无限滚动TableView

InfiniteTableView.swift

//
//  InfiniteTableView.swift
//  EShopHelper
//
//  Created by Jiang,Zhenhua on 2018/12/1.
//  Copyright © 2018 Daubert. All rights reserved.
//

import UIKit

class InfiniteTableView: UITableView {

    class Interceptor: NSObject, UITableViewDataSource {
        
        weak var receiver: UITableViewDataSource!
        weak var middleman: UITableView?
        private var actualRows = 0
        
        override func forwardingTarget(for aSelector: Selector!) -> Any? {
            if let middleman = middleman, middleman.responds(to: aSelector) {
                return middleman
            }
            if let receiver = receiver, receiver.responds(to: aSelector) {
                return receiver
            }
            return super.forwardingTarget(for: aSelector)
        }
        
        override func responds(to aSelector: Selector!) -> Bool {
            if let middleman = middleman, middleman.responds(to: aSelector) {
                return true
            }
            if let receiver = receiver, receiver.responds(to: aSelector) {
                return true
            }
            return super.responds(to: aSelector)
        }
        
        func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
            actualRows = receiver.tableView(tableView, numberOfRowsInSection: section)
            return actualRows * 3
        }
        
        func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
            let actualIndexPath = IndexPath(row: indexPath.row % actualRows, section: indexPath.section)
            return receiver.tableView(tableView, cellForRowAt: actualIndexPath)
        }
    }

    private lazy var dataSourceInterceptor: Interceptor = {
        let interceptor = Interceptor()
        interceptor.middleman = self
        return interceptor
    }()
    
    override func layoutSubviews() {
        resetContentOffsetIfNeeded()
        super.layoutSubviews()
    }
    
    private func resetContentOffsetIfNeeded() {
        var contentOffset = self.contentOffset
        if contentOffset.y < 0 {// scroll over top
            contentOffset.y = contentSize.height / 3
        } else if contentOffset.y >= contentSize.height - bounds.size.height { // scroll over bottom
            contentOffset.y = contentSize.height / 3 - bounds.size.height
        }
        self.contentOffset = contentOffset
    }
    
    override var dataSource: UITableViewDataSource? {
        set(dataSource) {
            dataSourceInterceptor.receiver = dataSource
        }
        get {
            return dataSourceInterceptor
        }
    }
}