在UIScrollViewDelegate子类中实现UICollectionView

Question

我有一个UICollectionView子类。

我想为scrollViewDidScroll添加一个来自UIScrollViewDelegate的默认实现

有办法从scrollView子类访问UICollectionView委托方法吗？

谢谢

Answer 1

可以添加实现所需默认代码的函数，例如：

class YourCollectionView: UICollectionView {

    override init(frame: CGRect, collectionViewLayout layout: UICollectionViewLayout) {
        super.init(frame: frame, collectionViewLayout: layout)
    }

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

    func updateUIOnScrollViewDidScroll(_ scrollView: UIScrollView) {
        //...
    }
}

然后，在视图控制器中实现委托函数时，添加：

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    yourCollectionView.updateUIOnScrollViewDidScroll(scrollView)
}

编辑

如果您想像使用外部库一样使用您的集合，并且不希望每次调用更新的函数，则可以实现一个只符合UICollectionViewDelegate的自定义类(如果您想要的话，也可以有一个单独的CustomDataSource类来实现数据源和委托)，例如：

class YourCollectionViewDelegate: NSObject, UICollectionViewDelegate {
    // implement a callback for every function you need to manage in the view controller 
    var onSelectedItemAt: ((IndexPath) -> Void)?
    func collectionView(_ collectionView: UICollectionView, 
         didSelectItemAt indexPath: IndexPath) 
        onSelectedItemAt?(indexPath)
}

func scrollViewDidScroll(_ scrollView: UIScrollView) {
     guard let collectionView = scrollView as? YourCollectionViewClass else { fatalError(“your message”) }
    // implement your ui update 
}

然后，在视图控制器中，只需将委托与视图控制器绑定：

class MyViewController: UIViewController {

    //...
    let customDelegate = YourCollectionViewDelegate()

    override func viewDidLoad() {
         super.viewDidLoad()
        //...
        myCollection.delegate = customDelegate
        setupBindings()
    }

    private func setupBindings() {

        customDelegate.onSelectedItemAt = { [weak self] indexPath in 
            //...
        }
    }

Answer 2

只要用户滚动，我们就可以使用delegation概念从CustomCollectionView获得访问。

这是CustomCollectionView的实现，请注意，delegate方法是optional，在Objective C中是可用的。

这样，如果您的ViewController确认到CustomCollectionViewDelegate protocol，那么它就需要实现它不必实现的委托方法。

注：

然而，CustomCollectionView是UICollectionView的子类，意味着它的简单通用UI元素。实际上，它是View In Model-View-Controller (MVC)。根据MVC，View不能直接与Controller通信，View与Controller之间的通信是blind & structured。这种通信的好例子是Target & Action和delegate模式。

委托是一个简单的变量，包含在通用UI组件(如UIScrollView, UITableView, UICollectionView等)中。Controller必须通过将UI元素的delegate设置为self来确认协议，以便在其中实现委托方法。

结论是泛型UI元素的子类不能在其中实现委托方法。

但是，我们可以通过使用UIView制作一个定制的XIB并将collectionView添加到其中来实现这一点。

代码：

CustomCollectionView:

import UIKit

@objc protocol CustomCollectionViewDelegate {

    @objc optional func collectionViewDidScroll(_ scrollView: UIScrollView)
}

class CustomCollectionView: UIView {

    //MARK: - Outlets
    @IBOutlet weak var collection: UICollectionView!

    //MARK: - Variables
    weak var vc: UIViewController!
    weak var view: UIView!
    weak var customDelegate: CustomCollectionViewDelegate?

    let titles = ["HorizontalCollectionView", "VerticalCollectionView"]

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

    init(frame: CGRect, in vc: UIViewController, setCustomDelegate set: Bool) {
        super.init(frame: frame)
        xibSetup(frame: CGRect(x: 0, y: 0, width: frame.width, height: frame.height))
        self.vc = vc
        self.customDelegate = set ? vc as? CustomCollectionViewDelegate : nil
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        xibSetup(frame: CGRect(x: 0, y: 0, width: frame.width, height: frame.height))
    }

    private func xibSetup(frame: CGRect) {

        view = loadViewFromNib()
        view.frame = frame
        addSubview(view)

        collection.register(UINib(nibName: "CustomCollectionViewCell", bundle: nil), forCellWithReuseIdentifier: "CustomCollectionViewCell")
        collection.delegate = self
        collection.dataSource = self
    }

    private func loadViewFromNib() -> UIView {

        let bundle = Bundle(for: type(of: self))
        let nib = UINib(nibName: "CustomCollectionView", bundle: bundle)
        let view = nib.instantiate(withOwner: self, options: nil)[0] as! UIView

