Building iPhone Apps with HTML, CSS, and JavaScript

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Chapter 2. Basic iPhone Styling	Home	Chapter 4. Animation

Chapter 3. Advanced iPhone Styling

If you know HTML, CSS, and JavaScript, you already have what you need to develop your own iPhone apps. With this book, you'll learn how to use these open source web technologies to design and build apps for both the iPhone and iPod Touch. Buy the print book or ebook or purchase the iPhone App.

In our quest to build an iPhone app without Objective-C, we’ve so far learned how to use CSS to style a collection of HTML pages to look like an iPhone app. In this chapter, we’ll lay the groundwork to make those same pages behave like an iPhone app. Specifically, we’ll discuss using Ajax to turn a full website into a single-page app, how to create a back button with history using JavaScript, and how to take advantage of the Web Clip icon and full screen mode features of the iPhone to launch your app without Mobile Safari intruding upon the user experience.

Adding a Touch of Ajax

The term Ajax has become such a buzzword that I’m not even sure I know what it means anymore. For the purposes of this book, I’m going to use Ajax to refer to the technique of using JavaScript to send requests to a web server without reloading the current page (e.g., to retrieve some HTML, submit a form, and so on). This approach makes for a very smooth user experience, but does require that you reinvent a lot of wheels.

For example, if you are loading external pages dynamically, the browser will not give any indication of progress or errors to the users. Furthermore, the back button will not work as expected unless you take pains to support it. In other words, you have to do a lot of work to make a sweet Ajax app. Even so, there are some very good reasons to go to the trouble. In particular, it opens the door to creating iPhone apps that can run full-screen (the section called “Full Screen Mode”) and even offline (Chapter 6, Going Offline).

Traffic Cop

For my next series of examples, I’m going to write a single page called iphone.html that will sit in front of all of the site’s other pages and will handle requests, sort of like a traffic cop. Here’s how it works. On first load, iphone.html will present the user with a nicely formatted version of the site navigation. I’ll then use jQuery to “hijack” the onclick actions of the nav links so that when the user clicks on one, the browser page will not navigate to the target link. Rather, jQuery will load a portion of the HTML from the remote page and deliver the data to the user by updating the current page. I’ll start with the most basic functional version of the code and improve it as we go along.

The HTML for the iphone.html wrapper page is extremely simple (see Example 3.1, “This simple HTML wrapper markup will sit in front of all the site’s other pages”). In the head section, I set the title and viewport options, and include links to a stylesheet (iphone.css) and two JavaScript files: jquery.js and a custom JavaScript file named iphone.js.

Note

For more information on where to get jquery.js and what to do with it, see the section called “Intro to JavaScript”.

The body just has two div containers: a header with the initial title in an h1 tag, and an empty div container, which will end up holding HTML snippets retrieved from other pages.

Example 3.1. This simple HTML wrapper markup will sit in front of all the site’s other pages

<html>
<head>
    <title>Jonathan Stark</title>
    <meta name="viewport" content="user-scalable=no, width=device-width" />
    <link rel="stylesheet" href="iphone.css" type="text/css" media="screen" />
    <script type="text/javascript" src="jquery.js"></script>
    <script type="text/javascript" src="iphone.js"></script>
</head>
<body>
    <div id="header"><h1>Jonathan Stark</h1></div>
    <div id="container"></div>
</body>
</html>

Moving on to the iphone.css file, you can see in Example 3.2, “The base CSS for the page is just a slightly reshuffled version of previous examples” that I’ve reshuffled some of the properties from previous examples (e.g., some of the #header h1 properties have been moved up to #header). Overall, though, everything should look familiar (if not, please review ).

