Accessing UserControl's DataContext from another UserControl

Question

Given these classes:

public partial class MainPage : UserControl
{
 public MainPage()
 {
 InitializeComponent();
 //...
 }
}
public partial class LoginForm : StackPanel
{
 private LoginRegistrationWindow parentWindow;
 private LoginInfo loginInfo = new LoginInfo();
 public LoginForm()
 {
 InitializeComponent();
 //...
 }
 private void LoginOperation_Completed(LoginOperation loginOperation)
 {
 if (loginOperation.LoginSuccess)
 {
 // Here I need to access MainPages's DataContext property and set it with my ViewModel
 }
 }
}

I want to set MainPage's DataContext property inside LoginFrom. So I created the static instance of the MainPage class in the class itself:

public partial class MainPage : UserControl
{
 public static MainPage Instance { get; private set; }
 public MainPage()
 {
 InitializeComponent();
 Instance = this;
 }
}

Now I can access to the MainPage's DataContext this way:

MainPage.Instance.DataContext = new NotificationItemViewModel();

Now I'd like to hear your ideas about this kind of passing data between classes in a Silverlight application. Do you have any idea?

PS: actually I answered my original question here on Stackoverflow. But I'd like to hear your ideas in terms of code review.

Answer 1

Based on what I understood from your question here are my 5ct.

The MainPage class is the parent class of the LoginClass.

• Parents should talk to children by using methods.
• Children should talk to parents by using events.

So you should raise an event from the LoginClass to be consumed by the MainPage instead of accessing a property of the MainPage.

In this way you can easily test the code of the LoginForm independently of the MainPage whereas in you current implementation a MainPage always needs to be created before the LoginOperation_Completed() method can be used.

In addition in its current state your implementation has side effects because each time you create a new MainPage the Instance property will be changed.