Communicate from ViewModel to View

Question

I have a situation where I need to communicate from a ViewModel to View in case a change happens. The problem here is, the property I want to update does not have a DependencyProperty, and I have managed to get a way around to "bind (not really but..)" it from View to VM by breaking a little the MVVM pattern rules and simply adding in the code-behind an event:

(ViewModelSomething as DataContext).Password = pb.Password;

And this works. The problem is when I want to update this property on a View when a change happens in the VM. Is there even possible a such connection?

There is a similar question here: http://stackoverflow.com/questions/1483892/how-to-bind-to-a-passwordbox-in-mvvm. You probably won't like the accepted answer though... — Thomas Levesque, Feb 11 '14 at 19:55
why can a change to Password happen in a viewmodel without user interaction? — blindmeis, Feb 12 '14 at 06:32

score 2 · Answer 1 · answered Feb 12 '14 at 04:50

You can create a GetCredential() method in your Login View and you can get the updated values from this method in your ViewModel.

Implementation will be like

View.cs

public Credential GetCredential()
    {
        var credential = new Credential()
        {
            Username = txtUserName.Text,
            Password = txtPassword.Password
        };
        return credential;
    }

You need a Credential class

 public class Credential
    {
        public string Username { get; set; }
        public string Password { get; set; }
    }

ViewModel.cs

On Submit button Command Handler you can get values from your View

 Credential credential = View.GetCredential();

score 1 · Accepted Answer · answered Feb 11 '14 at 19:51

1

Implement INotifyPropertyChanged on the ViewModel

answered Feb 11 '14 at 19:51

Robert Levy

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That is already implemented, the problem is the Property doesn't know where to bind its value, since there is no binding in the view – jonjohnson Feb 11 '14 at 19:54
The problem is that PasswordBox.Password is not a dependency property, so it can't be bound... – Thomas Levesque Feb 11 '14 at 19:55
I know that it can't be bound or else I would just use the standard binding... I'm asking if there is a way around. – jonjohnson Feb 11 '14 at 20:07

Communicate from ViewModel to View

2 Answers2