Macromedia flex 2 Manuale

42

Creating Custom Events

eventObj.isEnabled=true;
dispatchEvent(eventObj);

For complete examples that create and dispatch custom events, see 

 and 

.

Creating static constants for the Event.type property

The constructor of an event class typically takes a single required argument that specifies the 
value of the event object’s 

type

 property. In the previous section, you passed the string 

enableChange

 to the constructor, as the following example shows:

// Define event object, initialize it, then dispatch it. 
var eventObj:EnableChangeEvent = new EnableChangeEvent("enableChange");
dispatchEvent(eventObj);

The Flex compiler does not examine the string passed to the constructor to determine if it is 
valid. Therefore, the following code compiles, even though 

enableChangeAgain

 might not 

be a valid value for the 

type

 property:

var eventObj:EnableChangeEvent = 

new EnableChangeEvent("enableChangeAgain");

Because the compiler does not check the value of the 

type

 property, the only time that your 

application can determine if 

enableChangeAgain

 is valid is at run time. 

However, to ensure that the value of the 

type

 property is valid at compile time, Flex event 

classes define static constants for the possible values for the 

type

 property. For example, the 

Flex 

EffectEvent

 class defines the following static constant:

// Define static constant for event type.
public static const EFFECT_END:String = "effectEnd";

To create an instance of an EffectEvent class, you use the following constructor:

var eventObj:EffectEvent = new EffectEvent(EffectEvent.EFFECT_END);

If you incorrectly reference the constant in the constructor, the compiler generates a syntax 
error because it cannot locate the associated constant. For example, the following constructor 
generates a syntax error at compile time because 

MY_EFFECT_END

 is not a predefined constant 

of the EffectEvent class:

var eventObj:EffectEvent = new EffectEvent(EffectEvent.MY_EFFECT_END);