Why do RelayCommands typically use lazy initialization?

问题

When using Josh Smith's RelayCommand, most of the examples I've seen use lazy initialization such as:

public class ViewModel
{
    private ICommand myCommand;

    public ICommand MyCommand
    {
        get
        {
            if (myCommand == null)
            {
                myCommand = new RelayCommand(p => DoSomething() );
            }

            return myCommand;
        }
    }
    // ... stuff ...

}

Rather than creating the RelayCommand in the constructor, like this:

public class ViewModel
{
    public ViewModel()
    {
            MyCommand = new RelayCommand(p => DoSomething());
    }

    public ICommand MyCommand
    {
        get;
        private set;

    }

    // ... stuff ...
}

What's the benefit of using lazy initialization here? It will have to call the get property when setting up the binding, so I can't seen a reason to use this method over settings things up in the constructor.

Am I missing something here?

回答1:

Actually, WPF and Silverlight will get the relay command just once per binding, so you don't really need to store a backing field at all:

public ICommand MyCommand
{
    get
    {
        return new RelayCommand(p => DoSomething());
    }
}

So while there's nothing wrong with creating it in the .ctor as you suggest, there's very little reason to.

来源：https://stackoverflow.com/questions/3769918/why-do-relaycommands-typically-use-lazy-initialization