12.3 Collections Reference | ASP.NET in a Nutshell, Second Edition

Controls

ControlCollection = Page.Controls

Provides access to the ControlCollection instance associated with the page, with which you can add or manipulate controls at runtime.

Parameter

ControlCollection: An object of type ControlCollection containing the controls associated with the page.

Example

The code example uses the Controls property to display the Count property of the ControlCollection class instance associated with the page. It then adds a new Label control to the collection and displays the updated Count property by using the new label.

Sub Page_Load( )    Message.Text = "There are currently " & Controls.Count & _       " controls on the page.<br/>"    Dim Message2 As New Label    Controls.AddAt(Controls.Count - 1, Message2)    Message2.Text = "There are now " & Controls.Count & _       " controls on the page." End Sub

Notes

As with the Session and Trace properties, while you can retrieve a local reference to the Controls collection associated with the page, it is more common to access this instance directly through the Controls property, as shown in the example.

Note that when adding a control to a page that already contains controls, using the AddAt method of the ControlCollection class allows more precise placement of the control when compared to the Add method, which simply places the control at the end of the collection. In the example, using the Add method would result in the output from the added Label control appearing after the page's closing </html> tag, which is not well-formed HTML and could cause the page to render incorrectly in some browsers.

Validators

ValidatorCollection = Page.Validators

Returns an instance of the ValidatorCollection class containing all the validator controls contained on the requested page. We can access each validator control by iterating the ValidatorCollection collection.

Parameter

ValidatorCollection: An object variable of type ValidatorCollection.

Example

The code example displays a Textbox control with a RequiredFieldValidator and RegularExpressionValidator control assigned to it. In Page_Load, the code iterates through the ValidatorCollection returned by the Validators property and displays the ID and ErrorMessage property of each validator in the collection:

<%@ Page Language="vb" %> <html>    <head>       <title></title>       <script runat="server">          Sub Page_Load( )             Dim Validator as BaseValidator             For Each Validator in Validators                Message.Text &= Validator.ID & " error message: "                Message.Text &= Validator.ErrorMessage & "<br/>"             Next               End Sub       </script>    </head> <body>    <form runat="server">       Phone: <asp:textbox  runat="server"/>       <asp:requiredfieldvalidator                     controltovalidate="phone"          display="dynamic"          errormessage="Required!"          runat="server"/>       <asp:regularexpressionvalidator                     controltovalidate="phone"          display="dynamic"          validationexpression="^[2-9]\d{2}-\d{3}-\d{4}$"          errormessage="Enter a phone number in the form xxx-xxx-xxxx"              runat="server"/>       <br/>       <asp:button  text="Submit" runat="server"/>    </form>    <br/>    <asp:label  runat="server"/> </body> </html>

Notes

Because we are displaying only properties from the validator controls that are inherited from the BaseValidator control (from which all validation controls are derived), we don't need to cast the validator to its specific type before accessing the properties. If, however, we wanted to display a property that was specific to the type of validator used (such as the ValidationExpression property of the RegularExpressionValidator class), we would need to cast the control to the correct type. In Visual Basic .NET, this is done using the CType keyword.