コードからもIBからも使えるUIViewのサブクラスのinitに関して ref: https://qiita.com/sasau/items/9dd4e1c78ee669603ddb

file0.txt

@interface HogeView: UIView

@property(nonatomic)UIView *fugaView;

@end

@implementation HogeView

- (instancetype)initWithFrame:(CGFrame)frame {
    self = [super initWithFrame:frame];
    if(self) {
        [self setup];        
    }
    return self;
}

- (instancetype)initWithCoder:(NSCoder *)aDecoder {
    self = [super initWithCoder:aDecoder];
    if(self) {
        [self setup];
    }
    return self;
}

- (void)setup {
    self.fugaView = [UIView new];
    [self addSubview:self.fugaView];
}
@end

file1.swift

class HogeView: UIView {
    let fugaView: UIView

    init(_ coder: NSCoder? = nil) {
        // common initialize
        fugaView = UIView.init()

        if let coder = coder {
            super.init(coder: coder)!
        } else {
            super.init(frame: CGRect.zero)
        }

        // common setup
       addSubview(fugaView)
    }

    required convenience init?(coder aDecoder: NSCoder) {
        self.init(aDecoder)
    }
}