String was not recognized as a valid DateTime on selected indexchange of gridview
below refere your provided solution Set TextMode Date value on GridView row selection using C# and VB.Net in ASP.Net
Now i define column in gridivew
<asp:GridView ID="gvv" runat="server" AutoGenerateSelectButton="true" AutoGenerateColumns="false" OnSelectedIndexChanged="gvv_SelectedIndexChanged" BackColor="White" BorderColor="#3366CC" BorderStyle="None" BorderWidth="1px" CellPadding="4">
<FooterStyle BackColor="#99CCCC" ForeColor="#003399" />
<HeaderStyle BackColor="#003399" Font-Bold="True" ForeColor="#CCCCFF" />
<PagerStyle BackColor="#99CCCC" ForeColor="#003399" HorizontalAlign="Left" />
<RowStyle BackColor="White" ForeColor="#003399" />
<SelectedRowStyle BackColor="#009999" Font-Bold="True" ForeColor="#CCFF99" />
<SortedAscendingCellStyle BackColor="#EDF6F6" />
<SortedAscendingHeaderStyle BackColor="#0D4AC4" />
<SortedDescendingCellStyle BackColor="#D6DFDF" />
<SortedDescendingHeaderStyle BackColor="#002876" />
<Columns>
<asp:TemplateField HeaderText="ID">
<ItemTemplate>
<asp:label ID="lbid" runat="server" Text='<%#Bind("ID")%>'></asp:label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Name">
<ItemTemplate>
<asp:label ID="lbname" runat="server" Text='<%#Bind("Name")%>'></asp:label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Designation">
<ItemTemplate>
<asp:label ID="lbdesignation" runat="server" Text='<%#Bind("designation")%>'></asp:label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Joining_Date">
<ItemTemplate>
<asp:label ID="lbDOJ" runat="server" Text='<%# Eval("DOJ", "{0:MM/dd/yyyy}") %>' ></asp:label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Salary">
<ItemTemplate>
<asp:label ID="lbsalary" runat="server" Text='<%#Bind("salary")%>'></asp:label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
protected void gvv_SelectedIndexChanged(object sender, EventArgs e)
{
lblastid.Text = gvv.SelectedRow.Cells[1].Text;
txtname.Text = gvv.SelectedRow.Cells[2].Text;
txtsalary.Text = gvv.SelectedRow.Cells[3].Text;
txtdoj.Text = Convert.ToDateTime(gvv.SelectedRow.Cells[5].Text).ToString("dd/MM/yyyy");
string des = gvv.SelectedRow.Cells[4].Text.Trim().Replace(" ", "");
txtdeduction.Text = gvv.SelectedRow.Cells[6].Text.Trim().Replace(" ", "");
ddldesignation.ClearSelection();
if (ddldesignation.Items.FindByText(des) != null)
{
// DDUOM.Items.FindByText(gvv.SelectedRow.Cells[4].Text).Selected = true;
ddldesignation.Items.FindByText(des).Selected = true;
}