Example 3.2. The base CSS for the page is just a slightly reshuffled version of previous examples

body {
    background-color: #ddd;
    color: #222;
    font-family: Helvetica;
    font-size: 14px;
    margin: 0;
    padding: 0;
}
#header {
    background-color: #ccc;
    background-image: -webkit-gradient(linear, left top, left bottom, from(#ccc), to(#999));
    border-color: #666;
    border-style: solid;
    border-width: 0 0 1px 0;
}
#header h1 {
    color: #222;
    font-size: 20px;
    font-weight: bold;
    margin: 0 auto;
    padding: 10px 0;
    text-align: center;
    text-shadow: 0px 1px 0px #fff;
}
ul {
    list-style: none;
    margin: 10px;
    padding: 0;
}
ul li a {
    background-color: #FFF;
    border: 1px solid #999;
    color: #222;
    display: block;
    font-size: 17px;
    font-weight: bold;
    margin-bottom: -1px;
    padding: 12px 10px;
    text-decoration: none;
}
ul li:first-child a {
    -webkit-border-top-left-radius: 8px;
    -webkit-border-top-right-radius: 8px;
}
ul li:last-child a {
    -webkit-border-bottom-left-radius: 8px;
    -webkit-border-bottom-right-radius: 8px;
}
ul li a:active,ul li a:hover {
    background-color:blue;
    color:white;
}
#content {
    padding: 10px;
    text-shadow: 0px 1px 0px #fff;
}
#content a {
    color: blue;
}

The JavaScript in iphone.js is where all the magic happens in this example. Please refer to Example 3.3, “This bit of JavaScript in iphone.js converts the links on the page to Ajax requests” as I go through it line by line.

Note

This JavaScript loads a document called index.html, and will not work without it. You should reuse the HTML file from Chapter 2, Basic iPhone Styling, being sure to save it as index.html in the same directory as the iphone.html you created earlier in this chapter. However, none of the links in it will work unless the targets of the links actually exist. You can create these files yourself or download the example code from the book’s website. Creating about.html, blog.html, and consulting-clinic.html will give you a few links to play with. To do so, just duplicate index.html a few times and change the filename of each copy to match the related link. For added effect, you can change the content of the h2 tag in each file to match the filename. For example, the h2 in blog.html would be <h2>Blog</h2>.

Example 3.3. This bit of JavaScript in iphone.js converts the links on the page to Ajax requests

$(document).ready(function(){ 
    loadPage();
});
function loadPage(url) {
   if (url == undefined) {
      $('#container').load('index.html #header ul', hijackLinks);
   } else {
      $('#container').load(url + ' #content', hijackLinks);
   }
}
function hijackLinks() {
    $('#container a').click(function(e){
        e.preventDefault();
        loadPage(e.target.href);
    });
}

	Here I’m using jQuery’s document ready function to have the browser run the `loadPage()` function when the DOM is complete.
	The `loadPage()` function accepts a single parameter called `url`, and then checks (on the next line) whether a value has been sent.
	If a value is not sent into the function, `url` will be undefined and this line will execute. This line and the following are examples of jQuery’s `load()` function. The `load()` function is excellent for adding quick and dirty Ajax functionality to a page. If this line were translated into English, it would read: “Get all of the `ul` elements from the `#header` element of `index.html` and insert them into the `#container` element of the current page. When you’re done, run the `hijackLinks()` function.” Note that `index.html` refers to the home page of the site. If your home page is named differently, you’d use that filename here instead.
	This line is executed if the `url` parameter has a value. It says, in effect: “Get the `#content` element from the `url` that was passed into the `loadPages()` function and insert it into the `#container` element of the current page. When you’re done, run the `hijackLinks()` function.”
	Once the `load()` function has completed, the `#container` element of the current page will contain the HTML snippet that was retrieved. Then, `load()` will run the `hijackLinks()` function.
	On this line, `hijackLinks()` finds all of the links that are in the new HTML, and binds a click handler to them using the lines of code that follow. Click handlers are automatically passed an event object, which I’m capturing as the function parameter `e`. The event object of a clicked link contains the URL of the remote page in `e.target.href`.
	Normally, a web browser will navigate to a new page when a link is clicked. This navigation response is called the “default behavior” of the link. Since we are handling clicks and loading pages manually, we need to prevent this default behavior. On this line, I’ve done so by calling the built-in `preventDefault()` method of the event object. If I had left that line out, the browser would have dutifully left the current page and navigated to the URL of the clicked link.
	When the user clicks, I pass the URL of the remote page to the `loadPage()` function and the cycle starts all over again.

