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floriankugler committed Jun 5, 2015
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131 changes: 74 additions & 57 deletions 2013-06-07-containment-view-controller.md
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Expand Up @@ -2,7 +2,9 @@
title: "View Controller Containment"
category: "1"
date: "2013-06-07 08:00:00"
author: "<a href=\"https://twitter.com/rickigregersen\">Ricki Gregersen</a>"
author:
- name: Ricki Gregersen
url: https://twitter.com/rickigregersen
tags: article
---

Expand All @@ -16,10 +18,12 @@ This has since changed to <q>a view controller manages a self-contained
unit of content</q>.
Why didn't Apple want us to build our own tab bar controllers and
navigation controllers? Or put more precisely, what is the problem with:

[viewControllerA.view addSubView:viewControllerB.view]

<img src="/images/issue-1/[email protected]" style="width:357px" alt="Inconsistent view hierarchy"/>
```objc
[viewControllerA.view addSubView:viewControllerB.view]
```
![Inconsistent view hierarchy](/images/issue-1/[email protected])
The UIWindow, which serves as an app's root view, is where rotation and
initial layout messages originate from. In the
Expand All @@ -41,7 +45,7 @@ repo](https://github.com/objcio/issue-1-view-controller-containment) and run the
app, which will make it easier to understand the example code.
*(Spoiler: digging through the earth from western Denmark lands you somewhere in the South Pacific Ocean.)*
<img src="/images/issue-1/[email protected]" alt="Tunnel screenshot" style="width: 513px;" />
![Tunnel screenshot](/images/issue-1/[email protected])
To find the antipode, as the opposite location is called, move the little guy with the shovel around and the map will tell you where your exit location is. Tap the radar button and the map will flip to reveal the name of the location.
Expand All @@ -53,23 +57,25 @@ The root view controller has two container views. These are added to
make it easier to layout and animate the views of child view
controllers, as we will see later on.
- (void)viewDidLoad
{
[super viewDidLoad];

//Setup controllers
_startMapViewController = [RGMapViewController new];
[_startMapViewController setAnnotationImagePath:@"man"];
[self addChildViewController:_startMapViewController]; // 1
[topContainer addSubview:_startMapViewController.view]; // 2
[_startMapViewController didMoveToParentViewController:self]; // 3
[_startMapViewController addObserver:self
forKeyPath:@"currentLocation"
options:NSKeyValueObservingOptionNew
context:NULL];

_startGeoViewController = [RGGeoInfoViewController new]; // 4
}
```objc
- (void)viewDidLoad
{
[super viewDidLoad];
//Setup controllers
_startMapViewController = [RGMapViewController new];
[_startMapViewController setAnnotationImagePath:@"man"];
[self addChildViewController:_startMapViewController]; // 1
[topContainer addSubview:_startMapViewController.view]; // 2
[_startMapViewController didMoveToParentViewController:self]; // 3
[_startMapViewController addObserver:self
forKeyPath:@"currentLocation"
options:NSKeyValueObservingOptionNew
context:NULL];
_startGeoViewController = [RGGeoInfoViewController new]; // 4
}
```

The `_startMapViewController`, which displays the starting position, is instantiated and set up with the annotation image.

Expand All @@ -90,15 +96,17 @@ which determine the size of the child view controllers.
The child view controllers do not know which container they will be
added to, and therefore have to be flexible in size:

- (void) loadView
{
mapView = [MKMapView new];
mapView.autoresizingMask = UIViewAutoresizingFlexibleWidth |UIViewAutoresizingFlexibleHeight;
[mapView setDelegate:self];
[mapView setMapType:MKMapTypeHybrid];

self.view = mapView;
}
```objc
- (void) loadView
{
mapView = [MKMapView new];
mapView.autoresizingMask = UIViewAutoresizingFlexibleWidth |UIViewAutoresizingFlexibleHeight;
[mapView setDelegate:self];
[mapView setMapType:MKMapTypeHybrid];

self.view = mapView;
}
```

Now they will layout using the bounds of their super view. This increases the reusability of the child view controller; if we were to push it on the stack of a navigation controller, it would still layout correctly.

Expand All @@ -112,25 +120,27 @@ The method
`transitionFromViewController:toViewController:(...)`
takes care of a lot of the details for us:

- (void) flipFromViewController:(UIViewController*) fromController
toViewController:(UIViewController*) toController
withDirection:(UIViewAnimationOptions) direction
{
toController.view.frame = fromController.view.bounds; // 1
[self addChildViewController:toController]; //
[fromController willMoveToParentViewController:nil]; //
[self transitionFromViewController:fromController
toViewController:toController
duration:0.2
options:direction | UIViewAnimationOptionCurveEaseIn
animations:nil
completion:^(BOOL finished) {
[toController didMoveToParentViewController:self]; // 2
[fromController removeFromParentViewController]; // 3
}];
}
```objc
- (void) flipFromViewController:(UIViewController*) fromController
toViewController:(UIViewController*) toController
withDirection:(UIViewAnimationOptions) direction
{
toController.view.frame = fromController.view.bounds; // 1
[self addChildViewController:toController]; //
[fromController willMoveToParentViewController:nil]; //

[self transitionFromViewController:fromController
toViewController:toController
duration:0.2
options:direction | UIViewAnimationOptionCurveEaseIn
animations:nil
completion:^(BOOL finished) {
[toController didMoveToParentViewController:self]; // 2
[fromController removeFromParentViewController]; // 3
}];
}
```

1. Before the animation we add the `toController` as a child and we
inform the `fromController` that it will be removed. If the fromController's view is part of the container's view hierarchy, this is where `viewWillDisappear:` is called.
Expand All @@ -152,18 +162,25 @@ Child view controllers should contain the necessary logic to manage their view t

In the Tunnel example app, the parent view controller observes a property called `currentLocation` on the map view controllers:

[_startMapViewController addObserver:self
forKeyPath:@"currentLocation"
options:NSKeyValueObservingOptionNew
context:NULL];
```objc
[_startMapViewController addObserver:self
forKeyPath:@"currentLocation"
options:NSKeyValueObservingOptionNew
context:NULL];
```
When this property changes in response to moving the little guy with the shovel around on the map, the parent view controller communicates the antipode of the new location to the other map:
[oppositeController updateAnnotationLocation:[newLocation antipode]];
```objc
[oppositeController updateAnnotationLocation:[newLocation antipode]];
```


Likewise, when you tap the radar button, the parent view controller sets the locations to be reverse geocoded on the new child view controllers:

[_startGeoViewController setLocation:_startMapViewController.currentLocation];
[_targetGeoViewController setLocation:_targetMapViewController.currentLocation];
```objc
[_startGeoViewController setLocation:_startMapViewController.currentLocation];
[_targetGeoViewController setLocation:_targetMapViewController.currentLocation];
```
Independent of the technique you choose to communicate from child to parent view controllers (KVO, notifications, or the delegate pattern), the goal always stays the same: the child view controllers should be independent and reusable. In our example we could push one of the child view controllers on a navigation stack, but the communication would still work through the same API.
5 changes: 0 additions & 5 deletions 2013-06-07-index.markdown
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