[Dynapi-Help] 'e' help....Thanks!

James Musick Fri, 12 Jul 2002 08:52:51 -0700


  Thanks everyone for the detailed explanations and pointers to the relevant 
areas in dynapi.js, etc.
  Makes more sense to me.


  Cheers,
  James

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--- Begin Message --- At 2002-07-12 00:17, James Musick wrote:

I think the problem is that I didn't/don't understand when things are being called and/or triggered by DynAPI.

For example:
File A:
anObj= new myObject();
.....other stuff
DynAPI.document.addChild(anObj);
---------
File B:
function myObject()
{
this.field1=null;this.field2=null;
var l = new EventListener(this);
l.oncreate = function(e)
{var o = e.getTarget();}
}

[snip]

So the way I'm currently thinking of it (and this may *still* be confused...so please correct me/add to the info if possible) is that the above code will
1. Create an instance of myObject called anObj.

Yes. But as written above its superclass is the generic Object in javascript, not a DynObject.

2. Part of this object is an EventListener

The object has an empty array of EventListeners as a property (dynapi.js)

3. somehow/somewhere the oncreate() function of the event listener is called inside of DynAPI.document.addChild()

The addChild method in dyndocument.js calls the addChild method in dynapi.js for the DynObject.

DynObject.prototype.addChild = function(c) {
        if(c.isChild) c.parent.removeChild(c);
        c.isChild = true;
        c.parent = this;
        if(this.created) c.create()                     // <- Step one
        this.children[this.children.length] = c;
        return c;
};
DynObject.prototype.create = function() {
        this.flagPrecreate();
        this.specificCreate();
        this.created = true;
        var l = this.children.length;
        for(var i=0;i<l;i++) this.children[i].create()
        this.invokeEvent("create");                     // <- This is the one you're looking for
};

4. That call of oncreate is passing a reference of the event 'e' that triggered the 'oncreate' call.

DynObject.prototype.invokeEvent=function(type,e,args) {
        if (!e) e=new DynEvent(type,this);
        if (this.hasEventListeners) for(var i=0;i<this.eventListeners.length;i++) {
                e.target=this.eventListeners[i].target;
                this.eventListeners[i].handleEvent(type,e,args);
        }
        ...
}

EventListener.prototype.handleEvent=function(type,e,args) {
        if(this["on"+type]) this["on"+type](e,args);
};

As the call to invokeEvent didn't provide the e argument a new DynEvent is created, with the current object as its source.

5. e.getTarget() returns the object that triggered it all in the beginning.

In effect yes, but getTarget simply returns the "target" property of the event. It gets a little messier if the event bubbles... or quite powerful if you set up the listener in a different way.

You could for example have a list where the listener for the items in the list has the list they will be attached to as their target.

To complicate matters: there is a getSource method too... That one should be the one that triggered it.

3,4,5 are still pretty speculative since I didn't see code doing that specifically.
But the addChild() must be triggering the oncreate event somehow, but I'm not sure how/why.
You could have multiple Event listeners with a single object, certainly. If you did an addChild() I guess it seems that an event is firing (perhaps of a type that is a creation event) and so all the EventListeners that are associated with the object (only 'l' in this case) execute their oncreate function.

I think what was confusing me was that when you create an instance of the object you're not really triggering the oncreate() function. That seems to happen when you do Dynapi.document.addChild().

Is this roughly correct?

Roughly. The oncreate is called after the browser element has been created (a "div" most often). If you are addChild()ing to an object that hasn't been created yet the oncreate() isn't called at that time. It will be called when the parent becomes part of the document though.

Please note that DynAPI.document isn't the standard "document" object but a DynDocument.

Thanks, by the way, for the discussion/help.

Cheers,
James

You're welcome!

/Lunna
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[Dynapi-Help] 'e' help....Thanks!

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