Passing value from child window to parent window using WPF and MVVM pattern

Question

I have parent window which has textBox called \"SchoolName\", and a button called \"Lookup school Name\".

That Button opens a child window with list of school names.

Answer 1

The Solution Sam suggested here is a correct one. What you didn't get is that you should have only one instance of you viewmodel and your main and child page should refer to the same one. Your viewmodel should be instanciated once: maybe you need a Locator and get the instance there... Doing like this the code in your ctor will fire once, have a look at the mvvmLight toolkit, I think it will be great for your usage, you can get rid of those Classes implementing ICommand too... You can find a great example of using that pattern here: http://blogs.msdn.com/b/kylemc/archive/2011/04/29/mvvm-pattern-for-ria-services.aspx basically what happens is this:

you have a Locator

public class ViewModelLocator 
{
    private readonly ServiceProviderBase _sp;

    public ViewModelLocator()
    {
        _sp = ServiceProviderBase.Instance;

        // 1 VM for all places that use it. Just an option
        Book = new BookViewModel(_sp.PageConductor, _sp.BookDataService); 
    }

    public BookViewModel Book { get; set; }
    //get { return new BookViewModel(_sp.PageConductor, _sp.BookDataService); }

    // 1 new instance per View 
    public CheckoutViewModel Checkout
    {
        get { return new CheckoutViewModel(_sp.PageConductor, _sp.BookDataService); }
    }
}

that Locator is a StaticResource, in App.xaml

in your views you refer you viewmodels trough the Locator:

   DataContext="{Binding Book, Source={StaticResource Locator}}"

here Book is an instance of BookViewModel, you can see it in the Locator class

BookViewModel has a SelectedBook:

 private Book _selectedBook;
        public Book SelectedBook
        {
            get { return _selectedBook; }
            set
            {
                _selectedBook = value;
                RaisePropertyChanged("SelectedBook");
            }
        }

and your child window should have the same DataContext as your MainView and work like this: