How to pass string as command parameter from c# markup

Question

I am using C# markup for the UI development. I declared two buttons to enable user to select Language. The markup is as follows:

 FuncConverter<string, Color> stringToColorConverter = new FuncConverter<string, Color>(language => language == "English" ? Color.Blue : Color.Gray);
 new Button{Text="English"}.Bind(Button.BackgroundColorProperty,nameof(vm.SelectedLanguage),BindingMode.TwoWay,converter:stringToColorConverter).BindCommand(nameof(vm.ChangeLanguageCommand),"English"),

new Button{Text="हिंदी"}.Bind(Button.BackgroundColorProperty,nameof(vm.SelectedLanguage),BindingMode.TwoWay,converter:stringToColorConverter).BindCommand(nameof(vm.ChangeLanguageCommand), parameterPath:("हिंदी"))

The code in the ViewModel:

 public ReactiveCommand<string,string> ChangeLanguageCommand { get; set; }

ChangeLanguageCommand = ReactiveCommand.CreateFromTask<string,string>(async(selectedLanguage)=>await ChangeLanguage(selectedLanguage));

public async Task<string> ChangeLanguage(string selectedLanguage)
        {
            CultureInfo language = CultureInfo.GetCultures(CultureTypes.NeutralCultures).ToList().First(element => element.EnglishName.Contains(selectedLanguage));
            Thread.CurrentThread.CurrentUICulture = language;
            AppResources.Culture = language;
            return language.EnglishName;
        }

The button for English language does not invoke command. Whereas the button for Hindi language invoke command but the passed parameter is null. I am new to C# markup and there are very few resources on C# markup. Thanks in advance for any help.

Answer 1

Hi paramjit-0569,

Welcome to our Microsoft Q&A platform!

According to document: Xamarin Community Toolkit C# Markup, we can bind the command as followed.

new Button{Text="English"}.Row (0) .Column (0)  
    .Bind(BackgroundColorProperty,nameof(vm.SelectedLanguage),BindingMode.TwoWay,converter:stringToColorConverter)  
    .BindCommand (nameof(vm.TapCommand), vm, nameof(vm.SelectedLanguage)),  

Here is the full code demo you can refer to.
MainPage.xaml.cs

public partial class MainPage : ContentPage  
{  
    public MainPage()  
    {  
        InitializeComponent();  
  
        MainPageViewModel vm = new MainPageViewModel();  
        this.BindingContext = vm;  
  
        FuncConverter<string, Color> stringToColorConverter = new FuncConverter<string, Color>(language => language == "English" ? Color.Blue : Color.Gray);  
  
        Content = new Grid  
        {  
            Children =  
            {  
                new Button{Text="English"}.Row (0) .Column (0)  
                    .Bind(BackgroundColorProperty,nameof(vm.SelectedLanguage),BindingMode.TwoWay,converter:stringToColorConverter)  
                    .BindCommand (nameof(vm.TapCommand), vm, nameof(vm.SelectedLanguage)),  
  
                new Button{Text="हिंदी"} .Row (1) .Column (0)  
                    .Bind(Button.BackgroundColorProperty,nameof(vm.SelectedLanguage),BindingMode.TwoWay,converter:stringToColorConverter)  
                    .BindCommand(nameof(vm.TapCommand), vm, nameof(vm.SelectedLanguage))  
            }  
        };  
    }  
}  

MainPageViewModel.cs

class MainPageViewModel : INotifyPropertyChanged  
{  
    public ICommand TapCommand { get; private set; }  
    string selectedLanguage;  
    public string SelectedLanguage  
    {  
        get => selectedLanguage;  
        set  
        {  
            if (selectedLanguage == value || value == null)  
                return;  
            selectedLanguage = value;  
            OnPropertyChanged("SelectedLanguage");  
        }  
    }  
  
    public MainPageViewModel()  
    {  
        SelectedLanguage = "English";  
        TapCommand = new Command<object>(Tap);  
    }  
  
    void Tap(object obj)  
    {  
        Debug.WriteLine("Tap");  
        // get parameter  
        Debug.WriteLine(obj.ToString());  
        SelectedLanguage = SelectedLanguage == "English" ? "हिंदी" : "English";  
    }  
  
    public event PropertyChangedEventHandler PropertyChanged;  
    protected void OnPropertyChanged(string propertyName)  
    {  
        var handler = PropertyChanged;  
        if (handler != null)  
            handler(this, new PropertyChangedEventArgs(propertyName));  
    }  
}  

Regards,
Kyle

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