IOS obtains the sub-Controller on Interface Builder in two ways.

IOS obtains the sub-Controller on Interface Builder in two ways.

 

Preparations
On the Storyboard, drag and drop two sub-controllers for a ViewController, and set the identifiers of the two sews to childvc1 and childvc2 respectively.

Effect

Method 1: determine the result based on the identifier

#import ViewController.h#import ChildViewController1.h#import ChildViewController2.h@interface ViewController ()@property (weak,nonatomic)ChildViewController1 * childvc1;@property (weak,nonatomic)ChildViewController2 * childvc2;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    self.childvc1.view.backgroundColor = [UIColor blueColor];    self.childvc2.view.backgroundColor = [UIColor greenColor];    // Do any additional setup after loading the view, typically from a nib.}-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{    if ([segue.identifier isEqualToString:@childvc1]) {        self.childvc1 = segue.destinationViewController;    }    if ([segue.identifier isEqualToString:@childvc2]) {        self.childvc2 = segue.destinationViewController;    }}@end

Note:

PrepareForSegue is called earlier than viewDidLoad to use weak reference so that it does not participate in the lifecycle of the sub-controller. Method 2: Use the features of KVC to create some common code

#import ViewController.h#import ChildViewController1.h#import ChildViewController2.h@interface ViewController ()@property (weak,nonatomic)ChildViewController1 * childvc1;@property (weak,nonatomic)ChildViewController2 * childvc2;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    self.childvc1.view.backgroundColor = [UIColor blueColor];    self.childvc2.view.backgroundColor = [UIColor greenColor];    // Do any additional setup after loading the view, typically from a nib.}-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{    if ([self respondsToSelector:NSSelectorFromString(segue.identifier)]) {        [self setValue:segue.destinationViewController forKey:segue.identifier];    }}@end

Note:

The identifier must be consistent with the declared attributes of the corresponding sub-controller.

Principle-using the dynamic features of KVC

Because the property name of the sub-controller and segue. the identifer is consistent, so you only need to determine respondsToSelector: NSSelectorFromString (segue. identifier) to know whether the current is for the corresponding sub-controller to prepareForSegue the respondsToSelector: NSSelectorFromString (segue. identifier) is whether the corresponding get method is included and assigned by KVC.