How to display data of grid view in to textbox whenever user click on edit option in gridview

<div class="form-group" >
     ENTER EMPLOYEE ID :
     <asp:TextBox ID="TextBox1" placeholder="Employee ID" CssClass="form-control" width="400px" runat="server"></asp:TextBox>
     <br />
     <br />
     ENTER FIRSTNAME :
     <asp:TextBox ID="TextBox2" placeholder="First name" CssClass="form-control" width="400px" runat="server"></asp:TextBox>
     <br />
     <br />
     ENTER LASTNAME :
     <asp:TextBox ID="TextBox3" placeholder="Last name" CssClass="form-control" width="400px" runat="server"></asp:TextBox>
     <br />
     <br />
     ENTER ADDRESS:
     <asp:TextBox ID="TextBox4" placeholder="Address" CssClass="form-control" width="400px" runat="server"></asp:TextBox>
     <br />
      <br />
      <br />
     ENTER CITY:
     <asp:TextBox ID="TextBox5" placeholder="city" CssClass="form-control" width="400px" runat="server"></asp:TextBox>
     <br />
      <br />
      <br />
         <table>
            <tr> <td><asp:Button ID="Button1" runat="server"  Text="Save" Width="70px" BackColor=" Lightblue" OnClick="Button1_Click"/></td>
                 <td style="padding-left:20px;"></td>
                <td><asp:Button ID="Button2" runat="server"  Text="Cancel" Width="60px"  BackColor=" Lightblue" OnClick="Button2_Click" Height="26px"/></td>
                 <td style="padding-left:20px;"></td>
                <%--<td> <asp:Button ID="Button4" runat="server"  Text="Update" Width="60px"  BackColor=" Lightblue" OnClick="Button4_Click" Height="27px"/></td>--%>
            </tr>
         </table>
            <br />
             <br />
         <%--Start--%>
         <table>
             <tr>
                 <td>
             <asp:GridView ID="GridView3" runat="server"  AutoGenerateColumns="False"
                   BackColor="#DEBA84" BorderColor="#DEBA84" BorderStyle="None" BorderWidth="1px"
                   CellPadding="3" DataKeyNames="EmpID" AutoGenerateDeleteButton="True"
                   AutoGenerateEditButton="True" onrowcancelingedit="GridView3_RowCancelingEdit"
                   onrowdeleting="GridView3_RowDeleting" onrowediting="GridView3_RowEditing"
                   onrowupdating="GridView3_RowUpdating" CellSpacing="2" OnSelectedIndexChanged="GridView3_SelectedIndexChanged" onrowcommand="GridView3_RowCommand" >
                 <Columns>
                       <asp:TemplateField HeaderText="EmpID">
                           <EditItemTemplate>
                               <asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("EmpID") %>'></asp:TextBox>
                           </EditItemTemplate>
                            <ItemTemplate>
                               <asp:Label ID="Label1" runat="server" Text='<%# Bind("EmpID") %>'></asp:Label>
                           </ItemTemplate>
                            </asp:TemplateField>
                       <asp:TemplateField HeaderText="FirstName">
                           <EditItemTemplate>
                               <asp:TextBox ID="TextBox2" runat="server" Text='<%# Bind("FirstName") %>'></asp:TextBox>
                           </EditItemTemplate>
                            <ItemTemplate>
                               <asp:Label ID="Label2" runat="server" Text='<%# Bind("FirstName") %>'></asp:Label>
                                </ItemTemplate>
                            </asp:TemplateField>
                       <asp:TemplateField HeaderText="LastName">
                                <EditItemTemplate>
                               <asp:TextBox ID="TextBox3" runat="server" Text='<%# Bind("LastName") %>'></asp:TextBox>
                           </EditItemTemplate>
                            <ItemTemplate>
                               <asp:Label ID="Label3" runat="server" Text='<%# Bind("LastName") %>'></asp:Label>
                           </ItemTemplate>
                            </asp:TemplateField>
                       <asp:TemplateField HeaderText="Address">
                                <EditItemTemplate>
                               <asp:TextBox ID="TextBox4" runat="server" Text='<%# Bind("Address") %>'></asp:TextBox>
                           </EditItemTemplate>
                            <ItemTemplate>
                               <asp:Label ID="Label4" runat="server" Text='<%# Bind("Address") %>'></asp:Label>
                           </ItemTemplate>
                            </asp:TemplateField>
                       <asp:TemplateField HeaderText="City">
                                <EditItemTemplate>
                               <asp:TextBox ID="TextBox5" runat="server" Text='<%# Bind("City") %>'></asp:TextBox>
                           </EditItemTemplate>
                            <ItemTemplate>
                               <asp:Label ID="Label5" runat="server" Text='<%# Bind("City") %>'></asp:Label>
                           </ItemTemplate>
                           </asp:TemplateField>
                  </Columns>

protected void GridView3_RowCommand(object sender, GridViewCommandEventArgs e)
   {
       
           TextBox1.Text = gr.Cells[1].Text;
           TextBox2.Text = gr.Cells[2].Text;
           TextBox3.Text = gr.Cells[3].Text;
           TextBox4.Text = gr.Cells[4].Text;
           TextBox5.Text = gr.Cells[5].Text;
       }
   }