Ios – How does View Controller Containment work in iOS 5

iosios5uiviewcontroller

In WWDC 2011 Session 102, Apple introduced View Controller Containment, which is the ability to create custom view controller containers, analogous to UITabBarController, UINavigationController, and the like.

I watched the examples several times. There are a flurry of methods associated with this pattern, but it was a little hard to figure them out exactly. I'm going to post here what I think is going on and see if the community will confirm or disconfirm my suspicions.

Scenario 1: Moving from no parent to a new parent view controller

[vc willMoveToParentViewController:self];
[self addChildViewController:vc];
[self.view addSubview:vc.view]; // or something like this.
[vc didMoveToParentViewController:self];

Do the first two lines have to occur in the order given, or can they be reversed?

Scenario 2: Moving from a parent view controller to no parent view controller

[vc willMoveToParentViewController:nil];
[vc.view removeFromSuperview];
[vc removeFromParentViewController];

Is it also necessary to call [vc didMoveToParentViewController:nil]? The examples in Session 102 did not do this in this scenario, but I don't know whether that was an omission or not.

Scenario 3: Moving from one parent view controller to another

This will likely occur in the following way, because the logic in each parent view controller will be encapsulated.

// In the old parent
[vc willMoveToParentViewController:nil];
[vc.view removeFromSuperview];
[vc removeFromParentViewController];

// In the new parent
[vc willMoveToParentViewController:self];
[self addChildViewController:vc];
[self.view addSubview:vc.view];
[vc didMoveToParentViewController:self];

Questions

My main question is this: Is this how view controller containment should work, in general? Are the mechanics given above correct?

Is it necessary to call willMoveToParentViewController before calling addChildViewController? This seems like the logical order to me, but is it strictly necessary?

Is it necessary to call didMoveToParentViewController:nil after calling removeFromParentViewController?

Best Answer

The UIViewController docs are pretty clear on when and when not to call willMove/didMove methods. Check out the "Implementing a Container View Controller" documentation.

The docs say, that if you do not override addChildViewController, you do not have to call willMoveToParentViewController: method. However you do need to call the didMoveToParentViewController: method after the transition is complete. "Likewise, it is is the responsibility of the container view controller to call the willMoveToParentViewController: method before calling the removeFromParentViewController method. The removeFromParentViewController method calls the didMoveToParentViewController: method of the child view controller."

Also, there is an example worked out here and sample code here.

Good Luck

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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