Referencing page controls from a class file?

so i have a website with a master page, default page and a class file. I have a button placed in the master page that when clicked should update a chart available in the default page. What i thought i should do is to create a function in the class file that updates the chart, and is called when the master page button is clicked. The only problem is I couldn't modify chart contents from the class file. Is there anyway i could access the default page chart from the class? Or is there a better way to handle this whole situation? Thank you