Code Behind WPF - How to access or pass UI elements into event handlers?

Question

For better or worse, I am building a WPF UI in code behind only. I have a button and a Text block within a Stack Panel. The button, upon clicking, updates the TextBlock with some information. If I make the TextBlock a member of the class, it will work successfully. However, just declaring global UI elements all over the place feels like the easy way out. Is there a way to instantiate the TextBlock in the MainWindow() and still have access to it in the button click Event?

The following pseudo code works:

public partial class MainWindow : Window
{
    public TextBlock myTextBlock;

    public MainWindow()
    {

        StackPanel mainStackPanel = new StackPanel();

        Button myButton = new Button();

        myButton.Click += NewButton_Click();

        mainStackPanel.Children.Add(myTextBlock);

        mainStackPanel.Children.Add(myButton);

        Content = mainStackPanel;

    }

    private void NewGridButton_Click(object sender, RoutedEventArgs e)
    {
        myTextBlock.Text = "Some Text"
    }

}

However, I am curious if something along these lines is also possible:

public partial class MainWindow : Window```
{
    public MainWindow()
    {

        StackPanel mainStackPanel = new StackPanel();

        Button myButton = new Button();

        TextBlock myTextBlock = New TextBlock();

        myButton.Click += NewButton_Click();

        mainStackPanel.Children.Add(myTextBlock);

        mainStackPanel.Children.Add(myButton);

        Content = mainStackPanel;

    }

    private void NewGridButton_Click(object sender, RoutedEventArgs e)
    {
        //Somehow Access the myTextBlock from MainWindow here in order to set the text?

        myTextBlock.Text = "Some Text" // This would not compile.
    }

}

For brevity, the code here is just for example and not fully functional. Thank you in advance for any information you may be able to share on this topic.

---

EDIT - Follow up. The consensus from the answers here seem to indicate I was overthinking this issue. A private class variable that represents the UI element I wish to use seems to be a universally accepted (and not necessarily a lazy) way to declare and access your UI elements. Thanks to everyone who took the time to review and comment.

Answer 1

The use of a locally scoped variable isn't a bad thing in this case (as per your original example). It may feel ugly but it is essentially what gets created in the background by defining things in a XAML file.

As an alternative, see this question/answer that contains code to locate a control as well as a reference to a VisualTreeHelper that could assist. In my opinion, though, both these options are less elegant than the original idea.

Answer 2

This is a diabolically bad misuse of WPF, and I suspect you already know that. But if you insist, you can give your TextBlock a name when you create it:

myTextBlock.Name = "MyTextBlock";

You can then traverse the visual tree at any time to find it. Add the code for FindChild in this answer to your class, then do this in your click handler:

private void MyButton_Click(object sender, RoutedEventArgs e)
{
    var textBlock = FindChild<TextBlock>(this, "MyTextBlock");
    textBlock.Text = "Hello World!";
}

If it's just the dynamic creation of child controls you need to support then a marginally better solution would be to create a dictionary for them:

private Dictionary<string, FrameworkElement> Children = new Dictionary<string, FrameworkElement>();

...to which you would then add each of your controls to, using unique identifiers:

TextBlock myTextBlock = new TextBlock();
this.Children["MyTextBlock"] = myTextBlock;

While still not the "proper" way of doing this in WPF, at least you'd no longer have to traverse the entire tree looking for the element you're after:

var textBlock = this.Children["MyTextBlock"] as TextBlock;
textBlock.Text = "Hello World!";

Answer 3

If you don't store a reference to the TextBlock in a field, you need to get a reference to it dynamically somehow.

There are various ways to do this. You may for example get in from the Children collection of the root Panel:

private void NewGridButton_Click(object sender, RoutedEventArgs e)
{
    TextBlock myTextBlock = (Content as Panel).Children.OfType<TextBlock>().FirstOrDefault();
    if (myTextBlock != null)
        myTextBlock.Text = "Some Text";
}

Or by name if you register it:

public MainWindow()
{
    ...

    TextBlock myTextBlock = new TextBlock();
    RegisterName("myTextBlock", myTextBlock);

    ...
}

private void NewGridButton_Click(object sender, RoutedEventArgs e)
{
    TextBlock myTextBlock = FindName("myTextBlock") as TextBlock;
    if (myTextBlock != null)
        myTextBlock.Text = "...";
}

Neither of these approaches are "better" than storing the reference in a field though. Using a field, you don't have to perform any dynamic lookups.

Answer 4

i think that the best way to to move the event code to a method

private void NewGridButton_Click(object sender, RoutedEventArgs e)
{

    NewGridButtonClick();

}

 private void NewGridButtonClick()
 {
    myTextBlock.Text = "Some Text" // This would not compile.
 }

then from any place in your app you may call it

 private void SomeButton_Click(object sender, RoutedEventArgs e)
{

    MainWindow.NewGridButtonClick();

}