ios - 如何让 tableFooterView 始终位于 UITableView 的底部

Question

我有一个包含可变数量部分的 UITableView。每个部分都有可变数量的单元格，每个部分都有页眉和页脚。我的 UITableView 也有一个 tableFooterView，我希望它始终位于屏幕底部，除非表格太大而无法显示在屏幕上，然后tableFooterView 应显示在最后一部分下方。我想要完成的事情如下所示:

Example of what I want, scenario 1

Example of what I want, scenario 2

但是，目前 tableFooterView 始终位于最后一部分的正下方，因此当只有两部分时，它看起来像这样:

Example of what I currently have

我正在寻找一种方法，使其在所有可能的情况下始终保持在底部。我一直在四处寻找，因为 Apple 不支持 tableFooterView 的 AutoLayout，所以我还没有找到解决方案。类似的情况是在最后一节用 sectionFooter 替换 tableFooterView，但我不能这样做，因为我已经有了 sectionFooters。

有没有人可以帮助我或指出正确的方向？需要考虑的几件事:

• 它必须是一个tableFooterView；
• 用户可以向 UITableView 添加部分并向部分添加行，因此 tableFooterView 应该更新其位置

我目前如何设置 tableFooterView:

class CustomView: UITableViewDelegate, UITableViewDataSource {

    var myTableFooter: UIView = {

        let myTableFooter = UIView(frame: CGRect(x: 0, y: 0, width: UIScreen.main.bounds.width, height: 50))
        myTableFooter.backgroundColor = .red
        myTableFooter.isUserInteractionEnabled = true
        return myTableFooter

    }()

    override init(frame: CGRect) {

        super.init(frame: frame)
        setupViews()

        MyTableView.tableFooterView = myTableFooter

    }

}

编辑:按照建议尝试了 scrollViewDidScroll 方法，但没有成功:

func scrollViewDidScroll(_ scrollView: UIScrollView) {

    if(scrollView == myTableView) {

        let neededHeight = myTableView.frame.height - 50 - view.safeAreaInsets.bottom
        let currentHeight = myTableView.contentSize.height - 50

        let heightDifference = neededHeight - currentHeight

        if(heightDifference > 0) {

            myTableView.tableFooterView?.transform = CGAffineTransform(translationX: 0, y: heightDifference)

        }

    }

}

Answer 1

一种方法是:

• 使用扩展来定义“自适应非滚动”表格 View
• 在“容器” View 中为“页脚” View 嵌入 TableView 和普通UIView
• 将容器 View 嵌入到 ScrollView 中，高度与 ScrollView 相同，但优先级较低
• 将页脚 View 限制在容器 View 的底部，并将 >= 限制在 TableView 的底部

所以，tableView的“auto-height”+footer view的高度决定了container view的高度，进而决定了scroll view的.contentSize。页脚 View 将“粘贴”到容器 View 的底部。当 ScrollView 有足够的内容时，它将“下推”页脚 View 。

例子:

这是创建它的代码。一切都是通过代码完成的……不需要 IBOutlets，所以只需创建一个新的 View Controller 并将其类分配给 PennyWiseViewController:

//
//  PennyWiseViewController.swift
//
//  Created by Don Mag on 5/14/19.
//

import UIKit

final class ContentSizedTableView: UITableView {

    override var contentSize:CGSize {
        didSet {
            invalidateIntrinsicContentSize()
        }
    }

    override var intrinsicContentSize: CGSize {
        layoutIfNeeded()
        return CGSize(width: UIView.noIntrinsicMetric, height: contentSize.height)
    }

}

class MyOneLabelCell: UITableViewCell {

    // very simple one-label tableView cell

    let theLabel: UILabel = {
        let v = UILabel()
        v.translatesAutoresizingMaskIntoConstraints = false
        v.numberOfLines = 0
        return v
    }()

    override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {
        super.init(style: style, reuseIdentifier: reuseIdentifier)

        contentView.addSubview(theLabel)

        NSLayoutConstraint.activate([
            theLabel.topAnchor.constraint(equalTo: contentView.topAnchor, constant: 8.0),
            theLabel.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -8.0),
            theLabel.leadingAnchor.constraint(equalTo: contentView.leadingAnchor, constant: 8.0),
            theLabel.trailingAnchor.constraint(equalTo: contentView.trailingAnchor, constant: -8.0),
            ])

