On postback, how can I add a error message to validation summary?

Question

Two questions:

On postback when a user clicks submit, how can I add a error message to validation summary?

Is it also possible to highlight a particular textbox using the built in .net validation controls?

Answer 1

Dynamically create a CustomValidator control and add it directly to the Page.Validators collection.

Dim err As New CustomValidator err.ValidationGroup = "MyGroup" err.IsValid = False err.ErrorMessage = "The password is invalid" Page.Validators.Add(err) 

Unlike adding the CustomValidator to the markup, this method allows you to add any number of arbitrary error messages based on server-side business logic.

Note that you can also add it to the page directly, but there are a couple of rules to follow:

1. You must add the control to the same naming container as the controls of the validation group.
2. If you don't want the validation message to appear in a random position in the page, you will either have to add the validator to a specific container or you will need to supress it using a CSS class or style.

You can also create a custom class and implement IValidator, which enables you to add the message with one line of code, but this method doesn't support Validation Groups.

Per Anders Fjeldstad's suggestion, here are a set of handy extension methods.

Imports Microsoft.VisualBasic Imports System.Runtime.CompilerServices  Public Module PageExtensions      <Extension()> _     Public Sub AddValidationError(ByVal p As System.Web.UI.Page, ByVal errorMessage As String)         p.AddValidationError(errorMessage, String.Empty)     End Sub      <Extension()> _     Public Sub AddValidationError(ByVal p As System.Web.UI.Page, ByVal errorMessage As String, ByVal validationGroup As String)         Dim err As New CustomValidator         err.ValidationGroup = validationGroup         err.ErrorMessage = errorMessage         err.IsValid = False         p.Validators.Add(err)     End Sub  End Module 

Answer 2

Add a custom validator and manually set it's IsValid and ErrorMessage properties. Sort of like this:

<asp:panel ID="ErrorsPanel" runat="server" CssClass="ErrorSummary">     <asp:CustomValidator id="CustomValidator1" runat="server"          Display="None" EnableClientScript="False"></asp:CustomValidator>     <asp:ValidationSummary id="ErrorSummary" runat="server"          HeaderText="Errors occurred:"></asp:ValidationSummary> </asp:panel> 

In the code behind:

// // Update the database with the changes // string ErrorDetails; if (!Db.Update(out ErrorDetails)) {     CustomValidator1.IsValid = false;     CustomValidator1.ErrorMessage = ErrorDetails; }