Tip

One of my favorite things about JavaScript is that you can pass a function as a parameter to another function. Although this looks weird at first, it’s extremely powerful and allows you to make your code modular and reusable. If you’d like to learn more, you should check out JavaScript: The Good Parts by Douglas Crockford (O’Reilly). In fact, if you are working with JavaScript, you should check out everything by Douglas Crockford; you’ll be glad you did.

Click handlers do not run when the page first loads; they run when the user has read some stuff on the page and decides to click a link. Assigning click handlers is like setting booby traps; you do some initial setup work for something that may or may not be triggered later.

Tip

It’s worth taking a few minutes to read up on the properties of the event object that JavaScript creates in response to user actions in the browser. A good reference is located at http://www.w3schools.com/htmldom/dom_obj_event.asp.

Simple Bells and Whistles

With this tiny bit of HTML, CSS, and JavaScript, we have essentially turned an entire website into a single-page application. However, it still leaves quite a bit to be desired. Let’s slick things up a bit.

Since we are not allowing the browser to navigate from page to page, the user will not see any indication of progress while data is loading. We need to provide some feedback to let users know that something is, in fact, happening. Without this feedback, users will wonder if they actually clicked the link or missed it, and will often start clicking all over the place in frustration. This can lead to increased server load and application instability (i.e., crashing).

Note

If you are testing this web application on a local network, the network speeds will be so fast you won’t ever see the progress indicator. If you are using Mac OS X, you can slow all incoming web traffic by typing a couple of ipfw commands at the terminal. For example, these commands will slow all web traffic to 4 kilobytes per second:

sudo ipfw pipe 1 config bw 4KByte/s
sudo ipfw add 100 pipe 1 tcp from any to me 80

If you are using the Safari desktop browser to view the pages, you’ll need to use your Mac’s hostname or external IP address in the URL (for example, mymac.local rather than localhost). When you’re done testing, delete the rule with sudo ipfw delete 100 (you can delete all custom rules with ipfw flush).

Thanks to jQuery, providing this sort of feedback only takes two lines of code. We’ll just append a loading div to the body when loadPage() starts, and remove the loading div when hijackLinks() is done. Example 3.4, “Adding a simple progress indicator to the page” shows a modified version of Example 3.3, “This bit of JavaScript in iphone.js converts the links on the page to Ajax requests”. The lines you need to add to iphone.js are shown in bold.

Example 3.4. Adding a simple progress indicator to the page

$(document).ready(function(){
    loadPage();
});
function loadPage(url) {
    $('body').append('<div id="progress">Loading...</div>');
    if (url == undefined) {
        $('#container').load('index.html #header ul', hijackLinks);
    } else {
        $('#container').load(url + ' #content', hijackLinks);
    }
}
function hijackLinks() {
    $('#container a').click(function(e){
        e.preventDefault();
        loadPage(e.target.href);
    });
    $('#progress').remove();
}

See Example 3.5, “CSS added to iphone.css used to style the progress indicator” for the CSS that needs to be added to iphone.css to style the progress div. The result can be seen in Figure 3.1, “Without a progress indicator of some kind, your app will seem unresponsive and your users will get frustrated”.

Figure 3.1. Without a progress indicator of some kind, your app will seem unresponsive and your users will get frustrated

Example 3.5. CSS added to iphone.css used to style the progress indicator

#progress {
    -webkit-border-radius: 10px;
    background-color: rgba(0,0,0,.7);
    color: white;
    font-size: 18px;
    font-weight: bold;
    height: 80px;
    left: 60px;
    line-height: 80px;
    margin: 0 auto;
    position: absolute;
    text-align: center;
    top: 120px;
    width: 200px;
}

My site happens to have a single h2 at the beginning of each page that would make a nice page title (see Figure 3.2, “Before moving the page heading to the toolbar...”). You can see this in the HTML source shown in Chapter 2, Basic iPhone Styling. To be more iPhone-esque, I’m going to pull that title out of the content and put it in the header (see Figure 3.3, “...and after moving the page heading to the toolbar”). Again, jQuery to the rescue: you can just add three lines to the hijackLinks() function to make it happen. Example 3.6, “Using the h2 from the target page as the toolbar title” shows the hijackLinks function with these changes.

