How to link “extent-change” and “update-end” events in Dojo?

问题

In ArcGIS JS API I need to trigger a method of my class when the processing after an extent change is complete. I didn't find any special event for this. extent-change triggers too early, when the data are not loaded yet. update-end is triggered also by the function I want to call, making an endless loop. So what I need is to link the two events together, the second one just once. But how?

Most of my events look like this:

this.events.push(on(this.map, "extent-change", lang.hitch(this, this._foo)));

This is not suitable for event linking, so I need to make the linked event some other way. What I've tried:

_foo: function () {
    function fooEvent() {
        this._bar();
        dojo.disconnect(updateHandle);
    }
    var updateHandle = dojo.connect(map, "onUpdateEnd", fooEvent());
}

_bar is the method I want to run on the end of the extent change. However, this in the event handler means something else, not the class containing the function. I also tried the classname I declared in the declare statement, but with no luck.

_foo() and _bar() are in the same class (let's call it "foobar/baz"). However, inside of the fooEvent() is not its subclass as I hoped - when I try to use this.inherited within it, it's undefined. Another way I try is to add event argument to the handler, but it's undefined as well. So unless there is some better way, I need to understand how to get the object of "foobar/baz" class.

Another way I tried was to use lang.hitch once more, in one of the following ways:

//through the cluster event
var updateHandle = dojo.connect(map, "onUpdateEnd", lang.hitch(this, clusterEvent));

//or directly calling _bar()
var updateHandle = dojo.connect(map, "onUpdateEnd", { langh:lang.hitch(this, this._bar), disc:dojo.disconnect(updateHandle)});

//or through on, leaving a rouge event listener
dojo.on(map, "onUpdateEnd", lang.hitch(this, this._bar));

None of them returns any clear error and though the _bar() method seemed to work for some time, it doesn't work now - this is true for all three of the previous. I don't understand what these listeners do.

回答1:

I solved this issue by flattening the event listeners. First, I made a flag _reloadFlag, initialized in the constructor as false and then changed to true whenever I want to call _bar, like in _foo. _bar now starts with a test of _reloadFlag either setting it to false or returning nothing. The event listeners now look like this:

this.events.push(on(this.map, "extent-change", lang.hitch(this, this._foo)));
this.events.push(on(this.map, "update-end", lang.hitch(this, this._bar)));

来源：https://stackoverflow.com/questions/35751571/how-to-link-extent-change-and-update-end-events-in-dojo