update tab control wpf from another class

See more:

C#

Visual-Studio

WPF

VS2010

good morning

I have two class
1-class Window1 : that contains the tab control added
2-class DesignerCanvas :must add a text in tab control
I then add the following code in the class DesignerCanvas

public  Window1 form;
      public  DesignerCanvas(Window1 form)
 {
     this.form = form;
 }
   public void SendBackward_Executed( object sender, ExecutedRoutedEventArgs e)
     {
         ((Window1)form).tabItem1.Content = "new text"  ;
     }

In class window1 I add the following code

private DesignerCanvas test = new DesignerCanvas();

and in the method public window1 I add:

public Window1()
       {
           InitializeComponent();
           test.form = this;
         //here is the error
           test.SendBackward_Executed(object sender , System.Windows.Input.ExecutedRoutedEventArgs e);

       }

is there any other way to call the method??