Getting error while trying to access a property in aspx page from a user control ascx

I am trying to access a variable from a aspx in user control as below

MyTestPage testPage = (MyTestPage)this.Parent;
testPage.ID // i am trying to accessing id which exists in the aspx page.

I am getting the following error while try to execute the above code

**Unable to cast object of type 'System.Web.UI.WebControls.ContentPlaceHolder' to type 'mynamespace.MyTestPage '.**

I am using master pages 开发者_开发百科in my project.

May i know where am i making the mistake. I am open to learn if you know any better technique to access a variable fro aspx page to ascx control

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Have a look this very good article, hope it will help you

Mastering Page-UserControl Communication

and

Trigger Page Methods from a User Control

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do this to access master page

    // Cast the loosely-typed Page.Master 
 MyTestPage  myMasterPage = Page.Master as MyTestPage; 

also check this

Master Page To Content Page Interaction