iPhone Development 101

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iPhone Development 101: Objective-C:
Objective-C: Custom URL Schemes

The scheme name (or protocol) of a URL is the first part of a URL - e.g. schemename://. For web pages, the scheme is usually http (or https). The iPhone supports these URL schemes:

http, https, ftp Web links* (Safari)
mailto E-mail links (launches the Mail app)
tel Telephone Numbers (launches the phone app)
sms Text Messages (launches the SMS app)

* Web links that point to http://maps.google.com are redirected to the Maps app.
* Web links that point to http://www.youtube.com are redirected to the YouTube app.
* iTunes store links (http://phobos.apple.com/etc..) are sent to the iTunes (or App store) app.

iPhone apps can also specify their own custom URL scheme (for example, myapp://doStuff). When might you want to use a custom URL scheme for your app?

Implementing a Custom URL Scheme

Defining your app's custom URL scheme is all done in the Info.plist file. Click on the last line in the file and then click the "+" sign off to the right to add a new line. Select URL Types for the new item. Once that's added, click the grey arrow next to "URL Types" to show "Item 0". Set your URL identifier to a unique string - something like com.yourcompany.yourappname.

After you've set the URL identifier, select that line and click the "+" sign again, and add a new item for URL Schemes. Then click the grey arrow next to "URL Schemes" to reveal "Item 0". Set the value for Item 0 to be your URL scheme name.

Handling Custom URL Calls

In order for your app to respond when it receives a custom URL call, you must implement the application:handleOpenURL method in the application delegate class:

- (BOOL)application:(UIApplication *)application handleOpenURL:(NSURL *)url {
    // handler code here
}

Parsing the Custom URL

There are several parts to a URL:

scheme://host/path?query

The parts to the URL can be retrieved through the NSURL object that is passed into the application:handleOpenURL method. If you have a fairly simple URL naming scheme and want to allow access to specific pages/keys, you can just use the host name:

Custom URL Value of [url host]:
myapp://page1 page1
myapp://page2 page2
myapp://otherPage otherPage

To pass data into your app, you'll want to use the query string. Here's a simple method for parsing the query string from the url:

- (NSDictionary *)parseQueryString:(NSString *)query {
    NSMutableDictionary *dict = [[[NSMutableDictionary alloc] initWithCapacity:6] autorelease];
    NSArray *pairs = [query componentsSeparatedByString:@"&"];
    
    for (NSString *pair in pairs) {
        NSArray *elements = [pair componentsSeparatedByString:@"="];
        NSString *key = [[elements objectAtIndex:0] stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
        NSString *val = [[elements objectAtIndex:1] stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
        
        [dict setObject:val forKey:key];
    }
    return dict;
}

Testing The Custom URL

You can easily test your URL scheme in the simulator. Just add a test button to one of your views, and implement the IBAction method for it as follows:

- (IBAction)getTest:(id)sender {
    [[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"myappscheme://test_page/one?token=12345&domain=foo.com"]];
}

Then in your app delegate, implement the application:handleOpenURL method:

- (BOOL)application:(UIApplication *)application handleOpenURL:(NSURL *)url {
    NSLog(@"url recieved: %@", url);
    NSLog(@"query string: %@", [url query]);
    NSLog(@"host: %@", [url host]);
    NSLog(@"url path: %@", [url path]);
    NSDictionary *dict = [self parseQueryString:[url query]];
    NSLog(@"query dict: %@", dict);
    return YES;
}

(You'll also need the parseQueryString method from above.)

Additional References


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