+TCallback provides a basic callback handler that can be invoked from the +client side by using the javascript ojbect obtained from the +ActiveControl.Javascript property. +You can set the CallbackParameter property from javascript directly on +the object returned by ActiveControl.Javascript. +Once you are ready, you can call the dispatch() method on the object to +execute the callback. +The server-side event OnCallback is raised when a callback is requested made. +
+ ++Example usage: +
++TEventTriggeredCallback triggers a new callback request when a particular EventName +on a control with ID given by ControlID is raised. +The default action of the event on the client-side can be prevented when +PreventDefaultAction is set to true. +
+ +The following classes provide the basic infrastructure classes required to -realize the active controls.
+realize the active controls. They can be useful to develop new active controls, but Prado users tipically don't need +to use them.+ TActiveControlAdapter customizes the parent TControl class for active control classes. + It tracks changes in the viewstate values of the control and update + differences of the client-side HTML element attributes. +
++ TActiveListControlAdapter allows the adapted list controls to change the selections + on the client-side during a callback request. +
+ TActivePageAdapter process the page life-cycle for callback requests. +
+ TBaseActiveControl class provided additional basic properties common for every + active control. An instance of TBaseActiveControl or its decendent + TBaseActiveCallbackControl is created by TActiveControlAdapter::getBaseActiveControl() + method. + The EnableUpdate property determines wether the active + control is allowed to update the contents of the client-side when the callback + response returns. +
+ TCallbackResponseAdapter alters the THttpResponse's outputs. + A TCallbackResponseWriter is used instead of the TTextWrite when + createHtmlWriter is called. Each call to createHtmlWriter will create + a new TCallbackResponseWriter. When flushContent() is called each + instance of TCallbackResponseWriter's content is flushed. + The callback response data can be set using the ResponseData property. +
The following classes provide advanced properties and events needed to realize the active controls. +A Prado user can use them to customize active controls behaviour and interact directly with the client side during a callback. +
+| +An active label text being set as the result of a callback: + |
+
+ Click Me!
+ |
| +A TCallback with a 3-items array as parameter. +The first parameter is defined in the onclick() attribute of the red div; +The second parameter is defined in the body of the javascript function; +The third parameter is taken from the textbox; + |
+
+ Click Me!
+Parameter 1 is Parameter 2 is Parameter 3 is |
| + A callback will be executed when the textbox receives and loses focus + |
+ |
| +A timer updating a label with the current time every 5 seconds: + |
+ |
| + A callback will be executed when the textbox text changes + |
+ |
+TTimeTriggeredCallback sends callback request every Interval seconds. +Upon each callback request, the OnCallback event is raised. +The timer can be started by calling startTimer() and stopped using +stopTimer(). The timer can be automatically started when +StartTimerOnLoad is true. +
+ ++TValueTriggeredCallback observes the value with PropertyName of a +control with ControlID. Changes to the observed +property value will trigger a new callback request. The property value is checked +for changes every Interval seconds. +A DecayRate can be set to increase the polling +interval linearly if no changes are observed. Once a change is +observed, the polling interval is reset to the original value. +
+ +