Show a modal window without blocking execution of calling code (WPF)

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Summary

The problem at hand is to show a modal window in WPF without blocking the execution of the calling code. The two usual options, Show() and ShowDialog(), do not meet the requirements. Show() continues to execute the calling code but does not prevent interaction with other windows, while ShowDialog() blocks the calling code until the new window is closed and prevents interaction with other windows.

Root Cause

The root cause of this issue is the way WPF handles window modality. When a window is shown using ShowDialog(), it is displayed as a modal window, which means that it takes focus and prevents interaction with other windows until it is closed. On the other hand, Show() displays a non-modal window, which allows interaction with other windows.

Why This Happens in Real Systems

This issue occurs in real systems because of the following reasons:

  • The need to display a progress/loading popup window that does not block the execution of the calling code
  • The requirement to prevent interaction with other windows while the popup window is visible
  • The desire to avoid disabling the main window or breaking the calling method into multiple parts

Real-World Impact

The impact of this issue is significant, as it can lead to:

  • Poor user experience due to the inability to display a modal window without blocking the calling code
  • Increased complexity in the code due to the need to break the calling method into multiple parts
  • Decreased productivity due to the time spent working around this issue

Example or Code

// Example of showing a modal window without blocking the calling code
public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private async void Button_Click(object sender, RoutedEventArgs e)
    {
        // Show the modal window
        ModalWindow modalWindow = new ModalWindow();
        modalWindow.Show();

        // Continue executing the calling code
        await Task.Delay(1000);
        Console.WriteLine("Calling code continued");
    }
}

public partial class ModalWindow : Window
{
    public ModalWindow()
    {
        InitializeComponent();
    }

    private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        // Make the window modal
        this.Topmost = true;
        this.Focus();
    }
}

How Senior Engineers Fix It

Senior engineers fix this issue by using a combination of async/await and window modality. They create a modal window that takes focus and prevents interaction with other windows, while allowing the calling code to continue executing. This is achieved by using the Show() method to display the modal window and then using async/await to continue executing the calling code.

Why Juniors Miss It

Juniors may miss this solution because they:

  • Lack experience with async/await and window modality
  • Do not fully understand the differences between Show() and ShowDialog()
  • Are not familiar with the Topmost property and its effects on window modality
  • Do not consider the user experience implications of disabling the main window or breaking the calling method into multiple parts