Ios – How to tell the active view controller when applicationDidBecomeActive is called

iosiphoneswiftxcode-storyboard

I feel I am missing a trick here…

I just want to call viewDidLoad or viewDidAppear on the current active view controller when applicationDidBecomeActive gets called, so I can reset some animations or whatever, when the app is started up again from the background. Some of my views don't care, but others really need to know.

I am using Storyboards and my app delegate file has the standard functions – but all with EMPTY bodies. For example, didFinishLaunchingWithOptions just returns YES and does nothing else. Storyboard automagically does everything I guess.

So how can I talk to the current view controller from my rather blank, information free, app delegate?

Best Answer

Instead of sending a notification from your app delegate, the OS sends a notification automatically that you can observe:

[[NSNotificationCenter defaultCenter] addObserver:self
                                      selector:@selector(initSongInfo)
                                      name:UIApplicationDidBecomeActiveNotification
                                      object:nil];

and of course make sure to stop observing sometime before or inside your dealloc method, by calling:

[[NSNotificationCenter defaultCenter] removeObserver:self 
                                      name:UIApplicationDidBecomeActiveNotification 
                                      object:nil];

Swift

Install via CocoaPods or Carthage: https://github.com/ashleymills/Reachability.swift

Test reachability via closures

let reachability = Reachability()!

reachability.whenReachable = { reachability in
    if reachability.connection == .wifi {
        print("Reachable via WiFi")
    } else {
        print("Reachable via Cellular")
    }
}

reachability.whenUnreachable = { _ in
    print("Not reachable")
}

do {
    try reachability.startNotifier()
} catch {
    print("Unable to start notifier")
}

Objective-C

Add SystemConfiguration framework to the project but don't worry about including it anywhere
Add Tony Million's version of Reachability.h and Reachability.m to the project (found here: https://github.com/tonymillion/Reachability)

Update the interface section

#import "Reachability.h"

// Add this to the interface in the .m file of your view controller
@interface MyViewController ()
{
    Reachability *internetReachableFoo;
}
@end

Then implement this method in the .m file of your view controller which you can call

// Checks if we have an internet connection or not
- (void)testInternetConnection
{
    internetReachableFoo = [Reachability reachabilityWithHostname:@"www.google.com"];

    // Internet is reachable
    internetReachableFoo.reachableBlock = ^(Reachability*reach)
    {
        // Update the UI on the main thread
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"Yayyy, we have the interwebs!");
        });
    };

    // Internet is not reachable
    internetReachableFoo.unreachableBlock = ^(Reachability*reach)
    {
        // Update the UI on the main thread
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"Someone broke the internet :(");
        });
    };

    [internetReachableFoo startNotifier];
}

Important Note: The Reachability class is one of the most used classes in projects so you might run into naming conflicts with other projects. If this happens, you'll have to rename one of the pairs of Reachability.h and Reachability.m files to something else to resolve the issue.

Note: The domain you use doesn't matter. It's just testing for a gateway to any domain.

Best Answer

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Swift

Objective-C

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