Set DropDownList item based on Date selection using C# and VB.Net in ASP.Net

Hi nauna,

Check this example. Now please take its reference and correct your code.

HTML

<asp:TextBox ID="TextBox1" runat="server" TextMode="Date"
    OnTextChanged="DateChanged" AutoPostBack="true"></asp:TextBox>
<asp:DropDownList runat="server" ID="ddlTimes">
</asp:DropDownList>

Code

C#

protected void DateChanged(object sender, EventArgs e)
{
    DateTime selectedDate = Convert.ToDateTime(TextBox1.Text.Trim());
    List<ListItem> times = GetTime();
    for (int i = times.Count; i > 0; --i)
    {
        DateTime dt;
        if (!DateTime.TryParse(times[i - 1].Text, out dt)) { }

        if (dt <= DateTime.Now && selectedDate == DateTime.Today)
        {
            times.RemoveAt(i - 1);
        }
    }
    ddlTimes.DataSource = times;
    ddlTimes.DataTextField = "Text";
    ddlTimes.DataValueField = "Value";
    ddlTimes.DataBind();
}

private List<ListItem> GetTime()
{
    List<ListItem> times = new List<ListItem>();
    TimeSpan timeSpan = new TimeSpan(12, 00, 00);
    string time = DateTime.Today.Add(timeSpan).ToString("hh:mm tt");
    times.Add(new ListItem { Text = time, Value = time });
    timeSpan = new TimeSpan(14, 00, 00);
    time = DateTime.Today.Add(timeSpan).ToString("hh:mm tt");
    times.Add(new ListItem { Text = time, Value = time });
    timeSpan = new TimeSpan(17, 00, 00);
    time = DateTime.Today.Add(timeSpan).ToString("hh:mm tt");
    times.Add(new ListItem { Text = time, Value = time });
    timeSpan = new TimeSpan(19, 00, 00);
    time = DateTime.Today.Add(timeSpan).ToString("hh:mm tt");
    times.Add(new ListItem { Text = time, Value = time });
    timeSpan = new TimeSpan(08, 00, 00);
    time = DateTime.Today.Add(timeSpan).ToString("hh:mm tt");
    times.Add(new ListItem { Text = time, Value = time });
    timeSpan = new TimeSpan(10, 00, 00);
    time = DateTime.Today.Add(timeSpan).ToString("hh:mm tt");
    times.Add(new ListItem { Text = time, Value = time });

    return times;
}

VB.Net

Protected Sub DateChanged(ByVal sender As Object, ByVal e As EventArgs)
    Dim selectedDate As DateTime = Convert.ToDateTime(TextBox1.Text.Trim())
    Dim times As List(Of ListItem) = GetTime()
    For i As Integer = times.Count To 1 Step -1
        Dim dt As DateTime
        If Not DateTime.TryParse(times(i - 1).Text, dt) Then
        End If
        If dt <= DateTime.Now AndAlso selectedDate = DateTime.Today Then
            times.RemoveAt(i - 1)
        End If
    Next

    ddlTimes.DataSource = times
    ddlTimes.DataTextField = "Text"
    ddlTimes.DataValueField = "Value"
    ddlTimes.DataBind()
End Sub

Private Function GetTime() As List(Of ListItem)
    Dim times As List(Of ListItem) = New List(Of ListItem)()
    Dim timeSpan As TimeSpan = New TimeSpan(12, 0, 0)
    Dim time As String = DateTime.Today.Add(timeSpan).ToString("hh:mm tt")
    times.Add(New ListItem With {.Text = time, .Value = time})
    timeSpan = New TimeSpan(14, 0, 0)
    time = DateTime.Today.Add(timeSpan).ToString("hh:mm tt")
    times.Add(New ListItem With {.Text = time, .Value = time})
    timeSpan = New TimeSpan(17, 0, 0)
    time = DateTime.Today.Add(timeSpan).ToString("hh:mm tt")
    times.Add(New ListItem With {.Text = time, .Value = time})
    timeSpan = New TimeSpan(19, 0, 0)
    time = DateTime.Today.Add(timeSpan).ToString("hh:mm tt")
    times.Add(New ListItem With {.Text = time, .Value = time})
    timeSpan = New TimeSpan(8, 0, 0)
    time = DateTime.Today.Add(timeSpan).ToString("hh:mm tt")
    times.Add(New ListItem With {.Text = time, .Value = time})
    timeSpan = New TimeSpan(10, 0, 0)
    time = DateTime.Today.Add(timeSpan).ToString("hh:mm tt")
    times.Add(New ListItem With {.Text = time, .Value = time})
    Return times
End Function

Screenshot