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John Doe (Community Member)

Posted: 2 days ago | Last Reply: 1 day ago

Hi everyone,

I'm relatively new to WPF and MVVM, and I'm struggling with setting up the data binding between my main window and its corresponding ViewModel. I've created a simple ViewModel with a few properties, but I can't seem to get the binding to work. I've tried setting the DataContext in XAML and in code-behind, but the UI elements aren't updating, nor are they reflecting the initial values from the ViewModel.

Here's a simplified example of my setup:

MainWindow.xaml:


// MainWindow.xaml

MainWindowViewModel.cs:


// MainWindowViewModel.cs
using System.ComponentModel;

namespace MyWpfApp
{
    public class MainWindowViewModel : INotifyPropertyChanged
    {
        private string _windowTitle = "Default Title";
        public string WindowTitle
        {
            get { return _windowTitle; }
            set
            {
                _windowTitle = value;
                OnPropertyChanged(nameof(WindowTitle));
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

And in my MainWindow.xaml.cs constructor:


// MainWindow.xaml.cs
public MainWindow()
{
    InitializeComponent();
    DataContext = new MainWindowViewModel();
}

What am I missing? Is there a common pitfall I should be aware of?

S

Sarah Lee (WPF Guru)

Posted: 2 days ago

Hi John,

Your setup looks mostly correct. The common mistake is often with how INotifyPropertyChanged is implemented or how the DataContext is set. A few things to check:

Ensure InitializeComponent() is called before you set the DataContext. Your code-behind snippet does this correctly.
Double-check that your ViewModel class (MainWindowViewModel) is correctly referenced in your XAML (e.g., using `xmlns:local`). If you set DataContext in code-behind, this isn't strictly necessary for the binding itself, but it's good practice for design-time support.
Make sure the property name in your XAML (WindowTitle) exactly matches the property name in your ViewModel, including casing.
Is it possible that the MainWindowViewModel is throwing an exception during instantiation? Check your output window for any errors.

One way to make sure the DataContext is correctly applied is to set it in XAML:


// MainWindow.xaml (with DataContext set in XAML)

This way, the ViewModel is instantiated and set as the DataContext when the window resources are loaded. If you use this approach, you can remove the DataContext = new MainWindowViewModel(); line from your code-behind.

Let me know if that helps!

J

John Doe (Community Member)

Posted: 1 day ago

Sarah, thank you so much! I tried setting the DataContext in XAML as you suggested, and it worked immediately. It seems I had a subtle issue with the order of operations in my code-behind, or perhaps the XAML approach is just more robust for initial setup.

I've also reviewed my INotifyPropertyChanged implementation, and it appears correct. The property name casing was spot on too. It was definitely the DataContext setup.

Appreciate the clear explanation and the alternative XAML method!

How to correctly bind a ViewModel to a WPF Window?

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