Cannot initialize window as maximized

[MartinZikmund]

Discussed in #21339

^{Originally posted by Tad29Eng August 22, 2025}
I create desktop app, how to startup main app window in maximize size (same as pressing maximize button in window)

I try use in App.xaml.cs

 var presenter = (OverlappedPresenter)MainWindow.AppWindow.Presenter;
 presenter.Maximize();

but this not worked, when app runing exception thrown: System.NullReferenceException Microsoft.UI.Windowing.OverlappedPresenter.Maximize()

[MartinZikmund]

This seems to be happening even after initialization, so this might be a deeper issue

[dgalo9]

Having the same issue, I'll appreciate any update.

[LewisIsWorking]

I have the same issue.
The closest I've been able to achieve is setting the window to use the monitor's max size, which leaves things looking strange.

[dgalo9]

@MartinZikmund any response here?? Is almost impossible to get the Host available on any part of the code. I know you should have many important things to do but this is mandatory, is making us considering to leave Uno because errors like this and not having immediate solution or not even a response is a clear red flag.

[MartinZikmund]

Unfortunately, I was focused on various client issues, which meant I wasn't able to completely fix this issue yet. That being said, it will be on my list tomorrow/beginning next week.

[dgalo9]

Thank you. I understand that paying customers are more important, and I appreciate your time. I'll continue to look for a solution so we can continue our project. @MartinZikmund

[dgalo9]

Hi @MartinZikmund This issue appears to be fixed from your side. Could you please tell me how can I apply the fix to my project?? Thanks.

[MartinZikmund]

@dgalo9 it will be included in the latest Uno.Sdk dev packages very soon (maybe today even)

[dgalo9]

@MartinZikmund thanks a lot.

[rajamatt]

Looks fixed with latest dev sdk 6.4.0-dev.34 that was released today, no more error.

---

Tested with:
Templates/SDK: 6.4.0-dev.34 (which uses Uno version 6.4.0-dev.187)
Platform(s): Desktop
IDE: VS 2022 - 17.14.16
OS: Windows