MACROMEDIA FLEX 2-MIGRATING APPLICATIONS TO FLEX 2 Manual do Utilizador descarregar pdf (Página 114)

114 Events

If you try to call another method on the target (for example, the getStyle() method), Flex

returns an error. The

getStyle() method is a method of UIComponent, a subclass of

DisplayObject. Therefore, you must cast event.target to UIComponent before calling the

getStyle() method, as the following example shows:

function myEventListener(e:Event) {

UIComponent(e.target).getStyle("color");

}

If you use the target property of the Event object to determine which control triggered the

event, you should consider changing the

target property to currentTarget. The

currentTarget property supports event bubbling and capturing, which are new in Flex 2.

During these phases, the event is actually being handled by the target’s parent containers. The

target still refers to the dispatcher of the event, but the

currentTarget refers to whatever

control is currently processing a bubbling or capture event.

For example, if you have

<mx:List click="..."/>, inside the click handler event.target

might be one of the rows, but

event.currentTarget is a reference to the List control, which

is generally what you would expect.

Another example is what occurs when you assign a mouseDown handler on a TextInput

control. Actually, the TextField class that is inside the TextInput control dispatches the event

(depending on where the user clicked), so the TextField control, not the TextInput control, is

the

target. However, the TextInput control is the currentTarget if that is where you

attached the handler.

Most controls have internal subcomponents that are often the target for mouse events.

Using static constants

Use static constants to represent event types; for example, use MouseEvent.CLICK rather than

"click", as the following example shows:

addEventListener("click", myClickListener); // Flex 1.5

addEventListener(MouseEvent.CLICK, myClickListener); // Flex 2

Change the following:

switch (event.type) {

case "click":

...

}

To this :

switch (event.type) {

case MouseEvent.CLICK:

...

}

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