Question

I am trying to find the right way to get the data from a ChildWindow/popup using a MVVM pattern in Silverlight (3). For example: I have a main page with a data entry form and I want to open a popup with a list of customers. When user selects a customer I want to transfer selected customer into the main page. This is what the (example) code which I am using at the moment:

Main page

public partial class MainPage : UserControl
{
    public MainPageViewModel ViewModel { get; private set; }

    public MainPage()
    {
        InitializeComponent();
        ViewModel = new MainPageViewModel();
        DataContext = ViewModel;
    }

    private void SearchCustomer_Click(object sender, RoutedEventArgs e)
    {
        ViewModel.SearchCustomer();
    }
}

public class MainPageViewModel: ViewModel
{
    private string customer;
    public string Customer
    {
        get { return customer; }
        set { customer = value; RaisePropertyChanged("Customer"); }
    }

    public void SearchCustomer()
    {
        // Called from a view
        SearchWindow searchWindow = new SearchWindow();
        searchWindow.Closed += (sender, e) =>
        {
            if ((bool)searchWindow.DialogResult)
            {
                Customer = searchWindow.ViewModel.SelectedCustomer.ToString();
            }
        };
        searchWindow.Show();
    }
}

Child window

public partial class SearchWindow : ChildWindow
{
    public SearchWindowViewModel ViewModel { get; private set; }

    public SearchWindow()
    {
        InitializeComponent();
        ViewModel = new SearchWindowViewModel();
        DataContext = ViewModel;
    }

    private void OKButton_Click(object sender, RoutedEventArgs e)
    {
        DialogResult = ViewModel.OkButtonClick();
    }

    private void CancelButton_Click(object sender, RoutedEventArgs e)
    {
        DialogResult = ViewModel.CancelButtonClick();
    }
}

public class SearchWindowViewModel: ViewModel
{
    private Customer selectedCustomer;        
    private ObservableCollection<Customer> customers;

    public ObservableCollection<Customer> Customers
    {
        get { return customers; }
        set {customers = value; RaisePropertyChanged("Customers"); }
    }

    public Customer SelectedCustomer
    {
        get { return selectedCustomer; }
        set { selectedCustomer = value; RaisePropertyChanged("SelectedCustomer"); }
    }

    public SearchWindowViewModel()
    {
        Customers = new ObservableCollection<Customer>();
        ISearchService searchService = new FakeSearchService();
        foreach (Customer customer in searchService.FindCustomers("dummy"))
            Customers.Add(customer);
    }

    public bool? OkButtonClick()
    {
        if (SelectedCustomer != null)
            return true;
        else
            return null; // show some error message before that
    }

    public bool? CancelButtonClick()
    {
        return false;
    }
}

Is this the right way or is there anything more “simple”?

Cheers,
Rok

Answer 1

More problematic here is the use of View specific terms and types in your VMs. Click events, DialogResults should not be anywhere near your ViewModels.

With regards to the question, I had a similiar question about this here:
Handling Dialogs in WPF with MVVM

The answer I accepted was the use of the Mediator pattern to get around this. Have a look. 🙂