        return view
    }

}

extension CustomCollectionView: UIScrollViewDelegate {

    func scrollViewDidScroll(_ scrollView: UIScrollView) {

        if customDelegate != nil {
            customDelegate!.collectionViewDidScroll!(scrollView)
        }
    }
}

extension CustomCollectionView: UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {

        return titles.count
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {

        return UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {

        return 0
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {

        return 10 // Adjust the inter item space based on the requirement.
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

        return CGSize(width: 300, height: collectionView.bounds.height)
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "CustomCollectionViewCell", for: indexPath) as! CustomCollectionViewCell
        cell.titleLabel.text = titles[indexPath.row]
        return cell
    }
}

CustomCollectionView XIB:

<?xml version="1.0" encoding="UTF-8"?>
<document type="com.apple.InterfaceBuilder3.CocoaTouch.XIB" version="3.0" toolsVersion="14313.18" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" useSafeAreas="YES" colorMatched="YES">
    <device id="retina4_7" orientation="portrait">
        <adaptation id="fullscreen"/>
    </device>
    <dependencies>
        <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="14283.14"/>
        <capability name="Safe area layout guides" minToolsVersion="9.0"/>
        <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
    </dependencies>
    <objects>
        <placeholder placeholderIdentifier="IBFilesOwner" id="-1" userLabel="File's Owner" customClass="CustomCollectionView" customModule="SampleDemoApp" customModuleProvider="target">
            <connections>
                <outlet property="collection" destination="loF-CI-n5C" id="EZi-It-39z"/>
            </connections>
        </placeholder>
        <placeholder placeholderIdentifier="IBFirstResponder" id="-2" customClass="UIResponder"/>
        <view contentMode="scaleToFill" id="iN0-l3-epB" customClass="CustomCollectionView" customModule="SampleDemoApp" customModuleProvider="target">
            <rect key="frame" x="0.0" y="0.0" width="375" height="667"/>
            <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>
            <subviews>
                <collectionView clipsSubviews="YES" multipleTouchEnabled="YES" contentMode="scaleToFill" dataMode="none" translatesAutoresizingMaskIntoConstraints="NO" id="loF-CI-n5C">
                    <rect key="frame" x="0.0" y="0.0" width="375" height="667"/>
                    <color key="backgroundColor" white="1" alpha="1" colorSpace="custom" customColorSpace="genericGamma22GrayColorSpace"/>
                    <collectionViewFlowLayout key="collectionViewLayout" scrollDirection="horizontal" minimumLineSpacing="10" minimumInteritemSpacing="10" id="HQB-uW-7CY">
                        <size key="itemSize" width="50" height="50"/>
                        <size key="headerReferenceSize" width="0.0" height="0.0"/>
                        <size key="footerReferenceSize" width="0.0" height="0.0"/>
                        <inset key="sectionInset" minX="0.0" minY="0.0" maxX="0.0" maxY="0.0"/>
                    </collectionViewFlowLayout>
                </collectionView>
            </subviews>
            <color key="backgroundColor" red="1" green="1" blue="1" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
            <constraints>
                <constraint firstItem="loF-CI-n5C" firstAttribute="top" secondItem="iN0-l3-epB" secondAttribute="top" id="Khs-Aw-6b7"/>
                <constraint firstItem="loF-CI-n5C" firstAttribute="leading" secondItem="vUN-kp-3ea" secondAttribute="leading" id="cEr-al-Pib"/>
                <constraint firstItem="vUN-kp-3ea" firstAttribute="bottom" secondItem="loF-CI-n5C" secondAttribute="bottom" id="ftp-QG-OGJ"/>
                <constraint firstItem="vUN-kp-3ea" firstAttribute="trailing" secondItem="loF-CI-n5C" secondAttribute="trailing" id="num-9n-spN"/>
            </constraints>
            <viewLayoutGuide key="safeArea" id="vUN-kp-3ea"/>
            <point key="canvasLocation" x="138.40000000000001" y="153.37331334332833"/>
        </view>
    </objects>
</document>

ViewController:

override func viewDidLoad() {
    super.viewDidLoad()

    let collectionView = CustomCollectionView(frame: CGRect(x: 0, y: 0, width: UIScreen.main.bounds.width, height: 200), in: self, setCustomDelegate: true)
    view.addSubview(collectionView)
}

代理实现：

extension ViewController: CustomCollectionViewDelegate {

    func collectionViewDidScroll(_ scrollView: UIScrollView) {

        //do something...
    }
}