Assembly: System.Web (in system.web.dll)
This interface is designed to be used with Web Parts connections. In a Web Parts connection, two server controls that reside in a WebPartZoneBase zone establish a connection and share data, with one control acting as the consumer and the other control acting as a provider. The mechanism for sharing data in a Web Parts connection is an interface instance, which the provider serves to the consumer by means of a callback method. To establish a connection, the consumer and provider must both work with the same interface type for sharing data. If the consumer does not recognize the interface type sent by the provider, it is still possible to connect the controls by means of a transformer (a WebPartTransformer object) that translates the interface instance sent by the provider into a type that the consumer recognizes. For details on connections, see WebPartConnection and Web Parts Connections Overview.
The IWebPartField interface is a provider interface included with the Web Parts control set as a standard interface for creating connections based on a data field. You can also create custom interfaces to use with Web Parts connections, but in many data-driven Web applications, it is useful to create connections based on a common row (for details, see the IWebPartRow interface), table (for details, see the IWebPartTable interface), or field from the data source, using the IWebPartField interface. In a typical connection, a WebPart control acting as a provider would implement the IWebPartField interface and provide an instance of the interface to consumers in a special callback method. For example, the provider might implement an IWebPartField interface for a field in your user information table that contains a Web user's postal code data. Another WebPart control acting as a consumer would define a special method to receive the interface instance, and could then extract the postal code data, and look up and display weather information based on the postal code.
The IWebPartField interface has two exposed members. The Schema property returns schema information about the data field encapsulated in a PropertyDescriptor object. The GetFieldValue method declares a method that an implementer (such as a provider control) uses to retrieve the interface instance's field data when the callback method is invoked.
The following code example demonstrates how to create a static connection between two controls using the IWebPartField interface. The code example has three parts:
Source code for two custom WebPart controls that can form a connection using the IWebPartField interface, with one control acting as the provider, the other acting as the consumer.
A Web page that hosts the controls and declares the static connection in persistence format.
A description of what happens when the example code runs.
The first part of the code example is the source code for the two custom controls. First is the code for the provider, which implements the IWebPartField interface. For simplicity in the example, the provider creates a table with some data rather than connecting to a database. The GetConnectionInterface method serves as the provider's connection point, the callback method that returns the interface instance to the consumer. As for the consumer, it retrieves the interface instance from the provider in its method named SetConnectionInterface, which is marked with a ConnectionConsumer attribute. After retrieving the instance of the interface, the consumer, in its OnPreRender method, calls the implementation of the GetFieldValue method in the provider, to retrieve the actual data.
For the code example to run, you must compile this source code. You can compile it explicitly and put the resulting assembly in your Web site's Bin folder or the global assembly cache. Alternatively, you can put the source code in your site's App_Code folder, where it will be dynamically compiled at run time. This code example uses dynamic compilation. For a walkthrough that demonstrates how to compile, see Walkthrough: Developing and Using a Custom Server Control.
Imports System Imports System.Collections Imports System.ComponentModel Imports System.Data Imports System.Reflection Imports System.Security.Permissions Imports System.Web Imports System.Web.UI Imports System.Web.UI.WebControls Imports System.Web.UI.WebControls.WebParts Namespace Samples.AspNet.VB.Controls ' This sample code creates a Web Parts control that acts as a ' provider of field data. <AspNetHostingPermission(SecurityAction.Demand, _ Level:=AspNetHostingPermissionLevel.Minimal)> _ <AspNetHostingPermission(SecurityAction.InheritanceDemand, _ Level:=AspNetHostingPermissionLevel.Minimal)> _ Public NotInheritable Class FieldProviderWebPart Inherits WebPart Implements IWebPartField Private _table As DataTable Public Sub New() _table = New DataTable() Dim col As New DataColumn() col.DataType = GetType(String) col.ColumnName = "Name" _table.Columns.Add(col) col = New