Apply Fluent Theme to WPF MessageBox

[JackDjTom]

Since .NET 9 fluent theme is available for WPF. But the MessageBoxes still looks old.

Current MessageBox Style

Expected MessageBox Style with fluent theme (Dialog from Microsoft Paint)

[miloush]

The MessageBox is a function of the OS and not of theming. Microsoft Paint is using custom-made dialogs and if you make your own dialogs too, they too can have a theme applied.

[ThomasGoulet73]

MessageBox is just a wrapper around the Win32 control. WPF does not control the styling inside the MessageBox. You need an app mainfest to use the more modern controls (See #5967 (comment)).

[miloush]

Note @ThomasGoulet73 that manifest does not help achieving the desired outcome here.

[ThomasGoulet73]

@miloush Agreed, the message box won't be the same as Paint but it will be more modern.

[Symbai]

And is there a good reason why WPF doesn't have a modern looking dialog system with custom controls? I can understand that Winforms uses WinAPIs for that. I can understand that WPF (1.0) used that. I don't understand why WPF in 2025 still uses WinAPI for this. What's wrong with a fluent message box? The way it would be implemented (opt-in, breaking change, new public API like FluentMessagebox etc) can be discussed later. But I think the question of whether something like this should be introduced in general is quite justified.

[dipeshmsft]

@Symbai , what you are asking for, it is same as WinUI's ContentDialog or WinForm's TaskDialog API right ?

[Symbai]

I think the TaskDialog from WinForms also uses WinAPI. From screenshots its more like the ContentDialog although I have no experience with WinUI. Almost all styled WPF apps use a custom dialog / messagebox. And it shouldn't be too difficult. Its a simple WPF window which shows icons and buttons depending on how it was called. Like the existing MessageBox. But because its a WPF window it has the same style as the rest of your application.

And I don't think much more than this would be necessary for a "solution built into WPF". I wouldn't allow displaying custom content (controls). I also wouldn't make it a dialog which is centered on your app and draws a transparent shadow on its background. Instead just provide the same you can do with MessageBox already but put it into a WPF window so it has the same look as the rest. In this case: fluent.