How to do loose coupling of command programmatically?

Question

I am making a mobile app using Xamarin. And using Prism to achieve MVVM with loose binding between Views and ViewModels. In one View, I am creating buttons programmatically from the code behind, like so:

var button = new Button {
  Text = e.ToString(),
  Command = 
};                
Container.Children.Add(button);

The buttons get created, but I have yet to find a way to bind the command property to a command on the ViewModel. I want to bind this loosely. According to MVVM the View cannot know anything about the ViewModel. Would things change a lot if I also wanted to parameterize the command? Is there a way to achieve this? Any help would be appreciated.

"According to MVVM the View cannot know anything about the ViewModel." Where did you read this? And why do you think this is the case? — Euphoric, Oct 21 '19 at 08:12
The View can have knowledge of both the ViewModel and the Model. The ViewModel ideally shouldn't have knowledge of the View and the Model shouldn't have knowledge of the ViewModel. — Michael Phillips, Oct 21 '19 at 08:34
Also, I'd always prefer binding an items control, list box etc. to some list on the view model to creating buttons in code behind, that's anti-mvvm. — Haukinger, Oct 21 '19 at 08:36
In the end we decided on buttons defined in XAML, using Command="{Binding someCommand}" to bind them to commands. Thanks for the help guys. Also, why the down vote? Is it because I didn't completely understand MVVM? — Martijn, Nov 14 '19 at 10:13

score 1 · Answer 1 · answered Oct 22 '19 at 02:43

you could create the Command in your ViewModel,then uses a Command property to set the binding in your View,for example:

in your View(your page):

LoginViewModel viewModel = new LoginViewModel();
BindingContext = viewModel
Button loginButton = new Button
 {
   Text = "LOGIN",
 };
loginButton.SetBinding(Button.CommandProperty, new Binding("LoginFormCommand"));

in ViewModel (LoginViewModel):

public class LoginFormViewModel 
 {
   public ICommand LoginFormCommand { get; private set; }
   private string _user;
   private string _pass;
   public LoginViewModel()
     {
      LoginFormCommand = new Command(LogUserIn());
     }
   public string User {
    get => _user; 
    set
     {
      if (_userName != value){ _userName = value;}
      OnPropertyChanged();
     }
    }
  public string Pass {
   get => _pass; 
   set
    {
     if (_userName != value){ _userName = value;}
     OnPropertyChanged();
    }
  }
 public LogUserIn()
  {
   bool IamLoggedIn = AFunctionThatCallsAWebService(User, Pass);
  }
 }

How to do loose coupling of command programmatically?

1 Answers1