Page A pops a new window called Page B.

How would I set the text value of Page A's TextBox from Page B's button click event?

I want to do this all on the code behind.

I tried doing this on Page B but to no avail.

Code:
    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'Put user code to initialize the page here
        Dim myControl1 As Control = FindControl("Calendar1")
        Dim myControl2 As Control = myControl1.Parent()
        Dim parent As Control = Page.Parent
        Response.Write(myControl2.ID)
    End Sub