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

Question

In my new project, which I'm developing with WPF in .NET 10,

I'm having trouble using the PasswordBox in a user authentication window.

In my code, I've used the PasswordBox's KeyDown and PreviewKeyDown events.

Normally, when a user enters their password and presses Enter, if the password is correct, DialogResult is set to true and the Close() method is called.

And it's at this point that the program stops, when DialogResult is set to true.

The program crashes without returning an error message.

However, in a previous project I developed with WPF in .NET Framework,

I didn't encounter this problem. Despite my research, I haven't found a solution.

The good news is that when the validation button is clicked after entering the password, the window closes without any problem. Pressing Enter when the PasswordBox has focus causes a problem.

Please, I need to understand how to fix this bug.

Raghunath Bhukan · Answer

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 : Sets the result Calls Close() 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

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

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