Create a new ICommand object in the ViewModel

Both ICommand objects are bound to a ViewModel.

The first approach seems to be used often.

But the second one saves some lines of code but would it not create everytime a new ICommand object when the Binding is refreshed so i开发者_如何转开发ts a waste of resources?!

private LightCommand _deleteDocumentCommand;
        public LightCommand DeleteDocumentCommand
        {
            get { return _deleteDocumentCommand ?? (_deleteDocumentCommand = new LightCommand(() => DeleteDocument(), () => CanDeleteDocument)); }
        }

        public LightCommand DeleteDocumentCommand
        {
            get { return new LightCommand(() => DeleteDocument(), () => CanDeleteDocument); }
        }

Yes your 2nd method creates a new command every time the command is referenced, but I also find your 1st method rather hard to read.

My preferred way to make a command in the ViewModel is

private LightCommand _deleteDocumentCommand;
public LightCommand DeleteDocumentCommand
{
    get 
    {
        if (_deleteDocumentCommand == null)
        {
            _deleteDocumentCommand = new LightCommand(
                () => DeleteDocument(), () => CanDeleteDocument);
        }

        return _deleteDocumentCommand;
    }
}

It might be more lines of code, but it is easy to read and understand. Besides, usually all my public Properties/Commands are generated by macros and dumped into a #region Properties area that stays collapsed the entire time I work with the ViewModel, so I don't have to scroll through pages of get/set methods.

yes it would. You are better off instantiating it once, so that you have something like this:

LightCommand DeleteCommand { get;  set;}

and then in our VM instantiation you assign to it. Or you could use your first example.

I assume you're looking for verification, and that's correct:

Everytime the Binding is refreshed, (or the command is called), a new object is instantiated. It looks like a clear waste of resources.