Figure 3.2. Before moving the page heading to the toolbar...

Figure 3.3. ...and after moving the page heading to the toolbar

Example 3.6. Using the h2 from the target page as the toolbar title

function hijackLinks() {
    $('#container a').click(function(e){
        e.preventDefault();
        loadPage(e.target.href);
    });
    var title = $('h2').html() || 'Hello!';
    $('h1').html(title);
    $('h2').remove();
    $('#progress').remove();
}

Note

Note that I added the title lines before the line that removes the progress indicator. I like to remove the progress indicator as the very last action because I think it makes the application feel more responsive.

The double pipe (||) in the first line of inserted code (shown in bold) is the JavaScript logical operator OR. Translated into English, that line would read: “Set the title variable to the HTML contents of the h2 element, or to the string ‘Hello!’ if there is no h2 element.” This is important because the first page load won’t contain an h2, as we are just grabbing the nav uls.

Note

This point probably needs some clarification. When users first load the iphone.html URL, they are only going to see the overall site navigation elements, as opposed to any site content. They won’t see any site content until they tap a link on this initial navigation page.

A few pages on my site have titles that are longer than can fit in the header bar (Figure 3.4, “Text wrapping in the toolbar is not very iPhone-ish...”). I could just let the text break onto more than one line, but that would not be very iPhone-ish. Rather, I’ve updated the #header h1 styles such that long text will be truncated with a trailing ellipsis (see Figure 3.5, “...but we can beautify it with a CSS ellipsis” and Example 3.7, “Adding an ellipsis to text that is too long for its container”). This might be my favorite little-known CSS trick.

Figure 3.4. Text wrapping in the toolbar is not very iPhone-ish...

Figure 3.5. ...but we can beautify it with a CSS ellipsis

Example 3.7. Adding an ellipsis to text that is too long for its container

#header h1 {
    color: #222;
    font-size: 20px;
    font-weight: bold;
    margin: 0 auto;
    padding: 10px 0;
    text-align: center;
    text-shadow: 0px 1px 0px #fff;
    max-width: 160px;
    overflow: hidden;
    white-space: nowrap;
    text-overflow: ellipsis;
}

Here’s the rundown: max-width: 160px instructs the browser not to allow the h1 element to grow wider than 160px. Then, overflow: hidden instructs the browser to chop off any content that extends outside of the element borders. Next, white-space: nowrap prevents the browser from breaking the line into two. Without this line, the h1 would just get taller to accommodate the text at the defined width. Finally, text-overflow: ellipsis appends three dots to the end of any chopped-off text to indicate to users that they are not seeing the entire string.

Let’s say you have an About page that is longer than the viewable area on the iPhone. The user visits the page, scrolls down to the bottom, and clicks on a link to your Contact page. If you have more than a screenful of text on your Contact page, the new data will appear with the window still scrolled all the way to the bottom.

Technically, this makes sense because we are not actually leaving the current (scrolled) page, but it’s certainly confusing for the user. To rectify the situation, I have added a scrollTo() command to the loadPage() function (see Example 3.8, “It’s a good idea to scroll back to the top when a user navigates to a new page”).

Now whenever a user clicks a link, the page will first jump to the top. This has the added benefit of ensuring that the loading graphic is visible if the user clicks a link at the bottom of a long page.

Example 3.8. It’s a good idea to scroll back to the top when a user navigates to a new page

function loadPage(url) {
    $('body').append('<div id="progress">Loading...</div>');
    scrollTo(0,0);
    if (url == undefined) {
        $('#container').load('index.html #header ul', hijackLinks);
    } else {
        $('#container').load(url + ' #content', hijackLinks);
    }
}

Like most sites, mine has links to external pages (i.e., pages hosted on other domains). I don’t want to hijack these external links because it wouldn’t make sense to inject their HTML into my iPhone-specific layout. In Example 3.9, “You can allow external pages to load normally by checking the domain name of the URL”, I have added a conditional that checks the URL for the existence of my domain name. If it’s found, the link is hijacked and the content is loaded into the current page; that is, Ajax is in effect. If not, the browser will navigate to the URL normally.

