AutoPostBack issue in DropDownList Event

Question

Sir,

 

I have going through a function in My ASP.NET Project  to fill GridView as per the selection in DropDownList item.

 

I could not get the proper  data because of AutoPostBack fires everytime. i.e  the DataValueField and DataTextField value of DropDown always being the value of first row.

 

Data in DropDownlist are :-

 

 

 

The issue is suppose I select mobile from DropDownList , the AutoPostBack event fires and the value turn from productId 3 to 1 . 

 the function which I write in c# to load the GridView is :-

 

 

 

 Please help me to solve this issue.