For the most part, NSScanner has everything we need to parse data types (int, float, string etc) from a string.

The following is a simple method that will convert a hexadecimal color (e.g. #FFCC88) into an equivalent UIColor object.

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- (UIColor *) colorForHex:(NSString *)hexColor {
	hexColor = [[hexColor stringByTrimmingCharactersInSet:
				 [NSCharacterSet whitespaceAndNewlineCharacterSet]
				] uppercaseString];  
 
    // String should be 6 or 7 characters if it includes '#'  
    if ([hexColor length] < 6) 
		return [UIColor blackColor];  
 
    // strip # if it appears  
    if ([hexColor hasPrefix:@"#"]) 
		hexColor = [cString substringFromIndex:1];  
 
    // if the value isn't 6 characters at this point return 
    // the color black	
    if ([hexColor length] != 6) 
		return [UIColor blackColor];  
 
    // Separate into r, g, b substrings  
    NSRange range;  
    range.location = 0;  
    range.length = 2; 
 
    NSString *rString = [hexColor substringWithRange:range];  
 
    range.location = 2;  
    NSString *gString = [hexColor substringWithRange:range];  
 
    range.location = 4;  
    NSString *bString = [hexColor substringWithRange:range];  
 
    // Scan values  
    unsigned int r, g, b;  
    [[NSScanner scannerWithString:rString] scanHexInt:&r];  
    [[NSScanner scannerWithString:gString] scanHexInt:&g];  
    [[NSScanner scannerWithString:bString] scanHexInt:&b];  
 
    return [UIColor colorWithRed:((float) r / 255.0f)  
                           green:((float) g / 255.0f)  
                            blue:((float) b / 255.0f)  
                           alpha:1.0f];  
 
}

Notice that we had to first separate our the hex values for the red, green, and blue components first as substrings and then apply the NSScanner to those substrings.

Before you get started, you need to figure out how you want you application to respond to the URL. The simplest way to use custom schemes is to just “wake up”; but it is also possible to pass information to the application via the URL, and in so doing, enable the application to do different things when woken up.

Registering Custom URL Schemes

Regardless of what you want to do once your application is started, the first step is to register a custom URL scheme with the iPhone. This is done via the info.plist file located in your application’s project folder (NOTE: this is the same file you would change to define a custom icon).

By default, when opened, XCode will edit the file in a graphical UI. It is possible to edit the info.plist file directly in Text mode which may be easier for some people.

Step 1. Right-Click and “Add Row”

Step 2. Select “URL types” as the Key

Step 3. Expand “Item 1″ and provide a value for the URL identifier. This can be any value, but the convention is to use a “reverse domain name” (ex “com.myapp”).

Step 4. Add another row, this time to “Item 1″.

Step 5. Select “URL Schemes” as the Key.

Step 6. Enter the characters that will become your URL scheme (e.g. “myapp://” would be “myapp”). It is possible for more than one scheme to be registered by adding to this section though that would be strange thing to do.

NOTE: If you open the info.plist file in a text editor you will see the following has been added to the file …

CFBundleURLTypes
 
    CFBundleURLSchemes
 
      myapp
 
    CFBundleURLName
    com.yourcompany.myapp

Optionally Handle the URL

Now that the URL has been registered. Anyone can start the application by opening a URL using your scheme.

Here are a few examples …

myapp://
 
myapp://some/path/here
 
myapp://?foo=1&bar=2
 
myapp://some/path/here?foo=1&bar=2

The iPhone SDK, when launching the application in response to any of the URLs above, will send a message to the UIApplicationDelegate.

