Question

我正在对UIScrollView进行子类化以添加一些功能，例如双击缩放和图库属性以用于图库目的。但是为了做图像部分，我的子类必须是它自己的委托并实现viewForZoomingInScrollView。

但是当有人使用我的滚动视图子类时，他们可能也希望获得委托通知以查看scrollViewDidScroll或你有什么。

在Swift中，我如何获得这两个？

Answer 1

以下是此模式的Swift版本：

虽然在Swift中禁用了forwardInvocation:，但我们仍然可以使用forwardingTargetForSelector:

class MyScrollView: UIScrollView {

    class _DelegateProxy: NSObject, UIScrollViewDelegate {
        weak var _userDelegate: UIScrollViewDelegate?

        override func respondsToSelector(aSelector: Selector) -> Bool {
            return super.respondsToSelector(aSelector) || _userDelegate?.respondsToSelector(aSelector) == true
        }

        override func forwardingTargetForSelector(aSelector: Selector) -> AnyObject? {
            if _userDelegate?.respondsToSelector(aSelector) == true {
                return _userDelegate
            }
            else {
                return super.forwardingTargetForSelector(aSelector)
            }
        }

        func viewForZoomingInScrollView(scrollView: MyScrollView) -> UIView? {
            return scrollView.viewForZooming()
        }

        // Just a demo. You don't need this.
        func scrollViewDidScroll(scrollView: MyScrollView) {
            scrollView.didScroll()
            _userDelegate?.scrollViewDidScroll?(scrollView)
        }
    }

    private var _delegateProxy =  _DelegateProxy()

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

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

    override var delegate:UIScrollViewDelegate? {
        get {
            return _delegateProxy._userDelegate
        }
        set {
            self._delegateProxy._userDelegate = newValue;
            /* It seems, we don't need this anymore.
            super.delegate = nil
            super.delegate = _delegateProxy
            */
        }
    }

    func viewForZooming() -> UIView? {
        println("self viewForZooming")
        return self.subviews.first as? UIView // whatever
    }

    func didScroll() {
        println("self didScroll")
    }
}

Answer 2

这是Swift 3中一个简单的Playground版本，它纯粹作为一个观察者，而不仅仅是像其他答案一样的拦截器。

区别在于原始滚动视图委托应该将其所有委托方法调用为正常，而不是被另一个委托劫持。

（您可以将其复制/粘贴到游乐场并运行以进行测试）

import UIKit

final class ScrollViewObserver: NSObject, UIScrollViewDelegate {

    // MARK: - Instantiation

    init(scrollView: UIScrollView) {
        super.init()

        self.scrollView = scrollView
        self.originalScrollDelegate = scrollView.delegate
        scrollView.delegate = self
    }

    deinit {
        self.remove()
    }

    // MARK: - API

    /// Removes ourselves as an observer, resetting the scroll view's original delegate
    func remove() {
        self.scrollView?.delegate = self.originalScrollDelegate
    }

    // MARK: - Private Properties

    fileprivate weak var scrollView: UIScrollView?
    fileprivate weak var originalScrollDelegate: UIScrollViewDelegate?

    // MARK: - Forwarding Delegates

    /// Note: we forward all delegate calls here since Swift does not support forwardInvocation: or NSProxy

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        // Run any custom logic or send any notifications here
        print("proxy did scroll")

        // Then, forward the call to the original delegate
        self.originalScrollDelegate?.scrollViewDidScroll?(scrollView)
    }

    func scrollViewDidZoom(_ scrollView: UIScrollView) {
        self.originalScrollDelegate?.scrollViewDidZoom?(scrollView)
    }

    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        self.originalScrollDelegate?.scrollViewWillBeginDragging?(scrollView)
    }

    func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
        self.originalScrollDelegate?.scrollViewWillEndDragging?(scrollView, withVelocity: velocity, targetContentOffset: targetContentOffset)
    }

    func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        self.originalScrollDelegate?.scrollViewDidEndDragging?(scrollView, willDecelerate: decelerate)
    }

    func scrollViewWillBeginDecelerating(_ scrollView: UIScrollView) {
        self.originalScrollDelegate?.scrollViewWillBeginDecelerating?(scrollView)
    }

