ClientScriptManager::GetCallbackEventReference Method (Control, String, String, String)
Obtains a reference to a client function that, when invoked, initiates a client call back to a server event. The client function for this overloaded method includes a specified control, argument, client script, and context.
Assembly: System.Web (in System.Web.dll)
public:
String^ GetCallbackEventReference(
Control^ control,
String^ argument,
String^ clientCallback,
String^ context
)
Parameters
- control
- Type: System.Web.UI::Control
The server Control that handles the client callback. The control must implement the ICallbackEventHandler interface and provide a RaiseCallbackEvent method.
- argument
- Type: System::String
An argument passed from the client script to the server
RaiseCallbackEvent method.
- clientCallback
- Type: System::String
The name of the client event handler that receives the result of the successful server event.
- context
- Type: System::String
Client script that is evaluated on the client prior to initiating the callback. The result of the script is passed back to the client event handler.
| Exception | Condition |
|---|---|
| ArgumentNullException | The Control specified is nullptr. |
| InvalidOperationException | The Control specified does not implement the ICallbackEventHandler interface. |
The GetCallbackEventReference(Control, String, String, String) method performs an out-of-band callback to the server that is a modified version of a page's normal life cycle. For more information, see Implementing Client Callbacks Programmatically Without Postbacks in ASP.NET Web Pages.
Note |
|---|
When the browser is Microsoft Internet Explorer (version 5.0 or later), the script callback mechanism is implemented through the Microsoft.XmlHttp COM object and requires the browser to be set to run ActiveX controls. For other browsers, an XMLHttpRequest using the browser's local Document Object Model (DOM) is used. To check whether a browser supports client callbacks, use the SupportsCallback property. To check whether a browser supports XML over HTTP, use the SupportsXmlHttp property. Both properties are accessible through the Browser property of the intrinsic ASP.NET Request object. |
The GetCallbackEventReference overload of the GetCallbackEventReference method performs a callback synchronously using XML over HTTP. When sending data synchronously in a callback scenario, synchronous callbacks return immediately and do not block the browser. No two synchronous callbacks callback can execute at the same time in the browser. If a second synchronous callback is fired while one is currently pending, the second synchronous callback cancels the first and only the second callback will return.
To send data asynchronously, use one of the overloads that takes the useAsync parameter, which is a Boolean value controlling this behavior. In the asynchronous scenario you can have multiple pending callbacks; however, the order in which they return is not guaranteed to match the order in which they were initiated.
Additionally, this overload of the GetCallbackEventReference method specifies no client function to handle the case of an error condition generated by the RaiseCallbackEvent method. To specify a client error callback handler, use one of the overloads that takes the clientErrorCallback parameter.
The GetCallbackEventReference(Control, String, String, String) method takes an optional string argument parameter and returns a string. To pass in or to receive multiple values, concatenate values in the input or return string, respectively.
Note |
|---|
Avoid using the view state in the implementation of page or control properties that need be updated during script callback operations. If the properties are to survive page requests, you can use session state. |
The following code example demonstrates how to use two overloads of the GetCallbackEventReference method in a client callback scenario that increments integers.
Two callback mechanisms are shown; the difference between them is the use of the context parameter. A ReceiveServerData1 client callback function is provided using the context parameter. In contrast, the ReceiveServerData2 client callback function is defined in a <script> block on the page. A RaiseCallbackEvent method is the server handler that increments the value that is passed to it and the GetCallbackResult method returns the incremented value as a string. If the RaiseCallbackEvent method returns an error, then the ProcessCallBackError client function is called.
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Note