Call Method in Master Page

From within the Page you can cast the Master page to a specific type (the type of your own Master that exposes the desired functionality), using as to side step any exceptions on type mismatches:

var master = Master as MyMasterPage;
if (master != null)
{
    master.Method();
}

In the above code, if Master is not of type MyMasterPage then master will be null and no method call will be attempted; otherwise it will be called as expected.

Use the MasterType directive like e.g.:

<%@ MasterType VirtualPath="~/masters/SourcePage.master" %>

Then you can use the method like this:

Master.Method();

You can simply do like...

MasterPageClassName MasterPage = (MasterPageClassName)Page.Master;
MasterPage.MasterMethod();

Check for Details ACCESS A METHOD IN A MASTER PAGE WITH CODE-BEHIND

MyMasterPageType master = (MyMasterPageType)this.Master;
master.MasterPageMethod();