Caution

You must change jonathanstark.com to the appropriate domain or hostname for your website, or the links to pages on your website will no longer be hijacked.

Example 3.9. You can allow external pages to load normally by checking the domain name of the URL

function hijackLinks() {
    $('#container a').click(function(e){
        var url = e.target.href;
        if (url.match(/jonathanstark.com/)) {
            e.preventDefault();
            loadPage(url);
        }
    });
    var title = $('h2').html() || 'Hello!';
    $('h1').html(title);
    $('h2').remove();
    $('#progress').remove();
}

Tip

The url.match function uses a language, regular expressions, that is often embedded within other programming languages such as JavaScript, PHP, and Perl. Although this regular expression is simple, more complex expressions can be a bit intimidating, but are well worth becoming familiar with. My favorite regex page is located at http://www.regular-expressions.info/javascriptexample.html.

Roll Your Own Back Button

The elephant in the room at this point is that the user has no way to navigate back to previous pages (remember that we’ve hijacked all the links, so the Safari page history won’t work). Let’s address that by adding a back button to the top-left corner of the screen. First, I’ll update the JavaScript, and then I’ll do the CSS.

Adding a standard iPhone-ized back button to the app means keeping track of the user’s click history. To do this, we’ll have to A) store the URL of the previous page so we know where to go back to, and B) store the title of the previous page so we know what label to put on the back button.

Adding this feature touches on most of the JavaScript we’ve written so far in this chapter, so I’ll go over the entire new version of iphone.js line by line (see Example 3.10, “Expanding the existing JavaScript example to include support for a back button”). The result will look like Figure 3.6, “It wouldn’t be an iPhone app without a glossy, left-arrow back button”.

Figure 3.6. It wouldn’t be an iPhone app without a glossy, left-arrow back button

Example 3.10. Expanding the existing JavaScript example to include support for a back button

 var hist = [];
 var startUrl = 'index.html';
 $(document).ready(function(){
     loadPage(startUrl);
 });
 function loadPage(url) {
    $('body').append('<div id="progress">Loading...</div>');
    scrollTo(0,0);
    if (url == startUrl) {
        var element = ' #header ul';
    } else {
        var element = ' #content';
    }
    $('#container').load(url + element, function(){
        var title = $('h2').html() || 'Hello!';
        $('h1').html(title);
        $('h2').remove();
        $('.leftButton').remove();
        hist.unshift({'url':url, 'title':title});
        if (hist.length > 1) {
            $('#header').append('<div class="leftButton">'+hist[1].title+'</div>');
            $('#header .leftButton').click(function(){
                var thisPage = hist.shift();
                var previousPage = hist.shift();
                loadPage(previousPage.url);
            });
        }
        $('#container a').click(function(e){
            var url = e.target.href;
            if (url.match(/jonathanstark.com/)) {
                e.preventDefault();
                loadPage(url);
            }
        });
        $('#progress').remove();
    });
}

