Want to fetch data from Gridview to varible for Update event

I want to fetch different data parameters from Gridview to following varible ,and use

int rptId = Int32.Parse(GridView1.DataKeys[e.RowIndex].Value.ToString());

string client = GridView1.DataKeys[e.RowIndex].Value.ToString();

string counterparty = GridView1.DataKeys[e.RowIndex].Value.ToString();

DateTime scheduledate = DateTime.Parse(GridView1.DataKeys[e.RowIndex].Value.ToString());

DateTime scheduletime = DateTime.Parse(GridView1.DataKeys[e.RowIndex].Value.ToString());

such code to implement above cited condition ,but getting exception like "Index was out of range. Must be non-negative and less than the size of the collection.

Parameter name: index".

Can you help me out.