In Swift, how do I have a UIScrollView subclass that has an internal and external delegate?

Question

I\'m subclassing UIScrollView to add some features such as double tap to zoom and an image property for gallery purposes. But in order to do the image part my s

Answer 1

I don't know about any 100% Swift solution for this. Taking this ObjC answer to the same problem, and trying to port it to Swift it turns out that is not possible since NSInvocation is not available in Swift.

What we can do is to implement the suggested MyScrollViewPrivateDelegate in ObjC(don't forget to import it in the bridging header file) and the scroll view subclass in Swift like the following:

MyScrollView.swift

import UIKit

class MyScrollView: UIScrollView {

    private let myDelegate = MyScrollViewPrivateDelegate()

    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        super.delegate = myDelegate
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        super.delegate = myDelegate
    }

    override var delegate: UIScrollViewDelegate? {
        set {
            myDelegate.userDelegate = newValue
            super.delegate = nil
            super.delegate = myDelegate
        }

        get {
            return myDelegate.userDelegate
        }
    }

    func viewForZooming() -> UIView {
        return UIView()// return whatever you want here...
    }
}

MyScrollViewPrivateDelegate.h

#import 

@interface MyScrollViewPrivateDelegate : NSObject 

@property (weak, nonatomic) id userDelegate;

@end

MyScrollViewPrivateDelegate.m

#import "MyScrollViewPrivateDelegate.h"
#import "YOUR_MODULE-Swift.h"

@implementation MyScrollViewPrivateDelegate

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
    // you could check if the user delegate responds to viewForZoomingInScrollView and call it instead...
    return [(MyScrollView *)scrollView viewForZooming];
}

- (BOOL)respondsToSelector:(SEL)selector 
{
    return [_userDelegate respondsToSelector:selector] || [super respondsToSelector:selector];
}

- (void)forwardInvocation:(NSInvocation *)invocation 
{
    [invocation invokeWithTarget:_userDelegate];
}

@end