Set Date in TextBox when TextMode is Date in ASP.Net GridView editing using C# and VB.Net

i fixed

i must change

"{0:yyyy/MM/dd}")

to 

"{0:yyyy-MM-dd}"

Dear Kankon,

Please refer below Sample.

Database

For this example I have used of Northwind database that you can download using the link given below.

Download Northwind Database

HTML

<asp:GridView runat="server" ID="gvEmployees" AutoGenerateColumns="false" OnRowEditing="OnRowEditing"
    OnRowCancelingEdit="OnRowCancelingEdit">
    <Columns>
        <asp:BoundField HeaderText="Employee Id" DataField="EmployeeID" ReadOnly="true" />
        <asp:BoundField HeaderText="First Name" DataField="FirstName"/>
        <asp:BoundField HeaderText="Last Name" DataField="LastName"  />
        <asp:TemplateField HeaderText="Hire Date">
            <ItemTemplate>
                <asp:Label Text='<%# Eval("HireDate","{0:yyyy-MM-dd}") %>' runat="server" />
            </ItemTemplate>
            <EditItemTemplate>
                <asp:TextBox runat="server" Text='<%# Eval("HireDate","{0:yyyy-MM-dd}") %>' TextMode="Date"  />
            </EditItemTemplate>
        </asp:TemplateField>
        <asp:CommandField ButtonType="Button" ShowEditButton="true" ShowCancelButton="true" HeaderText="Modify" />
    </Columns>
</asp:GridView>

Namespaces

C#

using System.Data;	
using System.Data.SqlClient;
using System.Configuration;

VB.Net

Imports System.Data
Imports System.Configuration
Imports System.Data.SqlClient

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if(!this.IsPostBack)
    {
        this.BindGrid();
    }
}

private void BindGrid ()
{
    string conString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(conString))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT EmployeeId, FirstName, LastName, HireDate From Employees", con))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
            {
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);
                    gvEmployees.DataSource = dt;
                    gvEmployees.DataBind();
                }
            }
        }
    }
}

protected void OnRowEditing (object sender, GridViewEditEventArgs e)
{
    gvEmployees.EditIndex = e.NewEditIndex;
    this.BindGrid();
}

protected void OnRowCancelingEdit (object sender, GridViewCancelEditEventArgs e)
{
    gvEmployees.EditIndex = -1;
    this.BindGrid();
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Me.BindGrid()
    End If
End Sub

Private Sub BindGrid()
    Dim conString As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Using con As SqlConnection = New SqlConnection(conString)
        Using cmd As SqlCommand = New SqlCommand("SELECT EmployeeId, FirstName, LastName, HireDate From Employees", con)
            Using sda As SqlDataAdapter = New SqlDataAdapter(cmd)
                Using dt As DataTable = New DataTable()
                    sda.Fill(dt)
                    gvEmployees.DataSource = dt
                    gvEmployees.DataBind()
                End Using
            End Using
        End Using
    End Using
End Sub

Protected Sub OnRowEditing(ByVal sender As Object, ByVal e As GridViewEditEventArgs)
    gvEmployees.EditIndex = e.NewEditIndex
    Me.BindGrid()
End Sub

Protected Sub OnRowCancelingEdit(ByVal sender As Object, ByVal e As GridViewCancelEditEventArgs)
    gvEmployees.EditIndex = -1
    Me.BindGrid()
End Sub

Screenshot