Validation is one of the greatest security features to prevent your website against spam. We can do validation in two ways. One is from client-side and another is from server-side validation. Now here in this tutorial, I’ll explain how to proceed with dropdownlist validation from client-side using JavaScript in asp.net.
In my previous tutorials, I’d explained how to validate dropdownlist using jquery, validate radiobuttonlist using javascript, validate checkboxlist using javascript and other more cracking tutorials on DropDownList, Asp.net here.
Now we are going to implement the code, follow the step by step guidelines to validate the drop down list.
Function To Validate Asp.net DropDownList Control – [JavaScript]
Here is the JavaScript function that we need to use to validate dropdown list:
function ValidateDropDownList() {
var isSelected = false;
var ddlImageFormatVal = document.getElementById(“<%=ddlImageFormat.ClientID%>“).value;
if (ddlImageFormatVal > 0) {
//Selected option from dropdownlist
isSelected = true;
} else {
//Not selected so alert user to select any option
alert(“Please select image format from the list.”);
}
return isSelected;
}
</script>
HTML Markup For DropDownList Validation – [.aspx]
Following is the complete HTML Markup code for .aspx page:
<head id=”Head1″ runat=”server”>
<title>DropDownList Validation using JavaScript</title>
<script type=”text/javascript”>
function ValidateDropDownList() {
var isSelected = false;
var ddlImageFormatVal = document.getElementById(“<%=ddlImageFormat.ClientID%>“).value;
if (ddlImageFormatVal > 0) {
//Selected option from dropdownlist
isSelected = true;
} else {
//Not selected so alert user to select any option
alert(“Please select image format from the list.”);
}
return isSelected;
}
</script>
</head>
<body>
<form id=”form1″ runat=”server”>
<div>
<table>
<tr>
<td>Select Image Format</td>
<td>:</td>
<td>
<asp:DropDownList ID=”ddlImageFormat” runat=”server” RepeatDirection=”Horizontal”>
<asp:ListItem Value=”0″ Text=”Please select” />
<asp:ListItem Value=”1″ Text=”.jpg” />
<asp:ListItem Value=”2″ Text=”.png” />
<asp:ListItem Value=”3″ Text=”.gif” />
</asp:DropDownList>
</td>
</tr>
<tr>
<td colspan=”3″> </td>
</tr>
<tr>
<td colspan=”2″> </td>
<td>
<asp:Button ID=”btnSave” OnClientClick=”return ValidateDropDownList();”
runat=”server” Text=”Save” />
</td>
</tr>
</table>
</div>
</form>
</body>
</html>
In above sample code, you can examine that I have used OnClientClick=”return ValidateDropDownList();” which means we are calling a ValidateDropDownList() function on client-click event of btnSave and evaluate image type is selected or not from the dropdownlist to validate the dropdown or dropdownlist in asp.net.
Example Result
