What is a good way to update a control's property

See more:

WPF

MVVM

data-binding

Hi Guys, I have just (luckily) put together a simple working application with WPF MVVM. I understood (kind of) the gist of it, but there are still a few things that I still can't get around to

Suppose in:

private string firstname;

public string FirstName
{
     get {return firstname;}
     set
       {
          if ( value != firstname)
           {
              firstname = value;
           }
           OnPropertyChanged("FirstName");
       }
}

So if I'm not mistaken, when we set a value into FirstName, the OnPropertyChanged() will update the bound property in the view and change its value.

But when I try it in the get{}, I get the warning code is unreachable. I had planned to pull out a value from get and then set off OnPropertyChanged(). What I currently did in my viewmodel is this:

private Person p;

public string Id
{
    get {return p.Id;}
    set 
      {
         if (value != p.Id)
          {
             p.ID = value;
          }
          OnPropertyChanged("Id");
      }
}

public string FirstName
{
    get {return p.FirstName;}
}

protected void GetFirstName()
{
     Id = "PR001";
     OnPropertyChanged("FirstName");
}

Is there another way to do this or do I need to keep on calling OnPropertyChanged() whenever I want to update the property in the view?