Question

I have a DataGrid and two ListBoxes in my window. I am using Entity Framework to Connect to my SQL Server. Depending on the selections I make in the ListBoxes parameters will be passed to my stored procedure and data for my DataGrid will be retrieved. I was able to implement this functionality without using MVVM. I would like to know ways to implement this using MVVM. Please Help me out. Thanks in Advance.

Answer 1

First of all, MVVM is about separating the concerns of your code into the appropriate area. For example, talking to your database via EF should be done in the Model¹. The ViewModel is responsible for holding the data, and for shaping or massaging it to make it more suitable for display (i.e. transforming enums to colors², etc).

To implement your functionality in a MVVM way, you will need to use binding, and bind your viewmodel to your view:

<MyControl>
    <LayoutRoot>
        <ListBox ItemsSource={Binding MyItems} SelectedItem={Binding MySelection} />
    </LayoutRoot>
</MyControl>

in the code behind for the View:

public class MyControl
{
    public MyControl()
    {
        this.DataContext = new MyViewModel();
    }
}

and your ViewModel will look something like this:

public class MyViewModel : INotifyPropertyChanged
{
    public ObservableCollection<MyDataObject> MyItems 
    { 
        get { return _myItems; }
        set
        {
            _myItems = value;
            OnPropertyChanged("MyItems");
        } 
    }

    public MyDataObject MySelection { get; set; }

    public void DoSomethingWithDatabase()
    {
        Model.DoSomething(MySelection);
    }
}

This is just a VERY simple example to illustrate what is required if you do things the MVVM way (and I’ve deliberately missed out a bunch of stuff). To do a proper example and document all the essential bits you need to know would take at least a chapter in a book, so I’ll refer you to a MSDN article for further reading: Implementing the Model-View-ViewModel Pattern.

¹ And the Model may just be a stepping stone if you also implement SOA, the Model might just call a service which then talks to the database.
² This can also be done with Converters in the View, but may not always be possible or practical in a converter.