	On this line, I’m initializing a variable named `hist` as an empty array. Since I’ve defined it outside of any functions, it exists in the global scope and will be available everywhere in the page. Note that I didn’t use the full word `history` as my variable name because that is a predefined object property in JavaScript and should be avoided in your own code.
	Here I’m defining the relative URL of the remote page to load when the user first visits `iphone.html`. You might recall from earlier examples that I just checked for `url == undefined` to handle the first page load, but in this example we are going to use the start page in a few places. Therefore, it makes sense to define it globally.
	This line and the next make up the document ready function definition. Note that unlike previous examples, I’m passing the start page to the `loadPage()` function.
	On to the `loadPage()` function. This line and the next are verbatim from previous examples.
	This `if...else` statement determines which elements to load from the remote page. For example, if we want the start page, we grab the `ul`s from the header; otherwise, we grab the content `div`.
	On this line, the URL parameter and the appropriate source element are concatenated as the first parameter passed to the load function. As for the second parameter, I’m passing an anonymous function (an unnamed function that is defined inline) directly. As we go through the anonymous function, you’ll notice a strong resemblance to the `hijackLinks()` function, which this anonymous function has replaced. For example, the following three lines are identical to previous examples.
	On this line, I’m removing the `.leftButton` object from the page. (This might seem weird because I haven’t yet added it to the page; we’ll be adding it a couple steps down.)
	Here I’m using the built-in `unshift` method of the JavaScript array to add an object to the beginning of the `hist` array. The object I’m adding has two properties, `url` and `title`, which are the two pieces of information we need to support the back button display and behavior.
	On this line, I’m using the built-in `length` method of the JavaScript array to find out how many objects are in the history array. If there is only one object in the history array, it means that the user is on the first page, and therefore we don’t need to display a back button. However, if there is more than one object in the `hist` array, we need to add a button to the header.
	Next, I’m adding that `.leftButton` I mentioned earlier. The text of the button will be the same as the title of the page before the current page, which is what I’m accessing with the `hist[1].title` code. JavaScript arrays are zero-based, so the first item in the array (the current page) has an index of 0. In other words, index 0 is the current page, index 1 is the previous page, index 2 is the page before that, and so on.
	In this block of code, I’m binding an anonymous function to the click handler of the back button. Remember, click handler code executes when the user clicks, not when the page loads. So, after the page loads and the user clicks to go back, the code inside this function will run.
	This line and the next use the built-in `shift` method of the array to remove the first two items from the `hist` array, and the last line in the function sends the URL of the previous page to the `loadPage()` function.
	The remaining lines were copied exactly from previous examples, so I won’t rehash them here.
	This is the URL matching code introduced earlier in this chapter. Remember to replace `jonathanstark.com` with part of your website’s domain or hostname, or none of the local links will be hijacked and loaded into the page.

Tip

Please visit http://www.hunlock.com/blogs/Mastering_Javascript_Arrays for a full listing of JavaScript array functions with descriptions and examples.

Now that we have our back button, all that remains is to purty it up with some CSS (see Example 3.11, “Add the following to iphone.css to beautify the back button with a border image”). I start off by styling the text with font-weight, text-align, line-height, color, and text-shadow. I continue by placing the div precisely where I want it on the page with position, top, and left. Then, I make sure that long text on the button label will truncate with an ellipsis using max-width, white-space, overflow, and text-overflow. Finally, I apply a graphic with border-width and -webkit-border-image. Unlike my earlier border image example, this image has a different width for the left and right borders, because the image is made asymmetrical by the arrowhead on the left side.

Note

Don’t forget that you’ll need an image for this button. You’ll need to save it as back_button.png in the images folder underneath the folder that holds your HTML file. See the section called “Adding Basic Behavior with jQuery” for tips on finding or creating your own button images.

Example 3.11. Add the following to iphone.css to beautify the back button with a border image

#header div.leftButton {
    font-weight: bold;
    text-align: center;
    line-height: 28px;
    color: white;
    text-shadow: rgba(0,0,0,0.6) 0px -1px 0px;
    position: absolute;
    top: 7px;
    left: 6px;
    max-width: 50px;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    border-width: 0 8px 0 14px;
    -webkit-border-image: url(images/back_button.png) 0 8 0 14;
}

By default, Mobile Safari briefly displays a translucent gray box over clickable objects that have been tapped (Figure 3.7, “By default, Mobile Safari displays a translucent gray box over clickable objects that have been tapped”). Since our back button is not rectangular, this effect looks a little lame, but removing it is easy and makes the app look much better. Mobile Safari supports a property called -webkit-tap-highlight-color that allows you to change the default to whatever color you like. I want to remove the highlight completely, which I’ve done here by setting the tap highlight to a fully transparent color (see Example 3.12, “Add the following to iphone.css to remove the default tap highlight from Mobile Safari”).