    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        self.originalScrollDelegate?.scrollViewDidEndDecelerating?(scrollView)
    }

    func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
        self.originalScrollDelegate?.scrollViewDidEndScrollingAnimation?(scrollView)
    }

    func viewForZooming(in scrollView: UIScrollView) -> UIView? {
        return self.originalScrollDelegate?.viewForZooming?(in: scrollView)
    }

    func scrollViewWillBeginZooming(_ scrollView: UIScrollView, with view: UIView?) {
        self.originalScrollDelegate?.scrollViewWillBeginZooming?(scrollView, with: view)
    }

    func scrollViewDidEndZooming(_ scrollView: UIScrollView, with view: UIView?, atScale scale: CGFloat) {
        self.originalScrollDelegate?.scrollViewDidEndZooming?(scrollView, with: view, atScale: scale)
    }

    func scrollViewShouldScrollToTop(_ scrollView: UIScrollView) -> Bool {
        return self.originalScrollDelegate?.scrollViewShouldScrollToTop?(scrollView) == true
    }

    func scrollViewDidScrollToTop(_ scrollView: UIScrollView) {
        self.originalScrollDelegate?.scrollViewDidScrollToTop?(scrollView)
    }

}

final class TestView: UIView, UIScrollViewDelegate {

    let scrollView = UIScrollView()
    fileprivate(set) var scrollObserver: ScrollViewObserver?

    required init() {
        super.init(frame: .zero)

        self.scrollView.delegate = self
        self.scrollObserver = ScrollViewObserver(scrollView: self.scrollView)
    }

    required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    public func scrollViewDidScroll(_ scrollView: UIScrollView) {
        print("view's original did scroll delegate method called")
    }

}

let testView = TestView()
testView.scrollView.setContentOffset(CGPoint(x: 0, y: 100), animated: true)
testView.scrollObserver?.remove()
print("removed the observer")
testView.scrollView.setContentOffset(CGPoint(x: 0, y: 200), animated: true)
testView.scrollView.setContentOffset(CGPoint(x: 0, y: 300), animated: true)

打印

代理滚动了

view的原始做了名为
的滚动委托方法
删除了观察者

view的原始做了名为
的滚动委托方法
view的原始做了名为
的滚动委托方法

Answer 3

我不知道任何100％Swift解决方案。将this ObjC answer置于同一问题，并尝试将其移植到Swift，结果证明这是不可能的，因为NSInvocation在Swift中不可用。

我们可以做的是在ObjC中实现建议的MyScrollViewPrivateDelegate（不要忘记在桥接头文件中导入它）和Swift中的滚动视图子类，如下所示：

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 <UIKit/UIKit.h>

@interface MyScrollViewPrivateDelegate : NSObject <UIScrollViewDelegate>

@property (weak, nonatomic) id<UIScrollViewDelegate> 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

Answer 4

rintaro's excellent answer的4+版本：

class MyScrollView: UIScrollView {
    class _DelegateProxy: NSObject, UIScrollViewDelegate {
        weak var _userDelegate: UIScrollViewDelegate?

        override func responds(to aSelector: Selector!) -> Bool {
            return super.responds(to: aSelector) || _userDelegate?.responds(to: aSelector) == true
        }

        override func forwardingTarget(for aSelector: Selector!) -> Any? {
            if _userDelegate?.responds(to: aSelector) == true {
                return _userDelegate
            }

            return super.forwardingTarget(for: aSelector)
        }

        //This function is just a demonstration, it can be replaced/removed.
        func scrollViewDidScroll(_ scrollView: UIScrollView) {
            (scrollView as? MyScrollView)?.didScroll()

            _userDelegate?.scrollViewDidScroll?(scrollView)
        }
    }

    fileprivate let _delegateProxy = _DelegateProxy()

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        super.delegate = _delegateProxy
    }

    override init(frame: CGRect) {
        super.init(frame: frame)

        super.delegate = _delegateProxy
    }

    override var delegate: UIScrollViewDelegate? {
        get {
            return _delegateProxy._userDelegate
        }

        set {
            _delegateProxy._userDelegate = newValue
        }
    }

    func didScroll() {
        print("didScroll")
    }
}

在Swift中，我如何拥有一个具有内部和外部委托的UIScrollView子类？

4 个答案: