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jQuery wrapper for iScroll

Matteo Spinelli did a terrific job writing a Javascript library that allows scrolling the content of a DIV element on iPhone and Android web browsers. The library is well documented in his site http://cubiq.org/iscroll. I don’t think that it is a must-have but I find very comfortable to implement functionality in a consistent way. Since I am a big jQuery fan I decided to wrap Matteo’s library in a very simple jQuery plugin.

?View Code JAVASCRIPT
(function($){
    $.fn.iscroll = function(options){
		if(this.data('iScrollReady') == null){
			var that = this;
            var options =  $.extend({}, options);
				options.onScrollEnd = function(){
					that.triggerHandler('onScrollEnd', [this]);
				};
			arguments.callee.object  = new iScroll(this.get(0), options);
			// NOTE: for some reason in a complex page the plugin does not register
			// the size of the element. This will fix that in the meantime.
			setTimeout(function(scroller){
				scroller.refresh();
			}, 1000, arguments.callee.object);
			this.data('iScrollReady', true);
		}else{
			arguments.callee.object.refresh();
		}
		return arguments.callee.object;
	};
})(jQuery);

Basically you can use jQuery to select the content that you want to scroll and call ‘.iscroll()’ to add the behavior. If you need to overwrite the default parameters you pass an object with values that you wish to change. Here is an example of how to implement this:

?View Code JAVASCRIPT
$(function(){
	var elem = $('#content');
		elem.iscroll();
		elem.bind('onScrollEnd', function(e, iscroll){
			alert($(this).attr('id') +' - '+ iscroll);
		});
});

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When you call .iscroll() the library will find the parent element and make the content scrollable. This method will also return an instance of the iScroll class. If the method is called again it will refresh the content. This is convenient in case you modify the content dynamically (iScroll allows to detech DOM changes automatically).

The library dispatches an event name onScrollEnd when the scroll action is completed. In touch screen devices this library adds momentum. This means that the content will continue moving for a short time after the touchend event. By default the version 3.7 accepts a callback function that is trigger at the end of the animation. The wrapper overwrites the parameter and triggers a jQuery event instead. This approach will allow multiple callback functions.

Implementing doubletap on iPhones and iPads

When the iPhone first arrived, one of the coolest things that Apple did was to have Mobile Safari display a miniature view of an entire web site, allowing users to double tap and zoom into the portions of the site that they wanted to see. This clever solution to navigate large pages in a small screen came with a price.

If your site takes advantage of the double click functionality, when it is displayed on Mobile Safari you loose that capability, your clicks become touch events and the double click (double-tap) now belongs to the browser.

If you want to get the double click functionality back, the first thing you should know is that you can prevent the default browser behavior that takes your double click away. Once you have done that, you can easily re-implement the double click/touch behavior you lost. In your HTML page start with adding a meta tag to indicate the users are not allow to scale the page:

var isiOS = false;
var agent = navigator.userAgent.toLowerCase();
if(agent.indexOf('iphone') >= 0 || agent.indexOf('ipad') >= 0){
       isiOS = true;
}

Now you should be able to write code for iOS devices and for regular browsers

?View Code JAVASCRIPT
if(isiOS){
       // implement double-tap
}else{
       // implement double click
}

Adding double double tap is bit trickier. We need to measure the time between two consecutive touch events. If a user taps twice within 500 milliseconds (half a second), I can assume that the user meant double tap. Now keep in mind that two click/touch events are also fired. The trick is that we have to wait before we can fire a click/touch event and call our doubletap handler only if users click/tap very quickly.

Let’s go one step at the time. I will use jQuery to bind a touchend event to an element selector:

?View Code JAVASCRIPT
$(selector).bind('touchend', function(event){
       var now = new Date().getTime();
       var lastTouch = $(this).data('lastTouch') || now + 1 /** the first time this will make delta a negative number */;
       var delta = now - lastTouch;
       if(delta <500 && delta>0){
               // the second touchend event happened within half a second. Here is where we invoke the double tap code
       }else{
               // A click/touch action could be invoked here but wee need to wait half a second before doing so.
       }
       $(this).data('lastTouch', now);
}

What I have done so far, is to determine the difference between the last touch and the current touch events. The first time that this code runs, both the current touch time and the last touch time are the same, so the delta is zero. At the end of the function I want to make sure that I update the value of the last touch to be equal to the current touch.

Now that we know where to write the double tap code, let’s figure out how to add some logic to help us know when to invoke the double tap code:

?View Code JAVASCRIPT
var action;
$(selector).bind('touchend', function(event){
       var now = new Date().getTime();
       var lastTouch = $(this).data('lastTouch') || now + 1 /** the first time this will make delta a negative number */;
       var delta = now - lastTouch;
       clearTimeout(action);
       if(delta<500 && delta>0){
               // the second touchend event happened within half a second. Here is where we invoke the double tap code
       }else{
               $(this).data('lastTouch', now);
               action = setTimeout(function(e){
                       // If this runs you can invoke your 'click/touchend' code
                       clearTimeout(action);   // clear the timeout
               }, 500, [event]);
       }
       $(this).data('lastTouch', now);
}

To determine how long we have to wait before we can tell that the user only tapped once, I added a timeout call declared outside of the touchend event handler. Every time that the touchend event is fired, I clear the action timeout which prevents the click/touch from happening. If the value of delta is less than 500 milliseconds (half a second) we can definitely invoke the doubletap code, but if delta is higher that 500 milliseconds the timeout is defined again and our click/touch code will be invoked in half a second.

