Understanding UIApplication’s handleOpenURL ‘Return’

As a developer working on iOS applications, you’ve likely encountered scenarios where you need to handle custom URL schemes. One common challenge is understanding what happens when handleOpenURL returns and how it affects the application flow.

In this article, we’ll delve into the world of handleOpenURL, explore its return value, and discuss approaches for passing data between views in your iOS app.

Overview of UIApplication’s handleOpenURL

When an application is launched or resumed, the application(_:open:options:) method is called on the app delegate. This method is responsible for handling URLs that are associated with a custom scheme (e.g., myapp://). The method takes three parameters:

1. UIApplication *application: The current application object.
2. NSURL *url: The URL to be handled.
3. NSDictionary *options: An optional dictionary containing additional information about the URL.

In this article, we’ll focus on the url parameter and its contents.

The Role of HandleOpenURL

When you specify a custom scheme in your app’s Info.plist file, iOS recognizes it as a potential URL handler. When a user navigates to a URL with this scheme, the application(_:open:options:) method is called on the app delegate.

The handleOpenURL method returns a Boolean value indicating whether the URL was successfully handled:

• YES: The URL was handled, and you can use the provided data.
• NO: The URL could not be handled, and you should dismiss the URL loading request.

What Happens After handleOpenURL Returns

After calling handleOpenURL, your app delegate executes the following steps:

1. Load Data: If you’re using a dictionary as part of the URL’s contents, it’s loaded into an instance variable (e.g., theDictionary).
2. Configure and Show the Window: The app delegate configures and displays the main window.
3. Navigation Controller: The app delegate adds the navigation controller’s view to the window.

Passing Data Between Views

Now that we’ve discussed what happens when handleOpenURL returns, let’s explore ways to pass data between views in your iOS app:

Approach 1: Global Variables

One approach is to keep a global variable around to store and retrieve data. This can be useful for simple apps with limited complexity.

// AppDelegate.m

NSDictionary *sharedData = [[NSMutableDictionary alloc] init];

- (BOOL)application:(UIApplication *)application handleOpenURL:(NSURL *)url {
    // Load data from URL
    self.sharedData = [self sharedData];
    
    // Use the loaded data
    
    return YES;
}

Approach 2: Observer Pattern with Notification Center

The observer pattern is a design pattern that allows objects to be notified of changes in other objects. In this case, you can use the notification center to notify your view controllers when new data becomes available.

// AppDelegate.m

NSArray *observers = [NSMutableArray array];

- (BOOL)application:(UIApplication *)application handleOpenURL:(NSURL *)url {
    // Load data from URL
    NSDictionary *data = [self loadTestData];
    
    // Notify observers
    [[NSNotificationCenter defaultCenter] postNotificationName:@"newDataAvailable" object:nil userInfo:data];
    
    return YES;
}

Approach 3: NSUserDefaults

NSUserDefaults is a simple way to store and retrieve data between app launches. While it’s not as powerful as the observer pattern, it can be sufficient for small projects.

// AppDelegate.m

NSUserDefaults *sharedDefaults = [NSUserDefaults standardUserDefaults];

- (BOOL)application:(UIApplication *)application handleOpenURL:(NSURL *)url {
    // Load data from URL
    NSDictionary *data = [self loadTestData];
    
    // Store data in NSUserDefaults
    [sharedDefaults setObject:data forKey:@"myData"];
    
    return YES;
}

Approach 4: Subclassing WebViewCache

If you’re using UIWebView or WKWebview, you can subclass the cache and set a shared instance to retrieve data. This approach is useful when filtering URL data.

// CustomCache.h

#import <WebKit/WebKit.h>

@interface CustomCache : WKCache

+ (instancetype)sharedInstance;

@end

@implementation CustomCache

+ (instancetype)sharedInstance {
    static CustomCache *sharedInstance = nil;
    
    if (!sharedInstance) {
        sharedInstance = [[self alloc] init];
    }
    
    return sharedInstance;
}

- (BOOL)shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(WKNavigationType)navigationType {
    // Filter URL data here
    // ...
    return YES;
}

Conclusion

In this article, we explored the role of handleOpenURL and its return value in iOS applications. We also discussed approaches for passing data between views, including global variables, the observer pattern with notification center, NSUserDefaults, and subclassing WebViewCache.

By understanding how handleOpenURL works and choosing the right approach for your project, you can create a more robust and efficient app that handles custom URL schemes effectively.

Last modified on 2025-03-22