The syntax for working with events looks like the code below.
+The syntax for working with events looks like the code below.
-Assuming for a moment that we want to observe when a link was clicked, +
Assuming for a moment that we want to observe when a link was clicked, we could do the following:
-If we wanted to get the element that fired the event, we'd do this:
+If we wanted to get the element that fired the event, we'd do this:
-If we wanted to observe keystrokes for the entire document, we could do the following:
+If we wanted to observe keystrokes for the entire document, we could do the following:
-And lets say we wanted to keep track of what has been typed :
+And lets say we wanted to keep track of what has been typed :
-Prototype defines properties inside the event object for some +
Prototype defines properties inside the event object for some of the more common keys, so feel free to dig around in Prototype to see which ones those are.
-A final note on keypress events; If you'd like to detect a +
A final note on keypress events; If you'd like to detect a left click you can use Event.isLeftClick(event).
Drag and drop, dynamic element resizing, games, and +
Drag and drop, dynamic element resizing, games, and much more all require the ability to track the X and Y location of the mouse. Prototype makes this fairly simple. The code below tracks the X and Y position of the mouse and spits out those values into an input box named mouse.
-If we wanted to observe the mouse location when it was +
If we wanted to observe the mouse location when it was hovering over a certain element, we'd just change the document argument to the id or element that was relevant.
Event.stop(event) will stop the propagation of an event .
+Event.stop(event) will stop the propagation of an event .
Everything has been fairly straight forward so far, but things +
Everything has been fairly straight forward so far, but things start getting a little trickier when you need to work with events in and object-oriented environment. You have to deal with binding and funky looking syntax that might take a moment to get your head around.
-Lets look at some code so you can get a better understanding of what I'm talking about.
-Lets look at some code so you can get a better understanding of what I'm talking about.
+Whoa! What's going on here? Well, we've defined our a +
Whoa! What's going on here? Well, we've defined our a custom class EventDispenser. We're going to be using this class to setup events for our document. Most of this code is a rewrite of the code we looked at earlier except this time, we are working from inside an object.
-Looking at the initialize method, we can really see how +
Looking at the initialize method, we can really see how things are different now. Take a look at the code below:
-We've got iterators, binding and all sorts of stuff going on. +
We've got iterators, binding and all sorts of stuff going on. Lets break down what this chunk of code is doing.
-First we are hunting for a collection of elements based on +
First we are hunting for a collection of elements based on it's CSS selector. This uses the Prototype selector function $$(). After we've found the list items we are dealing with we send those into an each iteration where we will add our observers.
-Now looking at the code above, you'll notice the bindEvent function. +
Now looking at the code above, you'll notice the bindEvent function. This takes the method before it showTagName and treats it as the method that will be triggered when, in this case, someone clicks one of our list items.
-You'll also notice we pass this as an argument to the bindEvent function. +
You'll also notice we pass this as an argument to the bindEvent function. This simply allows us to reference the object in context EventDispenser inside our function showTagName(event). If the showTagName function requires additional parameters, you can attach them to the later parameters of bindEvent. For example
-Moving on, you'll see bind(this) attached to our iterator function. +
Moving on, you'll see bind(this) attached to our iterator function. This really has nothing to do with events, it is only here to allow me to use this inside the iterator. If we did not use bind(this), I could not reference the method showTagName inside the iterator.
-Ok, so we'll move on to looking at our methods that actually get +
Ok, so we'll move on to looking at our methods that actually get called when an event occurs. Since we've been dealing with showTagName, lets look at it.
-As you can see, this function accepts one argument--the event. +
As you can see, this function accepts one argument--the event. In order for us to get the element which fired the event we need to pass that argument to Event.element. Now we can manipulate it at will.
-This covers the most confusing parts of our code. The text above is also +
This covers the most confusing parts of our code. The text above is also relevant to the remaining parts of our code. If there is anything about this you don't understand, feel free to ask questions in the forum.
This one threw me for a loop the first time I tried to use it. +
This one threw me for a loop the first time I tried to use it. I tried something similar to what I did in the Event.observe call with the exception of using stopObserving, but nothing seemed to change. In other words, the code below does NOT work.
-What's the deal here? The reason this does not work is because there +
What's the deal here? The reason this does not work is because there is no pointer to the observer. This means that when we passed this.showTagName in the Event.observe method before hand, we passed it as an anonymous function. We can't reference an anonymous function because it simply does not have a pointer.
-So how do we get the job done? All we need to do is give the +
So how do we get the job done? All we need to do is give the observing function a pointer, or the jargon free version: Set a variable that points to this.showTagName. Ok, lets change our code a bit.
-Now we can remove the event listeners from our list like this:
-Now we can remove the event listeners from our list like this:
+