Let’s put everything together and write it as a jQuery extension:

?View Code JAVASCRIPT
/*!
 * jQuery Double Tap Plugin.
 *
 * Copyright (c) 2010 Raul Sanchez (http://www.sanraul.com)
 *
 * Dual licensed under the MIT and GPL licenses:
 * http://www.opensource.org/licenses/mit-license.php
 * http://www.gnu.org/licenses/gpl.html
 */
 
(function($){
	// Determine if we on iPhone or iPad
	var isiOS = false;
	var agent = navigator.userAgent.toLowerCase();
	if(agent.indexOf('iphone') >= 0 || agent.indexOf('ipad') >= 0){
	       isiOS = true;
	}
 
	$.fn.doubletap = function(onDoubleTapCallback, onTapCallback, delay){
		var eventName, action;
		delay = delay == null? 500 : delay;
		eventName = isiOS == true? 'touchend' : 'click';
 
		$(this).bind(eventName, function(event){
			var now = new Date().getTime();
			var lastTouch = $(this).data('lastTouch') || now + 1 /** the first time this will make delta a negative number */;
			var delta = now - lastTouch;
			clearTimeout(action);
			if(delta0){
				if(onDoubleTapCallback != null && typeof onDoubleTapCallback == 'function'){
					onDoubleTapCallback(event);
				}
			}else{
				$(this).data('lastTouch', now);
				action = setTimeout(function(evt){
					if(onTapCallback != null && typeof onTapCallback == 'function'){
						onTapCallback(evt);
					}
					clearTimeout(action);   // clear the timeout
				}, delay, [event]);
			}
			$(this).data('lastTouch', now);
		});
	};
})(jQuery);

Usage:

?View Code JAVASCRIPT
$(selector).doubletap(
    /** doubletap-dblclick callback */
    function(event){
        alert('double-tap');
    },
    /** touch-click callback (touch) */
    function(event){
        alert('single-tap');
    },
    /** doubletap-dblclick delay (default is 500 ms) */
    400
);

This plugin will work on Desktop Browser as well as Mobile Safari. Click HERE to download the source code and basic examples. You can also visit the DEMO page.

Check out JQLoader v.0.1.0

Managing multiple Javascript libraries sometimes can become a challenge. If you write a library and it requires to include other existing libraries, and those libraries also require additional files, it is obvious that assembling your project will require from you to build a mental map where you have track all the dependencies. Often times I noticed that Javascript projects tend to be monolithic. Entire AJAX applications are written in one single file or directly in the HTML page, compromising the portability and scalability of a project. It is, in my opinion, a natural response to a problem that developers may not want to deal with.

jql-logoAs an exercise I decided to write a jQuery plugin to help managing Javascript libraries and their dependencies. JQLoader It is a very light wight plugin with a small set of API that are specifically created to help you organize your projects and simplify the way you assemble your code. If you have face issues loading multiple Javascript files, JQLoader could be a great allied to help you manage files and their dependencies. In a nutshell, you can divide your application into multiple files and JQLoader will stitch them for you, allowing combining the files that your application really needs.

Click HERE to check out the JQLoader Plugin page.

Developing Javascript Games for iPhone (part 1)

This is the my first serious attempt to do an iPhone application. Across the board, most of the smart cellphones support some kind of advance web browser that renders Javascript and HTML 5. Many people have already identified this as the common denominator. Webkit, an open source web browser engine is already part of iPhone and Android. It makes a lot of sense to build mobile applications in Javascript, HTML, and CSS and deploy them across multiple devices. Furthermore, frameworks such as PhoneGap and Titanium Appcelerator let you build Ajax applications and publish them as native apps on iPhone, Android and Blackberry.


What a great promise, right?. Mostly true, but there are a couple of things to keep in mind if we want to take advantage of the web browser capability and turn that into a game. I started this little exercise by choose a very simple game that I could write in Javascript in a few hours. The 15 Tile Puzzle game concept took about two hours to prototype.  Adding levels, creating some primitive graphics, debugging and testing, turned this little game into my weekend project.

Writing the game was pretty much as expected. Running the game in the iPhone was a bit disappointing. Although Webkit is an advance browser the game was not as responsive as the example that you see above. I used JQuery for some DOM manipulation as well as for animating the tiles in the game. Unfortunately, all this beauty of building web applications and running them on the iPhone comes with a price:

  • Rendering data is very easy but animating HTML element might be a little bit challenging, at least using JQuery ‘animate’.
  • Click, forget about it. The new devices introduced several new events that take priority over the well known ‘onclick’ event. Apple describe these new events and the sequence of executions in the Safari Web Content Guide.
  • When I used the ‘click’ event, there was a good ~0.5 second delay between the moment when I tap on the the screen and the moment when I saw my application responding. Some people recommend to use the JTouch plug-in, but I found a lot easier using JQuery to bind the new touch events ( $('#elem').bind('touchstart', {foo:123}, function(e){ ... 'e' is the new multitouch event ... }) ).
  • I missed Firebug when testing in the iPhone. Appcelerator has some debugging capability but probably I should look into the starndar iPhone development tools to get something better that ‘log()’.

On the bright side it is still exciting. With very little effort I was able to put together this little game and with the help of any of the framework that I mentioned earlier I will be able to turn my Tile Game into a real iPhone application.

For now if anyone wants to play it on the iPhone you can open Safari and go to http://www.sanraul.com/lab/tilegame/index.php.

I will write the part 2 of this post if I get the Tile Game to the AppStore.
Cheers!