Thank you for the details.
Once you have created your UserControl, you can easily set it as a Content
of the RadWindow in the MainPage as follows:
MyUC uc = new MyUC();
RadWindow myWin = new RadWindow();
myWin.Content = uc;
Then, you can add the TextBox to the Content of the UserControl and set its Text
TextBox text = new TextBox();
text.Text = "My Text from the main page";
uc.Content = text;
And finally, show the RadWindow:
Hope this information helps. If you have further questions please let us know.
the Telerik team
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