Question

I have an UserControl(AutoComplete) with his own ViewModel. When I use the UserControl inside a window, it run well, connect to a service, and paint data correctly.
The UserControl datacontext is set via xaml, and is binded to a property of the main window viewModel.

Ok, now I want that the UserControl can load data from the main window view model. The thing is that, supposing the usercontrol loads countries. When I type in the Usercontrol it returns the list of countries and when I select one of them, i.e. “Spain”, the SelectedItem property of the Usercontrols updates to “Spain”. I want an object in main window viewModel to udate to “Spain” and vice-versa, if I update the country object in the main window viewmodel, the selecteditem of the user should update too.

How can I accomplish that

I have this in my mainview:

<amctrls:AmAutoCompleteView DataContext="{Binding controladorAutoCompleteCountry}" /> 

the user control loks like this:

<telerik:RadComboBox Margin="2,0,0,0" Grid.Row="0" Grid.Column="0"  
            IsEditable="True"
            Name="RadCbo"
            ItemsSource="{Binding objectList}" 
            DisplayMemberPath="{Binding fieldToShow}"
            OpenDropDownOnFocus="True"
            SelectedItem="{Binding selectedCountry, Mode=TwoWay}"
            Text="{Binding searchText, Mode=TwoWay}"
            IsTextSearchEnabled="False" 
            StaysOpenOnEdit="True" />

controladorAutoCompleteCountry is a property of my mainview wih is an instance of the usercontrol viewmodel.

The viewmodel of the main view manage addresses, and what I want is to bind an address country to the usercontrol in order to edit the address. If i have the usercontrol binded to an instance of its controller, how can I bind the Country object of the address?

Answer 1

If you need to make those 2 views independent which is good if you want to reuse your control, go with Event Aggregator or simple events. Whenever an item is selected in the user control, it will publish an event stating, something interesting has happened. Main viewmodel can subscribe to those events and do the required. A simple case would be a creating a static class with an event and RaiseEvent method, user control will RaiseEvent and main viewmodel with be subscribing the event. Data to be passed between them can be added to the event args.