Some DevExpress MVC extensions can work in callback mode by requesting the server via their own callbacks. Using callbacks is an efficient way to load/update extension content on demand (to minimize the initial data transfer) or to perform some lengthy functional operations (such as file uploads).
The following requirements should be met for an extension that is used in callback mode.
An extension should be defined in a separate Partial View (.cshtml or .vbhtml).
It is required that a Partial View contains only the extension definition code, without any additional markup.
A Controller should contain an additional Action method to handle extension callbacks and route them directly to a Partial View containing the extension. This allows the extension render to be conditionally updated in response to the end-user action performed.
Callback routing logic should be defined using a CallbackRouteValues property of an extension's settings object. This property allows the names of the callback handling Controller and Action to be specified.
Note that these requirements are not required for all extensions that support the use of callbacks. For instance, the UploadControl extension might not be declared within a Partial View - it is enough for it to properly implement a callback handler Action method and reference this method in the CallbackRouteValues property's value.
Extensions That Can Use Callbacks
The table below lists DevExpress MVC extensions that support the use of callbacks.