VB.NET WPF and Controling controls on different windows

I'm new to WPF and I'm struggling with some basic databinding and window sharing concepts.  In windows forms, controlling objects on other windows was easy.  In WPF, I can't seem to get it to work.

For example, I have three windwos at the moment:

1. MainWindow
2. LoginStart
3. ControlPanel

MainWindow is mostly what I'm using for the background and to display messages.  I have a label in the upper right hand corner for messages, called "lblInfo".  I also have a button in the lower right that is labeled "Login" - clicking this opens LoginStart.

LoginStart is a 12 button form, with a textbox for logging in.  The buttons are numbered like a keypad, with CLR and GO at the bottom.  CLR erases what's in the textbox, and GO submits the information for processing.

LoginStart is a transparent window, so the buttons just appear as if they are part of MainWindow.  When someone logs in, I want the name of the person to appear in lblInfo on MainWindow.

I thought I'd accomplish this in loginStart.xaml.vb using:
mw = new MainWindow
mw.lblInfo.Content  = FirstName & " " & LastName & " is now logged in."

Open in new window


I don't have any errors when I run this, it just doesn't do anything.

I've read tutorials and watched youtube videos on databinding, and it seems like that's the answer, but it also seems like all the suggestions I've read are much more complex than they need to be.  They're also in C#, which I'm learning, but not totally comfortable with.

So in short, my question is, what do I need to do to access controls on other windows using WPF?

Thanks for your help!!!
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slightlyoffAsked:
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MikeTooleCommented:
The short reason:
You have created an instance of MainWindow in code and set a property - but you can't see any result because, as yet, there has been no request to Show the window.
If MainWindow already on display, then that is another instance, created in some other manner, and your code doesn't refer to it.

There are many ways to address the requirement.

One is for the main window to open the login window as dialog when the login button is clicked. The main window can then retrieve data from Login, or pass a reference to itself to the login window before calling ShowDialog.

Another is to code the Login window as a UserControl rather than a Window and include that in the xaml for the main window,  binding the visibility of the control to an IsLoggedOn Boolean property (via a ValueConverter).

My advice is to search the net for articles on the MVVM approach to application structure and follow that - there may be a learning curve at the beginning, but it's worth it.
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slightlyoffAuthor Commented:
Thanks Mike,

I think you're right.  I'm working on learning MVVM.  Thanks for the help!
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