您要做的是，如果生成的行高小于表视图框架的高度，则设置表视图的.contentInset.bottom。
我们将从一个简单的动态高度单元格（多行标签）开始：

class DynamicHeightCell: UITableViewCell {
    
    let theLabel: UILabel = {
        let v = UILabel()
        v.numberOfLines = 0
        v.backgroundColor = UIColor(white: 0.95, alpha: 1.0)
        return v
    }()
    
    override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {
        super.init(style: style, reuseIdentifier: reuseIdentifier)
        commonInit()
    }
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }
    
    func commonInit() {
        theLabel.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(theLabel)
        let g = contentView.layoutMarginsGuide
        NSLayoutConstraint.activate([
            theLabel.topAnchor.constraint(equalTo: g.topAnchor),
            theLabel.leadingAnchor.constraint(equalTo: g.leadingAnchor),
            theLabel.trailingAnchor.constraint(equalTo: g.trailingAnchor),
            theLabel.bottomAnchor.constraint(equalTo: g.bottomAnchor),
        ])
    }
}

以及具有表格视图的基本控制器，从每侧插入40个点：

class TableInsetVC: UIViewController, UITableViewDelegate, UITableViewDataSource {
    
    // set the number of rows to use
    //  once we get past 7 (or so), the rows will be
    //  taller than the tableView frame
    let testRowCount = 5
    
    let tableView: UITableView = {
        let v = UITableView()
        return v
    }()
    
    // we'll cycle through colors for the cell backgrounds
    //  to make it easier to see the cell frames
    let bkgColors: [UIColor] = [
        .systemRed, .systemGreen, .systemBlue, .systemYellow, .systemCyan, .systemBrown,
    ]
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = .systemBackground
        
        [tableView].forEach { v in
            v.translatesAutoresizingMaskIntoConstraints = false
            view.addSubview(v)
        }
        
        let g = view.safeAreaLayoutGuide
        
        NSLayoutConstraint.activate([
            
            tableView.topAnchor.constraint(equalTo: g.topAnchor, constant: 40.0),
            tableView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 40.0),
            tableView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -40.0),
            tableView.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: -40.0),
            
        ])
        
        tableView.register(DynamicHeightCell.self, forCellReuseIdentifier: "c")
        tableView.dataSource = self
        tableView.delegate = self
        
        // so we can see the tableView frame
        tableView.backgroundColor = .lightGray
        
        tableView.contentInset.top = 150
        tableView.contentOffset.y = -150
        
    }
    
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return testRowCount
    }
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let c = tableView.dequeueReusableCell(withIdentifier: "c", for: indexPath) as! DynamicHeightCell
        
        // we want dynamic height cells, so
        var s = "Row: \(indexPath.row + 1)"
        
        // to make it easy to see it's the last row
        if indexPath.row == tableView.numberOfRows(inSection: 0) - 1 {
            s += " --- Last Row"
        }
        
        // fill cells with 1 to 4 rows of text
        for i in 0..<(indexPath.row % 4) {
            s += "\nThis is Line \(i + 2)"
        }

        c.theLabel.text = s

        // cycle background color to make it easy to see the cell frames
        c.contentView.backgroundColor = bkgColors[indexPath.row % bkgColors.count]
        
        return c
    }
    
}

运行时如下所示：

不过，到目前为止，它处于您当前的状态--我们无法向上滚动到顶部。
我们需要做的是找到一种方法来设置表视图的.contentInset.bottom：

因此，我们将实现scrollViewDidScroll(...)：

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    
    // unwrap optional
    if let rows = tableView.indexPathsForVisibleRows {
        
        // get indexPath of final cell
        let n = tableView.numberOfRows(inSection: 0)
        let lastRowIndexPath = IndexPath(row: n - 1, section: 0)
        
        // if final cell is visible
        if rows.contains(lastRowIndexPath) {
            
            // we now know the tableView's contentSize, so
            //  if .contentSize.height is less than tableView.frame.height
            if tableView.contentSize.height < tableView.frame.height {
                // calculate and set bottom inset
                tableView.contentInset.bottom = tableView.frame.height - tableView.contentSize.height
            }
            
