WPF. Unfortunately, it doesn't seem to be the case in winui 3.

Andrew KeepCoding Over a year ago

I confirmed it works before I posted my answer. I just added the sample code that works on my side.

YangXiaoPo-MSFT Over a year ago

@FrustratedSoul It works for generic controls and see learn.microsoft.com/en-us/answers/questions/1611265/…. For UserControl, could you please show a minimal, reproducible sample without private information?

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