启用和禁用下拉列表

Question

I have a web form with two drop down lists.

1. The 1st drop down list contains 2 values &
2. the 2nd drop down list contains 3 values.

My objective is, when I select the 1st value of the 1st drop down list , the 2nd dropdownlist should not be visible , but when i select the 2nd value of the 1st dropdownlist , the 2nd dropdownlist should appear .

Answer 1

You need to set the AutoPostBack-property of your first drop down list to true and add an OnSelectedIndexChanged-EventHandler

<asp:DropDown id="FirstList" runat="server" AutoPostBack="true" OnSelectedIndexChanged="FirstList_Changed"></asp:DropDown>

In your EventHandler you can check the selected index and act accordingly.

protected void FirstList_Changed(object sender, EventArgs e) {
    if(FirstList.SelectedIndex == 0) {
        SecondList.Visible = false;
    } else {
        SecondList.Visible = true;
    }
}

However you can also do the same thing with JavaScript (see BPX's solution).

Answer 2

You can do it by using JQuery. A sample code is given below.

$("#DropDownList1").change(function(){
    indx = $("#DropDownList1 option:selected").index();
    if(indx==1)
    {
      $("#DropDownList2").hide();
    }
    else
    {
      $("#DropDownList2").show();
    }
})

Don't forget to add jquery plugin.

Answer 3

If you want to enable and disable you can use this Code

 <asp:DropDownList ID="ddl1" runat="server" AppendDataBoundItems="true" AutoPostBack="true" Width="100%">
                    <asp:ListItem Text="" ></asp:ListItem>
                    <asp:ListItem Text="Value 1" Value="1"></asp:ListItem>
                    <asp:ListItem Text="Value 2" Value="2"></asp:ListItem>
                </asp:DropDownList>

You need to set AutoPostBack="true" and in the SelectedIndexChanged write this code

 protected void ddl1_SelectedIndexChanged(object sender, EventArgs e)
    {

            try
            {
                if (ddl1.SelectedValue == "1")
            {
                ddl2.Enabled = false;
                //ddl2.Visible = false;
            }
            else
            {
                ddl2.Enabled = true;
                //ddl2.Visible = true;
            }
            }
            catch (Exception ex)
            {
               string b=  ex.Message;
            }

    }

For VISIBLE * enabling/disabling * USE the commented line and comment the other line

Hope this helps

Happy coding