Figure 3.7. By default, Mobile Safari displays a translucent gray box over clickable objects that have been tapped

Example 3.12. Add the following to iphone.css to remove the default tap highlight from Mobile Safari

#header div.leftButton {
    font-weight: bold;
    text-align: center;
    line-height: 28px;
    color: white;
    text-shadow: rgba(0,0,0,0.6) 0px -1px 0px;
    position: absolute;
    top: 7px;
    left: 6px;
    max-width: 50px;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    border-width: 0 8px 0 14px;
    -webkit-border-image: url(images/back_button.png) 0 8 0 14;
    -webkit-tap-highlight-color: rgba(0,0,0,0);
}

In the case of the back button, there can be at least a second or two of delay before the content from the previous page appears. To avoid frustration, I want the button to look clicked the instant it’s tapped. In a desktop browser, this would be a simple process; you’d just add a declaration to your CSS using the :active pseudoclass to specify an alternate style for the object that was clicked. I don’t know whether it’s a bug or a feature, but this approach does not work on the iPhone; the :active style is ignored.

I toyed around with combinations of :active and :hover, which brought me some success with non-Ajax apps. However, with an Ajax app like the one we are using here, the :hover style is sticky (i.e., the button appears to remain “clicked” even after the finger is removed).

Fortunately, the fix is pretty simple. I use jQuery to add the class clicked to the button when the user taps it. I’ve opted to apply a darker version of the button image to the button in the example (see Figure 3.8, “It’s a subtle difference, but the clicked back button is a bit darker than the default state” and Example 3.13, “Add the following to iphone.css to make the back button look clicked the moment the user taps it”). You’ll need to make sure you have a button image called back_button_clicked.png in the images subfolder. See the section called “Adding Basic Behavior with jQuery” for tips on finding or creating your own button images.

Figure 3.8. It’s a subtle difference, but the clicked back button is a bit darker than the default state

Example 3.13. Add the following to iphone.css to make the back button look clicked the moment the user taps it

#header div.leftButton.clicked {
    -webkit-border-image: url(images/back_button_clicked.png) 0 8 0 14;
}

Note

Since I’m using an image for the clicked style, it would be smart to preload the image. Otherwise, the unclicked button graphic will disappear the first time it’s tapped while the clicked graphic downloads. I’ll cover image preloading in the next chapter.

With the CSS in place, I can now update the portion of iphone.js that assigns the click handler to the back button. First, I add a variable, e, to the anonymous function in order to capture the incoming click event. Then, I wrap the event target in a jQuery selector and call jQuery’s addClass() function to assign my clicked CSS class to the button:

$('#header .leftButton').click(function(e){
    $(e.target).addClass('clicked');
    var thisPage = hist.shift();
    var previousPage = hist.shift();
    loadPage(previousPage.url);
});

Note

A special note to any CSS gurus in the crowd: the CSS Sprite technique—popularized by A List Apart—is not an option in this case because it requires setting offsets for the image. Image offsets are not supported by the -webkit-border-image property.

Adding an Icon to the Home Screen

Hopefully users will want to add an icon for your web app (called a “Web Clip icon”) to their home screens. They do this by tapping the plus button at the bottom of the Safari window (Figure 3.9, “Adding a Web Clip icon to your home screen, Step 1: click the plus button at the bottom of the Safari window”), tapping Add to Home Screen (Figure 3.10, “Step 2: click the “Add to Home Screen” button in the dialog”), and clicking the Add button (Figure 3.11, “Step 3: click the “Add” button in the “Add to Home” panel”). By default, the iPhone will create this icon by thumbnailing the current page (including position and zoom) and applying rounded corners and a glossy effect (Figure 3.12, “Step 4: a 57 × 57 pixel image will show up on the home screen”).

