System.Web 2.0.0.0 System.Web.UI.WebControls.WebParts.ConnectionPoint

In every Web Parts connection between two server controls, each control must have (among other requirements) an associated connection point object that enables it to connect to the other control and to either provide or consume data, depending on whether the control is designated as the provider or consumer for the connection. A object in general contains the details for how a control can connect to another control and the type of data it can share. For a control acting as the provider in a connection, its connection point must be a object. For details on Web Parts connections and connection points, see the topics listed in the See Also section below.

To create a object, several steps are required:

Create an interface. When a provider shares data with a consumer, it does so by getting an instance of an interface, and returning that instance to a consumer.

Implement the interface in a provider. A or other server control (any type of server control in a zone can be used) that will be the provider must implement the interface created in the first step.

Identify a callback method. A method in the provider must be identified as the callback method to establish a connection. This method returns an instance of the implemented interface to a consumer. The Web Parts approach for identifying a callback method in the provider is to add a ConnectionProvider metadata attribute (defined by the class) to the method that returns the interface instance. When the attribute is added, the only required parameter is a display name to use for the provider connection point. Optional parameters can also be added, such as an ID for the connection point.

After a control has been equipped to act as a provider, the control can participate in connections (assuming that a consumer control is similarly equipped and available). To create a static, declarative connection in the markup of a Web page, developers can use the <asp:webpartconnection> element. If the ConnectionProvider attribute in the provider source code that identifies the callback method specifies an ID for the connection point, then that value must be assigned to the ProviderConnectionPointID attribute in the <asp:webpartconnection> element on a page. One reason that a developer might specify an ID for a provider connection point is if there are multiple connection points in the provider control. If an ID is not specified for the provider connection point in the provider control, a value does not have to be assigned to the ProviderConnectionPointID attribute in the page either, because the connection will be created using a default value obtained from the field.

To create a connection in code, developers must create a new object by calling the method and passing to it the ID of the provider control, along with the ID or index of the defined object in the provider control. The returned object, along with a reference to the provider control, a reference to the consumer control, and a corresponding object, are all passed to the method to create a new object.

Although developers can use provider connection points as part of establishing connections either declaratively or programmatically, users can also interact with provider connection points to establish connections through the user interface (UI). If developers declare a control on a Web page, it provides a run-time UI for users to create connections. If users choose the consumer control as the starting point for establishing the connection by clicking its connect verb (they could also choose the provider; there is no difference in the resulting connection), in the UI they will see a drop-down list control with the display name of the available provider connection point (or points if there are multiple ones). Users must select a provider connection point to create a connection.

A object associates directly with a specific provider control, and stores details about a connection in the properties it inherits from the base class. For example, in the inherited property, a provider connection point keeps the type of interface returned by the provider. If the provider and consumer in a connection both work with the same interface type, the controls are compatible and capable of forming a direct connection. If the provider and consumer cannot work with the same interface type, they are incompatible and must use a object to translate the provider connection point's value into a type that the consumer can work with. Another important inherited property is the property, which provides a friendly name to display in the UI for users to choose a provider connection point when creating connections. The display name is the required parameter when developers add a ConnectionProvider attribute to the callback method in a provider control. The inherited property is also useful, as indicated above, because it provides a unique identifier for a provider connection point in the event that a provider has multiple connection points. A provider can have multiple objects defined in it, and in this case, when developers add the ConnectionProvider attribute to a method, they should specify an ID value to distinguish each connection point. One other notable inherited property is the property, which indicates whether a provider connection point can connect simultaneously to multiple consumers. This property value is true by default for provider connection points (whereas it defaults to false for consumer connection points).

The class adds several unique methods to the members it inherits from the class. The method retrieves an instance of the interface that the callback method will return to consumers. The method retrieves additional consumer interfaces that are part of an existing connection, but are not the interfaces used to establish the connection.

Defines a connection point object that enables a server control acting as a provider to form a connection with a consumer.

- Constructor
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  The constructor for the class simply calls the base constructor, passing to it the various parameters and initializing the base class.

  The base class constructor checks a number of the parameters for a connection point and can throw several exceptions. For a list of possible exceptions, see the Exceptions section.

  You can call the constructor to create your own instance of the class. However, in cases where you are simply establishing a connection and not extending the class, you should call the method to return an existing connection point object from a provider.

  Initializes a new instance of the class.

  A unique identifier for the provider connection point.
  2.0.0.0
- Method
  System.Object ``

  This method returns an object from the provider control that is an instance of the interface used to establish a connection. The type of the object will be the type of the implemented interface. For example, two interfaces that are implemented for connections in the Web Parts control set are and . When the method is called on a object, if the associated provider implements one of these interfaces, the returned object will be of the same type.

  The method is called by objects when a connection is being activated. This is a critical step that actually initiates a connection and begins the process that enables two controls to share data.

  The consumer control in a connection must be able to work with the same type of interface as the provider. If it does not, the controls are incompatible and a object must be used to establish a connection.

  Invokes the callback method in a provider control that gets an interface instance to return to consumers.

  An that is an instance of the interface a provider returns to consumers to establish a connection.

  The control acting as the provider in a Web Parts connection. 2.0.0.0
- Method
  System.Web.UI.WebControls.WebParts.ConnectionInterfaceCollection ``

  A provider connection point object always has a default interface that is used to establish a connection with consumers. An instance of the default interface is retrieved by calling the method on a object.

  However, some provider controls will implement multiple interfaces to provide to consumers as part of a connection. These interfaces, which are not the default ones used to establish a connection, are called secondary interfaces. The method provides a way to return a collection of references to the secondary interfaces, just as the method returns a reference to the default interface.

  Gets an optional collection of secondary interfaces that can be supported by a provider connection point.

  A of additional interfaces provided by the control acting as a provider.

  The control acting as the provider in a Web Parts connection. 2.0.0.0