Question

In my usercontrol ViewUser the groupbox header and textblock isnt displaying UserID?

Main Window:

private void btnGeneral_Click(object sender, RoutedEventArgs e)
{

    ViewUser myusercontrol = new ViewUser();
    String id = (String)((Button)sender).Tag;
    myusercontrol.UserID = id;
    PanelMainContent.Children.Add(myusercontrol);

}
 private void button1_Click(object sender, RoutedEventArgs e)
 {
         string uriUsers = "http://localhost:8000/Service/User";
            XDocument xDoc = XDocument.Load(uriUsers);
            var sortedXdoc = xDoc.Descendants("User")
                           .OrderByDescending(x => Convert.ToDateTime(x.Element("TimeAdded").Value));
            foreach (var node in xDoc.Descendants("User"))
            {

                Button btnFindStudent = new Button();
                btnUser.Click += this.btnGeneral_Click;
                btnUser.Tag = String.Format(node.Element("UserID").Value);
                //also tryed btnUser.Tag = node.Element("UserID").Value;

UserControl:

public partial class ViewUser : UserControl
{
    public ViewUser()
    {
        InitializeComponent();
    }
    private string _user;

    public string UserID
    {
        get { return _userID; }
        set { _userID = value; }
    }
    protected override void OnInitialized(EventArgs e)
    {
        base.OnInitialized(e);
        groupBox1.Header = UserID;
        textBlock1.Text = UserID;
    }
}

}

Answer 1

Kirsty, you should update the GroupBox and TextBlock every time the UserID property changes:

public string UserID 
{ 
    get { return _userID; } 
    set
    {
        _userID = value;
        groupBox1.Header = _userID; 
        textBlock1.Text = _userID; 
    } 
} 

Currently you’re updating the GroupBox and TextBlock only a single time in OnInitialized. But OnInitialized is called only once after the ViewUser control is initialized and never again.

This is what n8wrl meant with the second part of his answer.