iOS
Objective-Cでのランタイム

関連オブジェクトの使用

関連付けられたオブジェクトは、状態を保持する必要がある既存のクラスに機能を追加する場合に便利です。

たとえば、すべてのUIViewにアクティビティインジケータを追加します。

Objective-C実装

#import <objc/runtime.h>

static char ActivityIndicatorKey;

@implementation UIView (ActivityIndicator)

- (UIActivityIndicatorView *)activityIndicator {
    return (UIActivityIndicatorView *)objc_getAssociatedObject(self, &ActivityIndicatorKey);
}

- (void)setActivityIndicator: (UIActivityIndicatorView *)activityIndicator {
    objc_setAssociatedObject(self, &ActivityIndicatorKey, activityIndicator, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (void)showActivityIndicator {
    UIActivityIndicatorView *activityIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle: UIActivityIndicatorViewStyleGray];
    
    [self setActivityIndicator:activityIndicator];
    
    activityIndicator.center = self.center;
    activityIndicator.autoresizingMask = UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleBottomMargin;
    
    [activityIndicator startAnimating];
    
    [self addSubview: activityIndicator];
}

- (void)hideActivityIndicator {
    UIActivityIndicatorView * activityIndicator = [self activityIndicator];
    
    if (activityIndicator != nil) {
        [[self activityIndicator] removeFromSuperview];
    }
}

@end

Swiftを使用してObjective-Cランタイムにアクセスすることもできます。

スウィフトコード

extension UIView {
    private struct AssociatedKeys {
        static var activityIndicator = "UIView.ActivityIndicatorView"
    }

    private var activityIndicatorView: UIActivityIndicatorView? {
        get {
            return objc_getAssociatedObject(self, &AssociatedKeys.activityIndicator) as? UIActivityIndicatorView
        }
        set (activityIndicatorView) {
            objc_setAssociatedObject(self, &AssociatedKeys.activityIndicator, activityIndicatorView, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }

     func showActivityIndicator() {
        activityIndicatorView = UIActivityIndicatorView(activityIndicatorStyle: .gray)
        activityIndicatorView.center = center
        activityIndicatorView.autoresizingMask = [.flexibleLeftMargin, .flexibleRightMargin, .flexibleTopMargin, .flexibleBottomMargin]
        
        activityIndicatorView.startAnimating()
        
        addSubview(activityIndicatorView)
    }
    
    func hideActivityIndicator() {
        activityIndicatorView.removeFromSuperview()
    }
}