        }
        
    }
    
}

现在，当我们运行它时，我们可以“滚动到顶部”：

将控制器顶部的testRowCount从5更改为6、7、8、20、30等。一旦有足够的行（或行更高），表格视图就可以滚动到顶部，* 无需 * .contentInset.bottom，我们就可以在保持150点顶部插图的同时进行“正常”滚动。
值得注意的是：上面的scrollViewDidScroll代码将在每次滚动表格时运行。理想情况下，我们只会让它运行，直到我们确定了底部偏移量（如果需要的话）。
为此，我们需要一些新的var属性和一些if测试。
下面是另一个版本的控制器，一旦我们知道需要什么，它就会停止测试：

class TableInsetVC: UIViewController, UITableViewDelegate, UITableViewDataSource {

    // we'll use this for both the .contentInset.bottom
    //  AND to stop testing the height when we've determined whether it's needed or not
    var bottomInset: CGFloat = -1

    // we don't want to start testing the height until AFTER initial layout has finished
    //  so we'll use this as a flag
    var hasAppeared: Bool = false

    // set the number of rows to use
    //  once we get past 7 (or so), the rows will be
    //  taller than the tableView frame
    let testRowCount = 5

    let tableView: UITableView = {
        let v = UITableView()
        return v
    }()
    
    // we'll cycle through colors for the cell backgrounds
    //  to make it easier to see the cell frames
    let bkgColors: [UIColor] = [
        .systemRed, .systemGreen, .systemBlue, .systemYellow, .systemCyan, .systemBrown,
    ]
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = .systemBackground
        
        [tableView].forEach { v in
            v.translatesAutoresizingMaskIntoConstraints = false
            view.addSubview(v)
        }
        
        let g = view.safeAreaLayoutGuide
        
        NSLayoutConstraint.activate([
            
            tableView.topAnchor.constraint(equalTo: g.topAnchor, constant: 40.0),
            tableView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 40.0),
            tableView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -40.0),
            tableView.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: -40.0),
            
        ])
        
        tableView.register(DynamicHeightCell.self, forCellReuseIdentifier: "c")
        tableView.dataSource = self
        tableView.delegate = self
        
        // so we can see the tableView frame
        tableView.backgroundColor = .lightGray
        
        tableView.contentInset.top = 150
        tableView.contentOffset.y = -150
        
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        hasAppeared = true
    }
    
    func scrollViewDidScroll(_ scrollView: UIScrollView) {

        // initial layout has finished, AND we have not yet changed bottomInset
        if hasAppeared, bottomInset == -1 {

            // unwrap optional
            if let rows = tableView.indexPathsForVisibleRows {

                // get indexPath of final cell
                let n = tableView.numberOfRows(inSection: 0)
                let lastRowIndexPath = IndexPath(row: n - 1, section: 0)
                
                // if final cell is visible
                if rows.contains(lastRowIndexPath) {

                    // we now know the tableView's contentSize, so
                    //  if .contentSize.height is less than tableView.frame.height
                    if tableView.contentSize.height < tableView.frame.height {
                        // calculate and set bottom inset
                        bottomInset = tableView.frame.height - tableView.contentSize.height
                        tableView.contentInset.bottom = bottomInset
                    } else {
                        // .contentSize.height is greater than tableView.frame.height
                        //  so we don't set .contentInset.bottom
                        //  and we set bottomInset to -2 so we stop testing
                        bottomInset = -2
                    }
                    
                } else {
                    
                    // final cell is not visible, so
                    // if we have scrolled up past the top,
                    //  we know the full table is taller than the tableView
                    //  and we set bottomInset to -2 so we stop testing
                    if tableView.contentOffset.y >= 0 {
                        bottomInset = -2
                    }
                    
                }
            }
            
        }

    }
    
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return testRowCount
    }
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let c = tableView.dequeueReusableCell(withIdentifier: "c", for: indexPath) as! DynamicHeightCell
        
        // we want dynamic height cells, so
        var s = "Row: \(indexPath.row + 1)"
        
        // to make it easy to see it's the last row
        if indexPath.row == tableView.numberOfRows(inSection: 0) - 1 {
            s += " --- Last Row"
        }
        
        // fill cells with 1 to 4 rows of text
        for i in 0..<(indexPath.row % 4) {
            s += "\nThis is Line \(i + 2)"
        }
        
        c.theLabel.text = s
        
        // cycle background color to make it easy to see the cell frames
        c.contentView.backgroundColor = bkgColors[indexPath.row % bkgColors.count]

        return c
    }
    
}