If you want to provide a custom handler, simply provide an implementation for the message in your delegate. For example:

- (BOOL)application:(UIApplication *)application handleOpenURL:(NSURL *)url 
{
  // Do something with the url here
}

A common technique is to parse the URL passed in and pull from it the parameters that will be used by various views in the application and store them in the User Preference. Below is an example where we store the URL as a value parameter “url” in just such a manner …

- (BOOL)application:(UIApplication *)application handleOpenURL:(NSURL *)url
{
    if (!url) {  return NO; }
 
    NSString *URLString = [url absoluteString];
    [[NSUserDefaults standardUserDefaults] setObject:URLString forKey:@"url"];
    [[NSUserDefaults standardUserDefaults] synchronize];
    return YES;
}

Now you have everything you need to enable others to wake-up your application and even pass it information! Enjoy!

• Launch YouTube
• “Deep Link” to content in iTunes

YouTube Links

The YouTube URL scheme is used to launch the YouTube application and play the specified video. If your application links to YouTube content, you can use this scheme to play videos from your application.

NOTE:Unlike some schemes, YouTube URLs do not start with a “youtube” scheme identifier. Instead, they are specified as regular http links but are targeted at the YouTube server. The following examples show the basic strings you would use in Safari and an application to show a YouTube Video. In each example, you would need to replace the VIDEO_IDENTIFIER value with identifier of the video you wanted to display:

http://www.youtube.com/watch?v=VIDEO_IDENTIFIER

http://www.youtube.com/v/VIDEO_IDENTIFIER

iTunes Links

The iTunes URL scheme is used to link to content on the iTunes Music Store. The iTunes URL format is complicated to construct, so you create it using an online tool called iTunes Link Maker. The tool allows you to select a country destination and media type, and then search by song, album, or artist. After you select the item you want to link to, it generates the corresponding URL.

NOTE: For more information about the iTunes Link Maker applications take a look at this FAQ from Apple.

~/.subversion/config

NOTE: If the “.subversion” directory doesn’t exist yet then run this command which fails but will create the necessary files to get you started:

svn status

Step 2. Enable “global-ignores” and add new things to ignore

Find the line that contains the text “global-ignores” and append the following text:

build *~.nib *.so *.pbxuser *.mode* *.perspective*

Step 3. Enable “auto-properties”

Located and uncomment (e.g. remove the leading “#” character) the line that looks like this:

# enable-auto-props = yes

Step 4. Add additional properties

Then go to the end of the file, in the [auto-props] section, and append these lines:

*.mode* = svn:mime-type=text/X-xcode
*.pbxuser = svn:mime-type=text/X-xcode
*.perspective* = svn:mime-type=text/X-xcode
*.pbxproj = svn:mime-type=text/X-xcode

Take for example the following example …

Creating the mask above is really simple using CoreGraphics on the iPhone. The following is a function that takes two images and uses one to mask the other.

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- (UIImage*) maskImage:(UIImage *)image withMask:(UIImage *)maskImage {
 
	CGImageRef maskRef = maskImage.CGImage; 
 
	CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
		CGImageGetHeight(maskRef),
		CGImageGetBitsPerComponent(maskRef),
		CGImageGetBitsPerPixel(maskRef),
		CGImageGetBytesPerRow(maskRef),
		CGImageGetDataProvider(maskRef), NULL, false);
 
	CGImageRef masked = CGImageCreateWithMask([image CGImage], mask);
	return [UIImage imageWithCGImage:masked];
 
}

Yep … its just that simple!

NOTE: The mask image cannot have ANY transparency. Instead, transparent areas must be white or some value between black and white. The more towards black a pixel is the less transparent it becomes.

There is no special info.plist entry you need to make; as you would for the application icon. All that you need is to add the image as a resource to your project and make sure that it is located at the top level of the application and be spelled exactly like “Default.png” (NOTE: the ‘D’ must be capitalized).

To avoid “freezing” your application, ensure that any logic that is changing your UI is performed by the Main thread. One approach to this would be to leverage the NSNotificationCenter but sometimes that is overkill. A much simpler approach is to use one of the following performSelectorOnMainThread methods on NSObject:

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performSelectorOnMainThread:withObject:waitUntilDone:
performSelectorOnMainThread:withObject:waitUntilDone:modes:

Nine-times-out-of-ten this is the magic that will “thaw” your application and get it humming along again!

