Question

I have the task to write a user control to display some results by using the MVVM patern.

The main application (called ApplicationVM) has two a properties UserControlViewModel and SelectedRecord. The first property contains an instance of the UserControlViewModel. In XAML I use these property to bind the UserControl to the UserControlViewModel. The DependencyProperty PageCount is for simple notifications between a display function in the view and the UserControlViewModel.

<control:UserControl DataContext="{Binding UserControlViewModel}" PageCount="{Binding DocumentPageCount}" />

Here is the implementation of the second property in the ApplicationViewModel.

public Record SelectedRecord
{
    get
    {
        return m_SelectedRecord;
    }
    set
    {
        m_SelectedRecord = value;
        OnPropertyChanged("SelectedRecord");
    }
}

Later, this property will by replaced. But what I should to do is to make a dependency between the property “SelectedRecord” and a “Record” of the “UserControlViewModel” which calls a function to generate the new content (e.g. GenerateContent()). How can I make it possible that a change of the SelectedRecord property updates the Record Property of the UserControlViewModel to genereate the new content? Or can my UserControlViewModel hear the OnPropertyChanged("SelectedRecord") to generate automaticcly new content?

Answer 1

I would use a messenger – that way your view models can be nicely decoupled.

Here’s a thread on SO talking about the one in MVVM light:

MVVM light – how to access property in other view model