Adding a CallBack Function - Why and How by example.
You might like to review the original example first: .: POST :.
CallBack
A callback function is one that is not invoked explicitly by the programmer; rather the responsibility for its invocation is delegated to another function that receives the callback function's reference and instructions as to when to run the callback function.
Ouch! ...one might say. But not really.
It is the basis (sort-of) for understanding events: when this happens, do whatever is in this function.
In this fade in/out example, we may want to fade an image in and then do something else like start several place effects for other movie components. Or fade one image out and immediately fade another image in.
Not to get carried away, lets start simple and say after the fade-in/out let's simply pop-up an alert box.
So first we define a CallBack function, say cbFunc, to generate a simple JavaScript alert to say, "Done..."
In SWiSH, I define functions in the onLoad code sections like:
var cbFunc = function( name, type ) {
javascript( "alert('Done: "+name+" faded"+type+"');" );
};
Now, in our fader code, where would we want to invoke this pop-up?
Well certainly, when the fade-in/out has just completed. And in our code that is inside the setInterval loop, just after we stop the interval loop itself.
So, two changes to the prototype code:
1) add a parameter to pass the CallBack function reference:
MovieClip.prototype.rgbFade=function(type,func){
2) the code to call this function, if it was provided:
clearInterval(self.rgbIntervalID);
if(func) func(self._name, self.type);
delete self.rgbIntervalID;
And on our buttons:
Image.rgbFade( "In", cbFunc );
Image.rgbFade( "Out", cbFunc );
Note that if we do not supply the CallBack function:
Image.rgbFade( "In" );
...it works as before, no problem.
Example: .: LINK :.
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