Question

Recently I’m developing my first project using MVVM concept (I use WPF). I’ve read many tutorials (ia. famous J.Smith’s one) about MVVM before I started writing a code. Everything I’ve read had been clear until I started to code…

The problem is simple: in View layer I have a form with TextBoxes. Let’s say a few TextBoxes, ie.: Name, Surname, Phone number. When user fills all of them and clicks OK-button, I want to add new person (with specified personal details) to my local Database (I use Entity Framework as a ORM).

To do this I need to write something like this:

<Button Name="MyButton" Command="MyRelayCommandWhichNeedsAllOfTheTextboxes" Content="OK" />

Using CommandParameter I can pass one object from View to ViewModel. There are many textboxes so it’s probably not a good idea.

From XAML I can assign to CommandParameter whole form which needs to be filled by user. But then, inside ViewModel, I need to know all textboxes’ names. The main assumption in MVVM is that all the layers (View, ViewModel and Model) have to be independent.

What’s the best solution? How can I pass input data from form to ViewModel?

Answer 1

I would suggest having the relay command as part of your View Model — that way, when the command gets triggered, you’ll have access to all the properties you need.

XAML:

<Button Name="SurnameTextBox" Text="{Binding Surname,Mode=TwoWay}" />
<Button Name="MyButton" Command="{Binding MyRelayCommand}" Content="OK" />

View Model:

public class MyViewModel : INotifyPropertyChanged
{
    // (note, raise property changed on the setter
    public string Surname { get; set; }

    public ICommand MyRelayCommand { get; set; }

    public MyViewModel
    {
        // set the command callback here
        MyRelayCommand = new RelayCommand(OKCommandHandler); 
    }

    private void OKCommandHandler(object parameter)
    {
        // save the record here using Surname, etc
        // (note that you don't even need to use parameter, so you can just ignore it)
    }
}