DataColumn() col.DataType = GetType(String) col.ColumnName = "Address" _table.Columns.Add(col) col = New DataColumn() col.DataType = GetType(Integer) col.ColumnName = "ZIP Code" _table.Columns.Add(col) Dim row As DataRow = _table.NewRow() row("Name") = "John Q. Public" row("Address") = "123 Main Street" row("ZIP Code") = 98000 _table.Rows.Add(row) End Sub <ConnectionProvider("FieldProvider")> _ Public Function GetConnectionInterface() As IWebPartField Return New FieldProviderWebPart() End Function Public ReadOnly Property Schema() As ComponentModel.PropertyDescriptor _ Implements IWebPartField.Schema Get ' The two parameters are row and field. Zero is the first record. ' 0,2 returns the zip code field value. Return TypeDescriptor.GetProperties(_table.DefaultView(0))(2) End Get End Property Sub GetFieldValue(ByVal callback As FieldCallback) _ Implements IWebPartField.GetFieldValue callback(Schema.GetValue(_table.DefaultView(0))) End Sub End Class 'FieldProviderWebPart ' This sample code creates a Web Parts control that acts as a ' consumer of an IWebPartField interface. <AspNetHostingPermission(SecurityAction.Demand, _ Level:=AspNetHostingPermissionLevel.Minimal)> _ <AspNetHostingPermission(SecurityAction.InheritanceDemand, _ Level:=AspNetHostingPermissionLevel.Minimal)> _ Public Class FieldConsumerWebPart Inherits WebPart Private _provider As IWebPartField Private _fieldValue As Object Private Sub GetFieldValue(ByVal fieldValue As Object) _fieldValue = fieldValue End Sub Public Property ConnectionPointEnabled() As Boolean Get Dim o As Object = ViewState("ConnectionPointEnabled") Return IIf(Not (o Is Nothing), CBool(o), True) End Get Set(ByVal value As Boolean) ViewState("ConnectionPointEnabled") = value End Set End Property Protected Overrides Sub OnPreRender(ByVal e As EventArgs) If Not (_provider Is Nothing) Then _provider.GetFieldValue(New FieldCallback(AddressOf GetFieldValue)) End If MyBase.OnPreRender(e) End Sub Protected Overrides Sub RenderContents(ByVal writer As _ HtmlTextWriter) If Not (_provider Is Nothing) Then Dim prop As PropertyDescriptor = _provider.Schema If Not (prop Is Nothing) AndAlso Not (_fieldValue Is Nothing) Then writer.Write(prop.DisplayName & ": " & _fieldValue) Else writer.Write("No data") End If Else writer.Write("Not connected") End If End Sub <ConnectionConsumer("FieldConsumer", "Connpoint1", _ GetType(FieldConsumerConnectionPoint), AllowsMultipleConnections:=True)> _ Public Sub SetConnectionInterface(ByVal provider As IWebPartField) _provider = provider End Sub End Class 'FieldConsumerWebPart Public Class FieldConsumerConnectionPoint Inherits ConsumerConnectionPoint Public Sub New(ByVal callbackMethod As MethodInfo, _ ByVal interfaceType As Type, ByVal controlType As Type, _ ByVal name As String, ByVal id As String, _ ByVal allowsMultipleConnections As Boolean) MyBase.New(callbackMethod, interfaceType, controlType, _ name, id, allowsMultipleConnections) End Sub Public Overrides Function GetEnabled(ByVal control As Control) _ As Boolean Return CType(control, FieldConsumerWebPart).ConnectionPointEnabled End Function End Class 'FieldConsumerConnectionPoint End Namespace ' Samples.AspNet.VB.Controls
The second part of the code example is the Web page that declares the static connection and hosts the controls. Near the top of the page is a Register directive that declares the namespace of the source code contained in the App_Code directory. The connection is declared using an <asp:webpartconnection> element. The custom consumer and provider controls are declared in a <zonetemplate> element within an <asp:webpartzone> element, which is required for them to be able to connect (they must reside within a zone that inherits from the WebPartZoneBase class).
<%@ page language="VB" debug="true" %> <%@ Register tagprefix="IField" Namespace="Samples.AspNet.VB.Controls" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <!-- This code sample creates a page with two Web Parts controls and establishes a connection between the controls. --> <script runat="server"> </script> <html xmlns="http://www.w3.org/1999/xhtml" > <head runat="server"> <title>IWebPartField Test Page</title> </head> <body> <form id="form1" runat="server"> <div> <asp:webpartmanager id="WebPartManager1" runat="server"> <StaticConnections> <asp:WebPartConnection id="con1" ProviderID="provider1" ConsumerID="consumer1" ConsumerConnectionPointID="Connpoint1"> </asp:WebPartConnection> </StaticConnections> </asp:webpartmanager> <asp:webpartzone id="WebPartZone1" runat="server"> <zoneTemplate> <ifield:fieldproviderwebpart runat="Server" ID="provider1" Title="Provider" /> <ifield:fieldconsumerwebpart runat="Server" ID="consumer1" Title="Consumer"/> </zoneTemplate> </asp:webpartzone> </div> </form> </body> </html>
Load the page in a browser. The consumer control displays the data provided from the specified field, which the provider makes available through an instance of the IWebPartField interface.
Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.