[BUG] PageDialogService.DisplayAlertAsync causes ArgumentNullException in .NET 10

[kevin-dev31]

Description

When using Prism.Maui's PageDialogService.DisplayAlertAsync in .NET 10 environment, an ArgumentNullException occurs causing the application to crash. Despite passing clearly non-null string parameters, the cancel parameter is somehow converted to null within Prism's internal processing and causes an error when passed to MAUI's Page.DisplayAlertAsync.
##[+] Expected Behavior[/+][-] Steps to Reproduce[/-]
[+]Dialog should display normally and allow user to select "OK" or "Cancel"[/+][-] 1. Create a .NET 10.0.100-preview.3.25201.16 project[/-]
[-]2. Add Prism.DryIoc.Maui 9.0.537[/-]
[+]## Actual Behavior[/+][-] 3. Implement the sample code below[/-]
[+]App crashes with ArgumentNullException: Value cannot be null. (Parameter 'cancel')[/+][-] 4. Run the app on Android emulator[/-]
[-]5. Tap the "Show Dialog" button[/-]
[+]## Environment[/+][-] 6. App crashes with ArgumentNullException[/-]
[+]- .NET SDK: 10.0.100-preview.3.25201.16[/+]
[+]- Microsoft.Maui.Controls: 10.0.0-preview.3.25208.1[/+][-] ## Expected Behavior[/-]
[+]- Prism.DryIoc.Maui: 9.0.537[/+][-] Dialog should display normally and allow user to select "OK" or "Cancel"[/-]
[+]- Platform: Android[/+]
[-]## Actual Behavior[/-]
[+]## Code to Reproduce[/+][-] App crashes with ArgumentNullException: Value cannot be null. (Parameter 'cancel')[/-]
[+]### MainPageViewModel.cs[/+][-] ## Environment[/-]
[+]csharp[/+][-] - .NET SDK: 10.0.100-preview.3.25201.16[/-] [+]using Prism.Commands;[/+][-] - Microsoft.Maui.Controls: 10.0.0-preview.3.25208.1[/-] [+]using Prism.Mvvm;[/+][-] - Prism.DryIoc.Maui: 9.0.537[/-] [+]using Prism.Services;[/+][-] - Platform: Android[/-] [+]namespace PrismBugSample;[/+][-] ## Did you find any workaround?[/-] [-]No, there is no practical workaround. While it's technically possible to bypass Prism and call MAUI's DisplayAlert directly, this defeats the purpose of using Prism's abstraction and testability benefits, so it's not a viable solution.[/-] [+]public class MainPageViewModel : BindableBase[/+] [+]{[/+][-] ## Code to Reproduce[/-] [+]private readonly IPageDialogService _dialogService;[/+] [-]### MainPageViewModel.cs[/-] [+]public MainPageViewModel(IPageDialogService dialogService)[/+][-] csharp[/-]
[+]{[/+][-] using Prism.Commands;[/-]
[+]_dialogService = dialogService;[/+][-] using Prism.Mvvm;[/-]
[+]ShowDialogCommand = new DelegateCommand(OnShowDialog);[/+][-] using Prism.Services;[/-]
[+]}[/+]
[-]namespace PrismBugSample;[/-]
[+]public DelegateCommand ShowDialogCommand { get; }[/+]
[-]public class MainPageViewModel : BindableBase[/-]
[+]private async void OnShowDialog()[/+][-] {[/-]
[+]{[/+][-] private readonly IPageDialogService _dialogService;[/-]
[+]// This crashes in .NET 10 with ArgumentNullException[/+]
[+]await _dialogService.DisplayAlertAsync("Title", "Message", "OK", "Cancel");[/+][-] public MainPageViewModel(IPageDialogService dialogService)[/-]
[+]}[/+][-] {[/-]
[+]}[/+][-] _dialogService = dialogService;[/-]
[+][/+][-] ShowDialogCommand = new DelegateCommand(OnShowDialog);[/-] [-]}[/-] [+]## Relevant Log Output[/+] [+][/+][-] public DelegateCommand ShowDialogCommand { get; }[/-]
[+]FATAL EXCEPTION: main[/+]
[+]Process: SimplePrismDialogApp.SimplePrismDialogApp, PID: 20105[/+][-] private async void OnShowDialog()[/-]
[+]android.runtime.JavaProxyThrowable: [System.ArgumentNullException]: Value cannot be null. (Parameter 'cancel')[/+][-] {[/-]
[+]at Microsoft.Maui.Controls.Page.DisplayAlertAsync + 0x16(Unknown Source)[/+][-] // This crashes in .NET 10 with ArgumentNullException[/-]
[+]at Microsoft.Maui.Controls.Page.DisplayAlert + 0x0(Unknown Source)[/+][-] await _dialogService.DisplayAlertAsync("Title", "Message", "OK", "Cancel");[/-]
[+]at Prism.Services.PageDialogService.DisplayAlertAsync + 0x0(Unknown Source)[/+][-] }[/-]
[+]at Prism.Services.PageDialogService.DisplayAlertAsync + 0x0(Unknown Source)[/+][-] }[/-]
