Generate event handlers

Applications built with Flex are event-driven. User interface components respond to various events, such as a user clicking a button or the initialization of an object is complete. You write event handlers in ActionScript code that define how the component responds to the event.

Note: You can also generate event handlers for non-visible items such as RemoteObject and HTTPService.

Flash Builder provides event handler assistance that generates the event handler functions for a component. Within the generated function, you write the code that defines the component behavior in response to the event.

Content assist for an item in the MXML editor lets you access event handler assistance.

About generated event handlers

When Flash Builder generates an event handler function, it places the event handler in the first Script block of the file. The function is placed at the end of the Script block. The generated event handler has protected access and accepts the appropriate subclass of Event as its only parameter.

Flash Builder generates a unique name for the event handler based on the component’s class name or a custom name for the event handler that you specify. If you do not specify a custom name, the name is generated according to the following process:

  • If an id property is defined, Flash Builder bases the name on the id property.

  • If there is no id property defined for the component, Flash Builder generates a unique name, based on the component’s class name.

You provide the body of the event handler. The following code block shows a generated event handler for a Button.

. . . 
        protected function myButton_clickHandler(event:MouseEvent):void 
            // TODO Auto-generated method stub 
<s:Button label="Button" id="myButton" click="myButton_clickHandler(event)"/> 
. . .

Flash Builder designates a default event for each user interface component. For example, the default event for a Button is the click event.

Generating event handlers for components

  1. In an MXML block in the editor, create a component, but do not specify any events.

  2. Enable content assist for the properties of a component by typing a space after the class name.

  3. From the list of selected properties, select an event (for example, doubleClick).

  4. Press Control+Space and select Generate Event Handler.

    Flash Builder generates a unique name for the event handler and places the event handler in the Script block.

    Note: If you specify a custom name for the event handler, then Flash Builder cannot generate the handler. If you want to use a custom name, first generate an event handler and then modify the name of the handler in both the event property and the generated handler.

    Add the code for your implementation of the event handler to the generated event handler function.