Comments on: Master the Basics of MVVM for Building WPF Applications

By: dr Vlad

dr Vlad — Mon, 28 Mar 2022 08:05:19 +0000

Thank you, this cleared a lot of the mess in my mind about it all. Time to rewrite the mess in my code now …

By: Kevin Bost

Kevin Bost — Wed, 10 Jun 2020 21:40:46 +0000

In reply to Eugen. Thanks Eugen, I have update the post to correct that.

By: Eugen

Eugen — Wed, 10 Jun 2020 21:34:29 +0000

I noticed a syntax error in the “We can implement it like this” section. A closing parenthesis is missing. It should be something like this:
public void OnPropertyChanged(string propertyName) => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

By: Steve Greene

Steve Greene — Wed, 31 Jul 2019 18:16:11 +0000

In reply to Kevin Bost.

Thank you! I remove the “=>” form of the FirstName setter and altered it back to a brace-block section, and added _changeNameCommand.InvokeCanExecuteChanged(); to the setter following the SetProperty method. Now, the moment FirstName is changed in any way to be different from “Walter”, the button is then re-enabled – it’s also automatically disabled when I manually type “Walter” in the FirstName field. This behavior seems more desirable to me.

By: Kevin Bost

Kevin Bost — Wed, 31 Jul 2019 16:06:09 +0000

In reply to Steve Greene. Hi Steve, With the way the code is written the button will not re-enable. To re-enable the command, there would need to be some code in the view model that changes the value of the FirstName property, and then call _changeNameCommand.InvokeCanExecuteChanged(); to notify the command (which will update the button) that its CanExecute delegate (in this case the CanChangeName method) should be invoked.

By: Steve Greene

Steve Greene — Wed, 31 Jul 2019 15:53:34 +0000

This command works exactly as described, for “attaching” the command to the Button and making the Button inactive. But I don’t understand how to make the Button active again. Once I click on the button, it then remains inactive no matter what.