[+]at PrismBugSample.MainPageViewModel+d__5.MoveNext + 0xf(Unknown Source)[/+][-] [/-] [+]at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw + 0x11(Unknown Source)[/+] [+]at System.Threading.Tasks.Task+<>c.<ThrowAsync>b__128_0 + 0x0(Unknown Source)[/+][-] ## Relevant Log Output[/-] [+]at Android.App.SyncContext+<>c__DisplayClass2_0.<Post>b__0 + 0x0(Unknown Source)[/+][-] [/-]
[+][/+][-] FATAL EXCEPTION: main[/-] [-]Process: SimplePrismDialogApp.SimplePrismDialogApp, PID: 20105[/-] [+]## Analysis[/+][-] android.runtime.JavaProxyThrowable: [System.ArgumentNullException]: Value cannot be null. (Parameter 'cancel')[/-] [+]Investigation reveals:[/+][-] at Microsoft.Maui.Controls.Page.DisplayAlertAsync + 0x16(Unknown Source)[/-] [-]at Microsoft.Maui.Controls.Page.DisplayAlert + 0x0(Unknown Source)[/-] [+]- Input parameters are clearly non-null ("OK", "Cancel")[/+][-] at Prism.Services.PageDialogService.DisplayAlertAsync + 0x0(Unknown Source)[/-] [+]- Direct MAUI call with same parameters works fine[/+][-] at Prism.Services.PageDialogService.DisplayAlertAsync + 0x0(Unknown Source)[/-] [+]- Prism's internal processing somehow converts the cancel parameter to null[/+][-] at PrismBugSample.MainPageViewModel+<OnShowDialog>d__5.MoveNext + 0xf(Unknown Source)[/-] [+]- .NET 10's stricter null checking makes this issue visible[/+][-] at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw + 0x11(Unknown Source)[/-] [-]at System.Threading.Tasks.Task+<>c.<ThrowAsync>b__128_0 + 0x0(Unknown Source)[/-] [+]### Steps to Reproduce[/+][-] at Android.App.SyncContext+<>c__DisplayClass2_0.<Post>b__0 + 0x0(Unknown Source)[/-] [-][/-]
[+]1. Create a File > New App (.NET MAUI project with .NET 10.0.100-preview.3.25201.16)[/+]
[+]2. Add Prism.DryIoc.Maui package version 9.0.537[/+][-] ## Analysis[/-]
[+]3. Create a ViewModel with PageDialogService dependency injection[/+][-] Investigation reveals:[/-]
[+]4. Add a Button with command binding to call DisplayAlertAsync[/+]
[+]5. Implement the DisplayAlertAsync call: await _dialogService.DisplayAlertAsync("Title", "Message", "OK", "Cancel");[/+][-] - Input parameters are clearly non-null ("OK", "Cancel")[/-]
[+]6. Run the app on Android emulator[/+][-] - Direct MAUI call with same parameters works fine[/-]
[+]7. Tap the button and observe[/+][-] - Prism's internal processing somehow converts[/-] the[+] crash 🐞[/+][-] cancel parameter to null[/-]
[-]- .NET 10's stricter null checking makes this issue visible[/-]
[+]Expected outcome: Dialog should display normally with "OK" and "Cancel" buttons, allowing user interaction[/+]
[+]Actual outcome: App crashes with ArgumentNullException: Value cannot be null. (Parameter 'cancel')[/+][-] ### Steps to Reproduce[/-]
[+]### Platform with bug[/+][-] 1. Create a File > New App (.NET MAUI project with .NET 10.0.100-preview.3.25201.16)[/-]
[-]2. Add Prism.DryIoc.Maui package version 9.0.537[/-]
[+].Net MAUI[/+][-] 3. Create a ViewModel with PageDialogService dependency injection[/-]
[-]4. Add a Button with command binding to call DisplayAlertAsync[/-]
[+]### Affected platforms[/+][-] 5. Implement the DisplayAlertAsync call: await _dialogService.DisplayAlertAsync("Title", "Message", "OK", "Cancel");[/-]
[-]6. Run the app on Android emulator[/-]
[+]Android[/+][-] 7. Tap the button and observe the crash 🐞[/-]
[+]### Did you find any workaround?[/+][-] Expected outcome: Dialog should display normally with "OK" and "Cancel" buttons, allowing user interaction[/-]
[-]Actual outcome: App crashes with ArgumentNullException: Value cannot be null. (Parameter 'cancel')[/-]
[+]No, there is no practical workaround. While it's technically possible to bypass Prism and call MAUI's DisplayAlert directly, this defeats the purpose of using Prism's abstraction and testability benefits, so it's not a viable solution.[/+]
[-]### Platform with bug[/-]
[+]### Relevant log output[/+]
[-].Net MAUI[/-]
[+]shell[/+] [-]### Affected platforms[/-] [+][/+]
[-]Android[/-]
[-]### Did you find any workaround?[/-]
[-]No response[/-]
[-]### Relevant log output[/-]
[-]shell[/-] [-]

[nightfairy5831]

This does not seem to be caused by Prism. MAUI is dropping a parameter in a DisplayAlert overload, which results in the problematic ArgumentNullException.

GitHub Issue: dotnet/maui#31473

I already contributed a PR in order to fix that: dotnet/maui#31474