how to access Viewstate in OnRowCommand event from Gridview

 How to access Viewstate in  OnRowCommand event from Gridview.
Below code update link not fire in click event... how to solve this
protected void grd_View_RowCommand(object sender, GridViewCommandEventArgs e) {
if(e.CommandName=="Update") {
DataTable dtss = new DataTable(); dtss =(DataTable)ViewState["test_data"];
}
}