How to change drop down list selected index and visibility using another drop down list in asp.net?

Question

I have a drop down list like this in my asp.net application,

<asp:DropDownList runat="server" ID="ddlChanges" CssClass="selectstyle" onchange="javascript:ddlChangesChanged();"> 
<asp:ListItem Text="-- Select -- " Value="-1"></asp:ListItem> 
<asp:ListItem Text="Status Change" Value="1"></asp:ListItem>
<asp:ListItem Text="Product Name Change" Value="2"></asp:ListItem>       
<asp:ListItem Text="Category Change" Value="3"></asp:ListItem>
</asp:DropDownList>

So, when user selects "Status Change" from the list, another dropdown list with following values appears,

<asp:DropDownList runat="server" ID="ddlStatus" CssClass="selectstyle"  Style="visibility: hidden;"> 
<asp:ListItem Text="-- Select -- " Value="-1"></asp:ListItem> 
<asp:ListItem Text="Pending" Value="1"></asp:ListItem>
<asp:ListItem Text="Fixed" Value="2"></asp:ListItem>       
<asp:ListItem Text="Cancelled" Value="3"></asp:ListItem>
</asp:DropDownList>

<asp:Button ID="btnUpdate" CssClass="selectstyle" runat="server" Text="Update" OnClick="btnUpdate_Click"></asp:Button>

If user does not select any value from the drop down list (ddlStatus), I am displaying an alert message ("You must select a status.") using JavaScript in the btnUpdate click event,

if (this.ddlStatus.SelectedItem.Value.Trim() == "-1")
{
    string script = "<script type=\"text/javascript\">alert('You must select a status.');</script>";
    ClientScript.RegisterClientScriptBlock(this.GetType(), "Alert", script);
}

But after this, my page refreshes and drop down list ddlChanges has "Status Change" (previously selected item) as selected item and drop down list (ddlStatus) gets hidden. I want ddlChanges drop down list to have -- Select -- as the selected item and ddlStatus should be visible.

How can I do that?

So why don't you reset your ddls to the required state inside the btnUpdate click? ddlStatus.Style= "visibility: hidden"; and ddlChanges.SelectedItem = ... — Eugene Podskal
Edit your question, you probably meant "...ddlChanges drop down list to have Status Change as the selected item and ddlStatus should be visible." — Nikola Bogdanović

Nikola Bogdanović Nikola Bogdanović · Accepted Answer · 2015-03-10T18:25:44

You are doing a full postback (all changes on client get reset, except the posted back input values) - so either do a client (javascript) validation (best option), or switch to ajax partial postback (faster option), or simply just change this (slowest option):

if (this.ddlStatus.SelectedItem.Value.Trim() == "-1")
{
    ddlStatus.Attributes["style"] = null;
    string script = "<script type=\"text/javascript\">alert('You must select a status.');</script>";
    ClientScript.RegisterClientScriptBlock(this.GetType(), "Alert", script);
}

How to change drop down list selected index and visibility using another drop down list in asp.net?

2 Answers