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wpfmvvmviewmodel

MVVM ICommand alternative

I have begun creating a wpf mvvm app. It seems a vital ingredient to the ViewModel is a bunch of ICommands to have a loosely coupled way of allowing the view to interact with the viewmodel.

My question is this, why can't I bind directly to a method?

I have used Josh Smith's RelayCommand implementation of ICommand that allows you to inject delgates into an ICommand object, but really, is there some easier way to allow a button push to call a method in the viewmodel?

I'm new to MVVM, I believe I need some enlightenment

Solution

  • You can't bind directly to a method because Button (for example) doesn't have a property that accepts a delegate. Instead, it has a Command property of type ICommand. A RelayCommand (aka DelegateCommand) is just an ICommand that wraps delegates.

    I see no technical reason why it wouldn't be possible for the view to bind to specific methods on the view model by way of a markup extension:

    <Button Command="{ViewModelMethod SomeMethodName}"/>

    However, this would be slower and would increase the coupling between the view and view model. If the view knows only about a property on the view model of type ICommand, the implementation of that command could change completely (or methods could be renamed) without the view being aware.