How does dependency injection work in Blazor components, and what's the difference between @inject and constructor injection?

Blazor components support DI via the @inject directive (syntactic sugar generating a property with [Inject] attribute) or explicit [Inject] properties, resolving services from the DI container when the component is instantiated -- components generally can't use constructor injection directly since the framework controls their instantiation, unlike typical .NET classes.

@inject IUserService UserService
@inject NavigationManager Navigation

@code {
    protected override async Task OnInitializedAsync() {
        var user = await UserService.GetCurrentUserAsync();
        if (user == null) Navigation.NavigateTo("/login");
    }
}