StateRestoreChildViews/ParentViewController.m

/*
     File: ParentViewController.m
 Abstract: The sample's primary/parent view controller
  Version: 1.1
 
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#import "ParentViewController.h"
#import "Child1ViewController.h"
#import "Child2ViewController.h"
 
@interface ParentViewController ()
 
@property (nonatomic, strong) IBOutlet UIView *placeholderView;
@property (nonatomic, strong) IBOutlet UISegmentedControl *segControl;
 
@property (nonatomic, strong) Child1ViewController *child1;
@property (nonatomic, strong) Child2ViewController *child2;
 
@end
 
@implementation ParentViewController
 
- (void)viewDidLoad
{
    [super viewDidLoad];
 
    self.navigationController.navigationBar.translucent = NO;
    
    // create and add our two children view controllers from our storyboard
    self.child1 = [self.storyboard instantiateViewControllerWithIdentifier:@"child1"];
    [self addChildViewController:self.child1];
    [self.child1 didMoveToParentViewController:self];
    
    self.child2 = [self.storyboard instantiateViewControllerWithIdentifier:@"child2"];
    [self addChildViewController:self.child2];
    [self.child2 didMoveToParentViewController:self];
    
    // by default child1 should be visible
    // (note that later, UIStateRestoriation might change this)
    //
    [self addChild:self.child1 withChildToRemove:nil];
}
 
- (void)addChild:(UIViewController *)childToAdd withChildToRemove:(UIViewController *)childToRemove
{
    assert(childToAdd != nil);
    
    if (childToRemove != nil)
    {
        [childToRemove.view removeFromSuperview];
    }
    
    // match the child size to its parent
    CGRect frame = childToAdd.view.frame;
    frame.size.height = CGRectGetHeight(self.placeholderView.frame);
    frame.size.width = CGRectGetWidth(self.placeholderView.frame);
    childToAdd.view.frame = frame;
    
    [self.placeholderView addSubview:childToAdd.view];
}
 
// user tapped on the segmented control to choose which child is to be visible
- (IBAction)segmentControlAction:(id)sender
{
    UISegmentedControl *segControl = (UISegmentedControl *)sender;
    
    UIViewController *childToAdd, *childToRemove;
    
    childToAdd = (segControl.selectedSegmentIndex == 0) ? self.child1 : self.child2;
    childToRemove = (segControl.selectedSegmentIndex == 0) ? self.child2 : self.child1;
    
    [self addChild:childToAdd withChildToRemove:childToRemove];
}
 
 
#pragma mark - UIStateRestoration
 
// encodeRestorableStateWithCoder is called when the app is suspended to the background
- (void)encodeRestorableStateWithCoder:(NSCoder *)coder
{
    NSLog(@"ParentViewController: encodeRestorableStateWithCoder");
    
    // remember our children view controllers
    [coder encodeObject:self.child1 forKey:@"child1"];
    [coder encodeObject:self.child2 forKey:@"child2"];
    
    // remember the segmented control state
    [coder encodeInteger:self.segControl.selectedSegmentIndex forKey:@"selectedIndex"];
    
    [super encodeRestorableStateWithCoder:coder];
}
 
// decodeRestorableStateWithCoder is called when the app is re-launched
- (void)decodeRestorableStateWithCoder:(NSCoder *)coder
{
    NSLog(@"ParentViewController: decodeRestorableStateWithCoder");
    
    // find out which child was the current visible view controller
    self.segControl.selectedSegmentIndex = [coder decodeIntegerForKey:@"selectedIndex"];
    
    // call our segmented control to set the right visible child
    // (note that we already previously have already loaded both children view controllers in viewDidLoad)
    //
    [self segmentControlAction:self.segControl];
    
    [super decodeRestorableStateWithCoder:coder];
}
 
@end