To disable the timer, set the idleTimerDisabled property to YES, like so …

[[UIApplication sharedApplication] setIdleTimerDisabled:YES];

Here are just some of the messages that have made my life a little easier …

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UIFont *myFont = [UIFont boldSystemFontOfSize:15.0];
// Get the width of a string ...
CGSize size = [@"Some string here!" sizeWithFont:myFont];
 
// Get the width of a string when wrapping within a particular width
NSString *loremIpsum = @"Lorem Ipsum Delores S...";
CGSize size = [loremIpsum sizeWithFont:myFont
                              forWidth:150.0 
		                lineBreakMode:UILineBreakModeWordWrap];

It is also possible to use this same technique to launch other applications on the iPhone that are very useful.

Examples of some of the key applications that you can launch via URL are:

• Launch the Browser (see earlier post )
• Launch Google Maps
• Launch Apple Mail
• Dial a Phone Number
• Launch the SMS Application
• Launch the Browser
• Launch the AppStore

Launch Google Maps

The URL string for launching Google Maps with a particular keyword follows this structure:

http://maps.google.com/maps?q=${QUERY_STRING}

The only trick to this is to ensure that the value for the ${QUERY_STRING} is properly URL encoded. Here is a quick example of how you would launch Google Maps for a specific address:

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// Create your query ...
NSString* searchQuery = @"1 Infinite Loop, Cupertino, CA 95014";
 
// Be careful to always URL encode things like spaces and other symbols that aren't URL friendly
searchQuery =  [addressText stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding];
 
// Now create the URL string ...
NSString* urlString = [NSString stringWithFormat:@"http://maps.google.com/maps?q=%@", searchQuery];
 
// An the final magic ... openURL!
[[UIApplication sharedApplication] openURL:[NSURL URLWithString:urlText]];

Launch Apple Mail

Also very useful, is the ability to enable a user to quickly send an email by launching the email client in compose mode and the address already filled out. The format of this URI should be familiar to anyone that has done any work with HTML and looks like this:

mailto://${EMAIL_ADDRESS}

For example, here we are opening the email application and filling the “to:” address with info@iphonedevelopertips.com :

[[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"mailto://info@iphonedevelopertips.com"]];

Dial a Phone Number (iPhone Only)

You can use openURL: to dial a phone number. One advantage this has over other URLs that launch applications, is that the dialer will return control back to the application when the user hits the “End Call” button.

Anyone familiar with J2ME or WML will find this URL scheme familiar:

tel://${PHONE_NUMBER}

Here is an example of how we would dial the number (800) 867-5309:

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[[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"tel://8004664411"]];

NOTE When providing an international number you will need to include the country code.

Launch the SMS Application

Also not supported by the iPod Touch, is the ability to quickly setup the SMS client so that your users can quickly send a text message. It is also possible to provide the body of the text message.

The format looks like this:

sms:${PHONENUMBER_OR_SHORTCODE}

NOTE: Unlike other URLs, an SMS url doesn’t use the “//” syntax. If you add these it will assume it is part of the phone number which is not.

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[[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"sms:55555"]];

NOTE: According to the official SMS specification, you should be able to send a body as well as the phone number by including “?body=” parameter on the end of the URL … unfortunately Apple doesn’t seem to support this standard.

Launching the AppStore

Finally, it is worth noting that you can launch the AppStore and have the "buy" page of a specific application appear. To do this, there is no special URL scheme. All you need to do is open up iTunes to the application you want to launch; right-click on the application icon at the top left of the page; and select Copy iTunes Store URL .

The URL will look something like this:

http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=291586600&mt=8

Launching the AppStore URL is exactly the same as you would launch the browser. Using the link above, here is an example of how we would launch the AppStore:

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NSURL *appStoreUrl = [NSURL URLWithString:@"http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=291586600&mt=8"];
[[UIApplication sharedApplication] openURL:appStoreUrl];