WPF Data Binding to changing object

Question

I have a user control which displays the currently logged in user's name. I have bound a TextBlock in the control to the UserId property of a User obejct in my application.

The issue I have is that the User object my binding has as a source changes each time a new user logs in.

I can think of a solution where I fire an event when the User obejct changes and this is caught my by control which then reinitialise's the binding but this seems less than ideal.

Are there a solution to this issue, I feel it must be very common?

Cheers,

James

Is it the User object that changes (if so, where is it set?) or is it the UserId that changes (on the same User instance)? — Marc Gravell
– Marc Gravell, Commented May 8, 2009 at 10:16
If the DataSource is changing, Setting the DataSource to the new object should automatically update bound controls. If a bound property is changing.. you need INotifyPropertyChanged — Gishu
– Gishu, Commented May 8, 2009 at 12:30

Emanuel · Accepted Answer · 2023-05-07 17:50:51Z

Most UI bindings already handle this via property notifications, in particular (for WPF) INotifyPropertyChanged. - i.e. if you are updating the UserId on a single instance:

class User : INotifyPropertyChanged {
   public event PropertyChangedEventHandler PropertyChanged;
   protected virtual void OnPropertyChanged(string propertyName) {
      PropertyChangedEventHandler handler = PropertyChanged;
      if(handler!=null) handler(this, new PropertyChangedEventArgs(
                                            propertyName));
   }
   private string userId;
   public string UserId {
       get {return userId;}
       set {
           if(userId != value) {
              userId = value;
              OnPropertyChanged("UserId");
           }
       }
   }
}

This should then update the binding automatically. If you are, instead, changing the actual user instance, then consider the same trick, but against whatever hosts the user:

public User User {
    get {return user;}
    set {
        if(user != value) {
            user = value;
            OnPropertyChanged("User");
        }
    }
}

And if you are binding to something's "User.UserId", then it should work.

Collectives™ on Stack Overflow

WPF Data Binding to changing object

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related