I have a class that creates a button and connects a listener to the click event. In a sub class I'd like to replace the superclass handler. This code adds a listener:
row.query("[value='Save']").onClick.listen(handleNewAlert);
How do I remove the existing listener?
The Stream.listen() method returns a StreamSubscription object. Call StreamSubscription.cancel() to cancel the event listener.
var subs = element.onClick.listen((e) => print(e));
// Remove the listener.
subs.cancel();
// Add another listener.
element.onClick.listen((e) => print(e));
See this article for more information.
Greg's answer describes how to unsubscribe from the event source.
This is correct, but IMO a bit awkward, as you need to keep the subscription instance around in case that any derived class wants to cancel it, or you need to provide a method for this on the base class if you want to hide the details.
As you say that you want to replace the handler, which I understand as providing a different implementation, a simpler approach is to simlpy override handleNewAlert method in the derived class.
Of course, it won't work if instead of method name you have specified an anonymous function, as it obviously can't be overridden, but in the scenario shown in your example, this might be an easier approach.
Related
I have Problem with onTick() method, I have two buttons for two different situations, in each one I will load separate dataSource, just like the czml.html example on Sandcastle. I have two different definition for onTick() method for each button seperately, to do some specific things when we reach at a specific time. In the reset method I am removing entities and dataSources of my viewer, but I cannot remove onTick method implementation.
When I am running my code, the default button is doing perfectly fine, but when I press other button, all those conditions that I mentioned for the first button is also happening at the same time, and it will not let my second onTick method to perform its job correctly. Do you know how I can deactivate the first onTick method?
Take a look at the addEventListener documentation, you'll find two different ways to undo the addition of an event listener: One is to call the matching removeEventListener, and the other is to save the return value from addEventListener and invoke it later.
Here's some code showing both ways. Use whichever option makes more sense for your code, but don't use both at once.
function onTickCallback(clock) {
// ... do stuff with every tick ...
}
var unsubscribeTicks = viewer.clock.onTick.addEventListener(onTickCallback);
function unsubscribeOption1() {
// One option is to call removeEventListener. In this case, you
// don't need to save "var unsubscribeTicks" at all, but you do
// need a reference to the original onTickCallback.
viewer.clock.onTick.removeEventListener(onTickCallback);
}
function unsubscribeOption2() {
// The other option is to save the return value of addEventListener,
// and later invoke it. This could be a cleaner option if the
// onTickCallback was declared anonymously inline.
unsubscribeTicks();
}
I am using GWT textbox.
Whenever textbox.setText() method is called, i want to perform an action in some other class.
ValueChangeEvent is not fired whenever setText() is called.
Is there any event that will be fired or any ways to achieve this?
Please help
You could try to use setValue(String value, boolean fireEvent) method
If you have a look at the TextBox.seText() method, you'll see that, all the way down to the actual DOM, no event is ever generated, so what you want to do simply won't work off-the-box.
I see two options:
Whenever you call setText, you also call the event handler of your choice or, much better
Make your own TextBox that extends TextBox, and override the setText() method so that it first calls super.setText() and then does whatever event generation you'd like
I feel the way inner components could be accessed be better than what I know.
I know we can access any inner component something like:
FlexGlobals.topLevelApplication.someChild1.someChild2.someChild3… and so on
I've a components which has number of parent components hierarchy. I wish to know if there could be anyway I could access the last child without referring all of its parent.
I need to trigger an event on that component.
FlexGlobals.topLevelApplication.child1.child2.child3.dispatchEvent(new Event('clearData', true));
Updated: I tried the way you suggested in point 1. I've added the event listener on child component and try to dispatch it from a action script file, but it went unheared.\
child3.addEventLisener('clearData', clearHandler);
And then I dispatched the event some thing like:
dispatchEvent(new Event(modelApp.CLEAR_PALETTE, true)
try to add
FlexGlobals.topLevelApplication.systemManger.addEventLisener('clearData', clearHandler);
in child3
and dispacthed it from any where you want,
for dispatching use the following
FlexGlobals.topLevelApplication.systemManager.dispatchEvent(new Event(modelApp.CLEAR_PALETTE, true)
How I understood from the question used no good principles of application design, but that's another question.
In your case, you can use stage as global currentTarget for bubbles events. Dispatch event from displayObject with bubbles = true; In target display object listen event with stage object with/out capture phase.
in any displayObject:
dispatchEvent(new Event("myEvent", true));
in target displayObject:
// add ADDED_TO_STAGE event listener in constructor or when component creation complete
protected function component_creationCompleteHandler(event:FlexEvent):void
{
addEventListener(Event.ADDED_TO_STAGE, onAddToStage);
}
..
protected function onAddToStage(event:Event):void
{
stage.addEventListener("myEvent", eventHandler, true);
}
protected function eventHandler(event:Event):void
{
trace("eventHandler");
}
It is better than use reference to FlexGlobals object. Code more flexible.
I think you should go down to the level of component and addEventListener on initialize.
and dispatch from where ever you want.
other way is to do that, you need to save component reference(ID) in object on creationComplete. save its refence in your model. now you can access it where ever you want. and do what ever you want.
i also did in this way, i saved my screen components refrence in an array and access it where i need to dynamically validate all components.
otherwise you need nested looping to got your required child.
I'm currently working on a project that involve a re-implementation of the Array class.
This object needs to be an Array for compatibility reasons, while I also need to keep control of what is written in.
I cannot seem to find any way to check property creation inside of a dynamic object in AS3. Something that would work like the Event.ADDED_TO_STAGE but, like, ClassEvent.PROPERTY_ADDED.
I override methods like push, splice etc, but I cannot control direct assignation : MyArray[i] = ...
Is such a thing even possible ?
Of course, I could make some kind of validations elsewhere, but this would involve accessing a part of the code I cannot modify.
Thanks for your time !
I'm not sure I follow you entirely but you may be looking for the Proxy class:
http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/utils/Proxy.html
An example at the bottom shows you how you can override direct assignment:
override flash_proxy function setProperty(name:*, value:*):void {
_item[name] = value;
}
Using this you would be able to dispatch a custom event that would be fired any time an item was added to your ProxyArray
I'm still trying to get my head around the best way to structure event flows. Someone made a lot of sense by telling me that contained objects should be decoupled from their parent containers so they're reusable between containers. Instead of calling their parent's function, they dispatch an event. Sensible!
I recently myself in the awkward-feeling situation of dispatching an event on a contained object, from its parent. It seems more intuitive for an object to be the one dispatching its own events. Maybe I'm bordering on breaking the Law of Demeter?
Example of what I'm doing:
child.dispatchEvent(new ChildEvent(ChildEvent.IM_BEING_A_CHILD));
Am I correct in feeling strange here, or is it a normal thing for one object to dispatch another object's events?
You are not necessarily breaking any rules here - if dispatchEvent is a public function then you are allowed to call it from anywhere you like.
If you want to keep things cleaner from an encapsulation point of view you could instead expose an explicit function that the parent can call for a particular event to occur - eg:
child.doSomeChildAction();
and on the child class:
public function doSomeChildAction():void
{
dispatchEvent(new ChildEvent(ChildEvent.IM_BEING_A_CHILD));
}
This way if you need to change the way child sends the event, what kind of event is sent, or what actions occur when the child sends the event it is all encapsulated in the child class, and so will be easier to manage.