Figure 3.9. Adding a Web Clip icon to your home screen, Step 1: click the plus button at the bottom of the Safari window

Figure 3.10. Step 2: click the “Add to Home Screen” button in the dialog

Figure 3.11. Step 3: click the “Add” button in the “Add to Home” panel

Figure 3.12. Step 4: a 57 × 57 pixel image will show up on the home screen

To customize the home screen image, the cool kids provide a custom Web Clip icon. The simplest way to do this is to specify a single icon for your entire site by uploading a file named apple-touch-icon.png to your web root. The file should be 57 pixels square, and without gloss or rounded corners because the iPhone will add these automatically. If you don’t want the iPhone to add effects to your Web Clip icon, change the name of the file to apple-touch-icon-precomposed.png.

In some cases, you may want to provide a Web Clip icon for a page that is different from the rest of your site. You can do this by adding one of the following lines to the head section of the “traffic cop” HTML document, iphone.html (replacing myCustomIcon.png with the absolute or relative path to the image):

<link rel="apple-touch-icon" href="myCustomIcon.png" />

<link rel="apple-touch-icon-precomposed" href="myCustomIcon.png" />

Note

If you are going to use precomposed images, make the corner radius 10 pixels or more; otherwise, the iPhone will round the corners to 10 pixels. In either case, using precomposed images does suppress the addition of the glossy effect.

Full Screen Mode

Feel like reclaiming a quarter of the available vertical space from Mobile Safari (104 pixels, to be precise)? Add the following line to the head section of the “traffic cop” HTML document, iphone.html, and your web app will display in full screen mode when launched from the Web Clip icon:

<meta name="apple-mobile-web-app-capable" content="yes" />

I would’ve told you about this feature earlier, but it’s only useful once you have hijacked all of your hyperlinks with Ajax. As soon as a user clicks on a nonhijacked link—one that actually navigates to a new page—Mobile Safari will launch and load the page normally. This behavior is perfect for the example we’ve been working with because external links (Amazon, Twitter, Facebook, etc.) will open in Safari.

Changing the Status Bar

Once you’ve added the apple-mobile-web-app-capable meta tag, you have the option to control the background color of the 20-pixel status bar at the top of the screen using the apple-mobile-web-app-status-bar-style meta tag. The normal gray Safari status bar is the default, or you can change it to black (see Figure 3.13, “Full screen mode gives you about 25% more screen real estate and allows you to customize the appearance of the status bar”). You can also set it to black-translucent, which makes it partially transparent and additionally removes it from the document flow. In other words, your content will be shifted up by 20 pixels and behind the status bar when the page first loads, so you might have to position your header a little lower to compensate:

<meta name="apple-mobile-web-app-status-bar-style" content="black" />

Note

Changes to the status bar style will only take effect when the app is launched in full screen mode.

Figure 3.13. Full screen mode gives you about 25% more screen real estate and allows you to customize the appearance of the status bar

Providing a Custom Startup Graphic

When an app is launched in full screen mode, the user is presented with a screenshot of the app while the first page is loading. I’m not a fan of this because it looks like the app is ready to be interacted with, when in reality tapping a link will do nothing. Furthermore, the screenshot is based on the last page from the user’s previous visit, scrolled to wherever he left off—not very attractive.

Fortunately, Mobile Safari allows us to define a startup graphic that will be displayed while the page is loading. To add a custom startup graphic, create a 320px × 460px PNG file and place it in the same directory with iphone.html. Next, add the following line to the head section of iphone.html (you’d replace myCustomStartupGraphic.png with the absolute or relative path to your image):

<link rel="apple-touch-startup-image" href="myCustomStartupGraphic.png" />

The next time we launch our app from the Web Clip icon, the default loading behavior will take place while the new custom graphic is downloaded. On the subsequent launch, the custom startup graphic will be displayed (Figure 3.14, “Providing a custom startup graphic for an app launched in full screen mode”).

Figure 3.14. Providing a custom startup graphic for an app launched in full screen mode

What You’ve Learned

In this chapter, you’ve learned how to convert a normal website into a full-screen Ajax application, complete with progress indicators, a native-looking back button, and a custom Web Clip icon. In the next chapter, you’ll learn how to make your app come alive by adding native user interface animations. That’s right; here comes the fun stuff!

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