    }

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

}

class PennyWiseViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {

    let theContainerView: UIView = {
        let v = UIView()
        v.translatesAutoresizingMaskIntoConstraints = false
        return v
    }()

    let theScrollView: UIScrollView = {
        let v = UIScrollView()
        v.translatesAutoresizingMaskIntoConstraints = false
        return v
    }()

    let theTableView: ContentSizedTableView = {
        let v = ContentSizedTableView()
        v.translatesAutoresizingMaskIntoConstraints = false
        v.isScrollEnabled = false
        return v
    }()

    let theFooterView: UILabel = {
        let v = UILabel()
        v.translatesAutoresizingMaskIntoConstraints = false
        v.backgroundColor = .red
        v.textColor = .white
        v.text = "The Footer View"
        v.textAlignment = .center
        return v
    }()

    // start with 3 sections
    // selecting the row in the first section allows adding sections
    // selecting the row in the second section allows deleting sections
    var numSections = 3

    let reuseID = "MyOneLabelCell"

    override func viewDidLoad() {
        super.viewDidLoad()

        theTableView.dataSource = self
        theTableView.delegate = self

        theTableView.register(MyOneLabelCell.self, forCellReuseIdentifier: reuseID)

        // add the views
        view.addSubview(theScrollView)
        theScrollView.addSubview(theContainerView)
        theContainerView.addSubview(theTableView)
        theContainerView.addSubview(theFooterView)

        // this will allow the container height to be at least the height of the scroll view
        // when enough content is added to the container, it will grow
        let containerHeightConstraint = theContainerView.heightAnchor.constraint(equalTo: theScrollView.heightAnchor, multiplier: 1.0)
        containerHeightConstraint.priority = .defaultLow

        NSLayoutConstraint.activate([

            // constrain scrollView to all 4 sides (safe-area)
            theScrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
            theScrollView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor),
            theScrollView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor),
            theScrollView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor),

            // constrain containerView to all 4 sides of scrollView
            theContainerView.topAnchor.constraint(equalTo: theScrollView.topAnchor),
            theContainerView.bottomAnchor.constraint(equalTo: theScrollView.bottomAnchor),
            theContainerView.leadingAnchor.constraint(equalTo: theScrollView.leadingAnchor),
            theContainerView.trailingAnchor.constraint(equalTo: theScrollView.trailingAnchor),

            theContainerView.widthAnchor.constraint(equalTo: theScrollView.widthAnchor),

            // constrain tableView to top/leading/trailing of constainerView
            theTableView.topAnchor.constraint(equalTo: theContainerView.topAnchor),
            theTableView.leadingAnchor.constraint(equalTo: theContainerView.leadingAnchor),
            theTableView.trailingAnchor.constraint(equalTo: theContainerView.trailingAnchor),

            // constrain footerView >= 20 from bottom of tableView
            theFooterView.topAnchor.constraint(greaterThanOrEqualTo: theTableView.bottomAnchor, constant: 20.0),

            theFooterView.leadingAnchor.constraint(equalTo: theContainerView.leadingAnchor, constant: 0.0),
            theFooterView.trailingAnchor.constraint(equalTo: theContainerView.trailingAnchor, constant: 0.0),
            theFooterView.bottomAnchor.constraint(equalTo: theContainerView.bottomAnchor, constant: 0.0),

            theFooterView.heightAnchor.constraint(equalToConstant: 150.0),

            containerHeightConstraint,

            ])

    }


    // MARK: - Table view data source

    func numberOfSections(in tableView: UITableView) -> Int {
        return numSections
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return section < 2 ? 1 : 2
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: reuseID, for: indexPath) as! MyOneLabelCell

        switch indexPath.section {
        case 0:
            cell.theLabel.text = "Add a section"
        case 1:
            cell.theLabel.text = "Delete a section"
        default:
            cell.theLabel.text = "\(indexPath)"
        }

        return cell
    }

    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        tableView.deselectRow(at: indexPath, animated: true)

        switch indexPath.section {
        case 0:
            numSections += 1
            tableView.reloadData()
        case 1:
            if numSections > 2 {
                numSections -= 1
                tableView.reloadData()
            }
        default:
            print("\(indexPath) was selected")
        }

    }

    func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
        return "Section \(section) Header"
    }

    func tableView(_ tableView: UITableView, titleForFooterInSection section: Int) -> String? {
        return "Section \(section) Footer"
    }

}