Passing Property Values from Parent UserControl to Child's DependencyProperty

Question

How to pass property (SomeProperty) from ParentUserControl context to DependencyProperty (MyDProperty) of the ChildUserControl?

In XAML, it should be: <uc:ChildUserControl MyDProperty="{Binding SomeProperty}"> but, for some reason, MyDProperty never gets set with Parent.DataContext.SomeProperty.

In my case, I'm passing an Action, but that's not important. I think the issue lies in the binding.

---

ParentUserControl:

    public Action RemoveEsl1 => throw new NotImplementedException();

---

    <uc:ChildUserControl Title="ESL 1" RemoveEslAction="{Binding RemoveEsl1}" DataContext="{Binding Esl1}"/>

---

ChildUserControl:

    public static readonly DependencyProperty RemoveEslActionProperty =
        DependencyProperty.Register(nameof(RemoveEslAction), typeof(Action), typeof(ChildUserControl), new PropertyMetadata(delegate { }));


    public Action RemoveEslAction
    {
        get => (Action)GetValue(RemoveEslActionProperty);
        set => SetValue(RemoveEslActionProperty, value);
    }

I found various tips here, but none of them either suited me or worked.

Answer 1

Answering my own question (check ParentUserControl):

Models:

public class RootModel : ViewModelBase
{
    private ParentModel parentModel = new();
    public ParentModel ParentModel { get => parentModel; set => RisePropertyChanged(ref parentModel, value); }
}

public class ParentModel : ViewModelBase
{
    private ChildModel childModel = new();
    public ChildModel ChildModel { get => childModel; set => RisePropertyChanged(ref childModel, value); }

    public string ParentModelProperty => "Correct value from ParentModel";
}

public class ChildModel : ViewModelBase
{
    private string childModelProperty = "Wrong default value from ChildModel";
    public string ChildModelProperty { get => childModelProperty; set => RisePropertyChanged(ref childModelProperty, value); }
}

MainWindow:

<Window.DataContext>
    <model:RootModel/>
</Window.DataContext>

<uc:ParentUserControl DataContext="{Binding ParentModel}"/>

ParentUserControl:

<uc:ChildUserControl ChildDependency="{Binding DataContext.ParentModelProperty, RelativeSource={RelativeSource AncestorType=UserControl}}" DataContext="{Binding ChildModel}"/>

ChildUserControl:

<StackPanel>
    <Label Content="Dependency property:"/>
    <Label Content="{Binding ChildDependency, RelativeSource={RelativeSource AncestorType=UserControl}}"/>
    <Separator/>
    <Label Content="Property:"/>
    <Label Content="{Binding ChildModelProperty}"/>
</StackPanel>


public partial class ChildUserControl : UserControl
{
    public static readonly DependencyProperty ChildDependencyProperty =
        DependencyProperty.Register(nameof(ChildDependency), typeof(string), typeof(ChildUserControl), new ("Wrong default DP value from ChildUserControl"));

    public string ChildDependency
    {
        get => (string)GetValue(ChildDependencyProperty);
        set => SetValue(ChildDependencyProperty, value);
    }

    public ChildUserControl()
    {
        InitializeComponent();
    }
}

So this is how to pass a property (ParentModelProperty) from ParentUserControl context to DependencyProperty (ChildDependency) of the ChildUserControl.