Difficulty using the PasswordBox in my WPF project in .Net 10

This is a real WPF behavior change / pitfall.

The key point is:

In WPF, setting DialogResult immediately closes the window — and doing it from certain input events (like KeyDown on PasswordBox) can crash the app if not done correctly.

What’s actually going wrong

1. DialogResult in WPF is not passive

In WPF:

DialogResult = true;

does three things at once:

1. Sets the result

2. Calls Close()

3. Ends the modal message loop (ShowDialog())

So this:

DialogResult = true;
Close();

is already dangerous (double-close).

2. Why it crashes specifically on Enter in PasswordBox

PasswordBox is special:

• It handles keyboard input internally

• Enter is processed before WPF finishes its input pipeline

• Closing the window inside KeyDown / PreviewKeyDown interrupts that pipeline

In newer .NET / WPF builds (including .NET 8+ / .NET 10):

• WPF is stricter

• This results in an unhandled dispatcher exception

• Often appears as a silent crash if not observed in the Output window

That’s why:

• ? Clicking the button works

• ? Pressing Enter crashes

3. Why it worked in .NET Framework

Older WPF versions were more forgiving:

• Re-entrancy issues were swallowed

• Input pipeline teardown was less strict

.NET Core / .NET 5+ WPF fixed (or exposed) this behavior.

? What NOT to do

private void PasswordBox_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Key == Key.Enter)
    {
        DialogResult = true; // ? closes window immediately
        Close();             // ? second close
    }
}

or even:

DialogResult = true; // ? still unsafe inside KeyDown

? Correct & SAFE solutions

? Solution 1 (BEST PRACTICE): Use a default button (IsDefault)

This is the WPF equivalent of WinForms AcceptButton.

private void Login_Click(object sender, RoutedEventArgs e)
{
    if (ValidatePassword())
    {
        DialogResult = true;
    }
}

? No KeyDown handling
? No crashes
? Native WPF behavior
? Accessible & clean

This is the recommended solution.

? Solution 2: Use Dispatcher to defer closing

If you must handle Enter manually:

private void PasswordBox_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Key == Key.Enter)
    {
        e.Handled = true;

        Dispatcher.BeginInvoke(new Action(() =>
        {
            if (ValidatePassword())
            {
                DialogResult = true;
            }
        }), DispatcherPriority.ApplicationIdle);
    }
}

Why this works:

• Lets WPF finish processing the key event

• Closes the dialog after input handling completes

? Solution 3: Don’t set DialogResult in KeyDown at all

private void PasswordBox_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Key == Key.Enter)
    {
        Login_Click(sender, e);
    }
}

Still relies on the button logic, not raw dialog manipulation.

Important rules to remember

Rule 1

Never call Close() after setting DialogResult

DialogResult = true; // already closes the window

Rule 2

Only set DialogResult on a window shown with ShowDialog()

Otherwise WPF throws internally.

Rule 3

Avoid closing windows inside low-level input events

(KeyDown, PreviewKeyDown, TextInput)
Use commands or buttons instead.

? Final recommendation

For authentication dialogs in WPF (.NET 10):

? Use PasswordBox
? Use a Login button with IsDefault="True"
? Set DialogResult only in the button click
? Do NOT handle Enter manually unless absolutely necessary