Multi Columns filtered gridview

I have a filtere code that works like charm for only one column. What I need is that i want my code to filter 2 or 3  columns at the same time,

 

Here is my code:

 

 I want to add another column filter as following;

 

 an a third column filter as following;

 

 but EmployeeID.Text value will come from frmMain.Employee.Text

 

 

How can I do this

Thanks