Enable Disable TextBox based on another TextBox value using C# and VB.Net in ASP.Net

Hi akhter,

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

HTML

<asp:TextBox ID="TextBox1" runat="server" />
<asp:Button ID="Button1" Text="Enable Disable" runat="server" OnClick="EnableDisable" />
<hr />
<asp:TextBox ID="TextBox2" runat="server" />

Code

C#

protected void EnableDisable(object sender, EventArgs e)
{
    TextBox2.Enabled = false;
    if (TextBox1.Text.Trim().ToLower() == "b")
    {
        TextBox2.Enabled = true;
    }
}

VB.Net

Protected Sub EnableDisable(sender As Object, e As System.EventArgs)
    TextBox2.Enabled = False
    If TextBox1.Text.Trim().ToLower() = "b" Then
        TextBox2.Enabled = True
    End If
End Sub

Screenshot

Note : I have used Button click event. As per your requirement write code in the event you want to implement.