Btukfyl

I am stuck in this problem since a few days, can't solve it :

I have some views V1, V2, ..., with view-models V1vm, V2vm,..., each using a UserControl MyUC, with view-model MyUCvm. UserControl MyUC depends on a bool attached property myParam. Let's say view V1 defines the value through a CheckBox. I can bind myParam to the CheckBox.IsChecked in V1 XAML :

<UserControl x:Class="V1" ...>

   ...

   <CheckBox x:Name="cb" />

   <MyUC local:MyUC.myParam="{Binding ElementName=cb, Path=IsChecked}" />

</UserControl>

In view-model MyUCvm I declare a property :

public class MyUCvm : ViewModelBase

{

   private bool _condition;

   public bool Condition

   {

       get { return condition; }

       set

       {

          _condition = value;

          Notify("Condition");

       }

   }

   ...

}

I want Condition to be bound to myParam so that what is displayed by MyUC in View V1 depends on the checkbox cb (and other patterns for the other views).

Maybe I could code in V1vm an update of MyUCvm in C#. But I believe this is not the right way.

It seams to me that it is more "pure" to bind myParam in MyUC XAML to Condition, with some kind of (not working) code :

<UserControl x:Class="MyUC" ...>

   ...

   <WHAT_TO_PUT_HERE? local:MyUC.myParam="{Binding Condition, Mode=TwoWay}" />

   ...

</UserControl>

Am I targeting the right solution ?
How to acheive this ?

When you need one custom control to bind to the properties of another control, you best solution is going to be to register dependency properties in the code behind of the custom control who has bound properties that need exposed.

You can certainly still get and set your viewModel bindable properties from within the get and set of your registered dependency property. However, that is going to be your best bet.

So make a DependencyProperty for your type of controller, give it a name, and register the onChanged if you care to monitor it in code. Then create your get and set properties for it to point the dependency property to.

From their, compile and reopen the xaml file that is trying to utilize it, and the property will now be there in auto-fill intellisense for you to bind to.

Happy Coding.

Actually instead of twisting everything around, I have chosen to use simple ViewModel logic, which is much simpler.

In ViewModels V1vmand V2vm I define a property of type MyUCvm that I use to define the DataContext of the <local:MyUC DataContext={Binding RefToMyUCvm} ... /> xaml element in views V1and V2.

In V1vmand V2vm I use a bool property MyParam to bind to the CheckBox.IsChecked (or something else ...). And I do the work in getter/setter of the property.

public class V1vm : ViewModelBase

{

  //...



  public MyUCvm RefToUCvm { get; set; }



  public bool MyParam

  {

     get { return MyUCvm?.MyParam ?? false; }

     set

     {

         if (MyUCvm != null)

         {

              MyUCvm.MyParam = value;

              NotifyPropertyChanged("MyParam");

         }

      }

   }

}

This is much straitforward and simple...