TodoApp.MAUI: Replace obsolete Page.DisplayAlert with DisplayAlertAsync in AlertService (CS0618) #516

Summary

Discovered while adding Windows CI coverage for TodoApp.MAUI in #510 (PR #514, build-samples-todoapp-windows.yml). Building the sample produces a CS0618 obsolete-API warning:

Services\AlertService.cs(14,12): warning CS0618: 'Page.DisplayAlert(string, string, string)' is obsolete: 'Use DisplayAlertAsync instead'

Root cause

samples/todoapp/TodoApp.MAUI/Services/AlertService.cs:14:

public Task ShowErrorAlertAsync(string title, string message, string cancel = "OK")
    => Application.Current!.Windows[0].Page!.DisplayAlert(title, message, cancel);

.NET MAUI has deprecated the Task-returning Page.DisplayAlert(string, string, string) overload in favor of Page.DisplayAlertAsync(string, string, string), as part of a broader naming-consistency pass adding an explicit Async suffix to async MAUI APIs. The compiler warning itself names the replacement.

Additional information needed

None — this is a like-for-like rename with an identical signature/return type (Task), so it should be a mechanical, low-risk change. Worth double-checking the DisplayAlertAsync overload signature against the installed Microsoft.Maui.Controls package version (10.0.40, per the .csproj) once picked up, in case the parameter list or overload set differs slightly from DisplayAlert.

Suggested fix

Replace the call with the non-obsolete equivalent:

public Task ShowErrorAlertAsync(string title, string message, string cancel = "OK")
    => Application.Current!.Windows[0].Page!.DisplayAlertAsync(title, message, cancel);

Related

• Add CI workflow to build Windows-only /samples heads (Phase 2 of #509) #510 / PR ci: add build-samples workflow for Phase 2 Windows-only heads (#510) #514 — Phase 2 Windows CI for /samples, where this warning was first surfaced (no CI previously built this project at all).