C
C#•2d ago
wildREA

How to Correctly Reference a Method in App.xaml.cs

Hey, reviewer. The ChangeLanguage method should work, but referencing is a challenge at the moment, since I get the error 'App' does not contain a definition for 'ChangeLanguage' and no accessible extension method 'ChangeLanguage' accepting a first argument of type 'App' could be found (are you missing a using directive or an assembly reference?). The OnLanguageChanged method works until I add that reference for ((App)Application.Current).... How do I correctly reference to a method in App.xaml.cs? ---- Settings.xaml.cs 
    public partial class Settings : UserControl
    {
        public Settings()
        {
            InitializeComponent();
        }

        private void OnLanguageChanged(object sender, SelectionChangedEventArgs e)
        {
            string? selectedLanguage = ((ComboBoxItem?)e.AddedItems[0]).Tag.ToString();
            Debug.WriteLine(selectedLanguage);
            ((App)Application.Current).ChangeLanguage(selectedLanguage);
        }
    }
}
    public partial class Settings : UserControl
    {
        public Settings()
        {
            InitializeComponent();
        }

        private void OnLanguageChanged(object sender, SelectionChangedEventArgs e)
        {
            string? selectedLanguage = ((ComboBoxItem?)e.AddedItems[0]).Tag.ToString();
            Debug.WriteLine(selectedLanguage);
            ((App)Application.Current).ChangeLanguage(selectedLanguage);
        }
    }
}
App.xaml.cs 
public partial class App : Application
{
    public void ChangeLanguage(string language)
    {
public partial class App : Application
{
    public void ChangeLanguage(string language)
    {
4 Replies
Nasdack
Nasdack•2d ago
You can use dependency injection or make the method static if it does not access instance data
wildREA
wildREAOP•2d ago
I have this and ServiceProvider is apparently not defined in App despite having defined it. I've used using Microsoft.Extensions.DependencyInjection;. Settings.xaml.cs 
// Access ChangeLanguage method via DI
var languageService = (IAppLanguageServices)App.ServiceProvider.GetService(typeof(IAppLanguageServices));
languageService?.ChangeLanguage(selectedLanguage);
// Access ChangeLanguage method via DI
var languageService = (IAppLanguageServices)App.ServiceProvider.GetService(typeof(IAppLanguageServices));
languageService?.ChangeLanguage(selectedLanguage);
App.xaml.cs 
// Static ServiceProvider
public static IServiceProvider ServiceProvider { get; private set; }

protected override void OnStartup(StartupEventArgs e)
{
    var serviceCollection = new ServiceCollection();

    // Registering App class as IAppLanguageServices
    serviceCollection.AddSingleton<IAppLanguageServices>(this);

    // Build the service provider
    ServiceProvider = serviceCollection.BuildServiceProvider();

    base.OnStartup(e);
}
// Static ServiceProvider
public static IServiceProvider ServiceProvider { get; private set; }

protected override void OnStartup(StartupEventArgs e)
{
    var serviceCollection = new ServiceCollection();

    // Registering App class as IAppLanguageServices
    serviceCollection.AddSingleton<IAppLanguageServices>(this);

    // Build the service provider
    ServiceProvider = serviceCollection.BuildServiceProvider();

    base.OnStartup(e);
}
'App' does not contain a definition for 'ServiceProvider'
Nasdack
Nasdack•2d ago
Check that you're referencing the correct App. ServiceProvider is static and public and it must be there. Although the best practice for a service locator class is for it to be encapsulated So create a static method that fetches the service Don't expose the actual ServiceProvider
wildREA
wildREAOP•2d ago
@Nasdack I'll try it on Monday at 8.

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