WPF VB.NET - Reference Controls in MainWindow from a Module

Question

I want to use modules in my first WPF application, as I'm used to using them in WinForm applications I've created before. So I have this button, with a textblock inside.

MainWindow.xaml:

<Button x:Name="Connection_Button" Width="200" Height="30" Margin="5,5,5,5">
                        <TextBlock FontSize="14" MouseDown="TextBlock_MouseDown">CONNECT</TextBlock>
                    </Button>

Before in WinForms I could easily reference a button and it's text property by adding MainForm. before the control, but how can I do this in WPF through modules, similar to below? How do I even declare the controls at the top of my module code? And elements inside a control such as TextBlock?

Module_Connection.vb in my old WinForm way:

Private Sub Connect()
        If MainForm.Connection_Button.Text = "Connect" Then
        ' Code

Answer 1

You don't usually do this in WPF.

To base your application logic in the state of UI elements is not really a good idea.

Why? because UI is Not Data and therefore you should base your application logic on the state of data items instead.

I suggest you read this and this

To try to use WPF the same way you use winforms is a straight path to miserable failure and suffering.

You must embrace MVVM and understand DataBinding and how the UI must always be separate from Application Logic and Data.

Edit: Adding a Code Sample (in C#)

ViewModel:

public class MainViewModel
{
    public string ButtonContent {get;set;} //TODO: Add Property Change Notification

    public MainViewModel()
    {
        ButtonContent = "SomeButtonContent";
    }
}

View:

<Button Width="200" Height="30" Margin="5,5,5,5">
    <TextBlock FontSize="14" Text="{Binding ButtonContent}"/>
</Button>

Code Behind:

public class MainWindow: Window
{
    public MainWindow()
    {
        InitializeComponent();
        SomeModule.Instance = new MainViewModel();
        DataContext = SomeModule.Instance;
    }
}

Module (static class in C#):

public static class SomeModule
{
    public static MainViewModel Instance {get;set;}

    public void DoSomething()
    {
        if (Instance.ButtonContent == "SomeButtonContent")
            //...etc
    }
}

This is what I mean by separating the UI from the data. You place your strings in a ViewModel, not in the View, then you evaluate the value of those ViewModel properties to determine what to do.

Still, basing your application logic on the value of a string seems like a weak solution. What do you really need to do? There are much better approaches such as using an Enum for this.

Edit2:

Having a ViewModel to Bind to does not "complicate" things. It actually simplifies them a LOT.

How? because you're now doing this with simple controls, but then you'll want to do the same thing with UI elements inside a ControlTemplate or even worse a DataTemplate and that's when real problems arise.

Therefore, you must get used to "the WPF Way" before you deal with more complex UI scenarios.

Non-optimal approach:

public class MainWindow: Window
{
     public string ButtonContent
     {
         get
         {
             return this.txtButtonContent.Text;
         }
         set
         {
             this.txtButtonContent.Text = value;
         }
     }
}

<Button Width="200" Height="30" Margin="5,5,5,5">
    <TextBlock x:Name="txtButtonContent" FontSize="14" Text="Connect"/>
</Button>

You must understand that the Button class doesn't have a Text property in WPF. In contrast to most ancient framweworks, WPF has a Content Model where literally anything can contain anything with little to no restrictions. Putting a Text property to the Button would be to introduce the limitation for the Button to only contain Text, which is not the case in WPF.

Therefore, what you actually want to do here is to modify the Text property of the TextBlock (which happens to be inside the Button, but could actually be anywhere in the Visual Tree).

That's why I mentioned the fact that you actually NEED a ViewModel to hold your data, because there is no (easy) way to access the UI elements located, for example within a DataTemplate in order to manipulate them. Your UI must always be a reflection of the state of your application's Data, which is stored in Model or ViewModel classes, not the UI.

Answer 2

This should get you in the ballpark:

Module: Public Sub Connect(RyRef txtBox as TextBox) If txtBox.Text = "...

note Public vs. Private

Call: Call .Connect(MyTextBox1)

Call and are optional

Answer 3

I'll answer your question in VB.NET and not provide C# samples of alternative ways of doing it which if you're not used too can be an uphill struggle.

Declare this in your module, access the controls through rootWindow.

Private rootWindow As MainWindow = TryCast(Application.Current.MainWindow, MainWindow)

Answer 4

Another approach is :

Dim mw as MainWindow = Application.Current.Windows.OfType(Of MainWindow).First

assuming you have a MainWindow and only have one MainWindow.