Question

I have the following structure:
Window1 -> UserControlA -> UserControlB -> UserControlC

Each has its own view model. How can I create a property on UserControlA that depends on a property of UserControlC?

The only thing I can think of is to expose C’s property changed event from B so I can listen for the C’s events from A and update A’s dependency property. The problem is that this seems WAY too contrived so I think there has to be a simpler solution.

Answer 1

You can chain the Dependency Properties to achieve this. You need to expose dp in all your user controls. Bind the property of UserControlC with UserControlB and then UserControlA. This way whenever property in UserControlC is changed, property in UserControlA is also changed.

A.xaml.cs

class VewModelA : INotifyPropertyChanged
{
    prop TextA {get {return thevalue;} set : set thevalue & RaisePropertyChanged("TextA")}
}

B.xaml.cs

class ViewModelB : INotifyPropertyChanged
{
    prop TextB {get {return thevalue;} set : set thevalue & RaisePropertyChanged("TextB")}
}

C.xaml.cs

class ViewModelC : INotifyPropertyChanged
{
    prop TextC {get {return thevalue;} set : set thevalue & RaisePropertyChanged("TextC")}
}

A.xaml

<controls:B TextB={Binding TextA, Mode=TwoWay}" />

B.xaml

<controls:C TextC={Binding TextB, Mode=TwoWay}" />

Whenever Text of C is changed, binding updates the value of TextA. And definitely you have to map the dp with their corresponding viewmodel properties in their control template.