iOS 获取Interface Builder上的子控制器的两种方式

原创Blog，转载请注明出处
blog.youkuaiyun.com/hello_hwc

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准备工作
Storyboard上为一个ViewController拖拽两个子控制器，并且设置两个segue的identifier分别为childvc1,childvc2

效果

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方式一，根据segue的identifier来判断获得

#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

两点要注意

1. prepareForSegue在这里要早于viewDidLoad被调用
2. 使用weak引用是为了不参与子控制器的生命周期

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方式二，借助KVC的特性，创建一些通用的代码

#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

注意，这里的

segue的identifier一定要和声明的对应子控制器的属性一致。

原理－利用KVC的动态特性

1. 因为子控制器的属性名称与segue.identifer一致，所以只需要判断respondsToSelector:NSSelectorFromString(segue.identifier)就知道当前是不是为对应的子控制器来prepareForSegue
2. 这里的 respondsToSelector:NSSelectorFromString(segue.identifier)就是是否含有对应的get方法
3. 通过KVC的方式进行赋值

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