问UITableView tableFooterView显示在UITableView顶部-错误

EN

   @IBOutlet weak var tableView: UITableView!

override func viewDidLoad() {
    super.viewDidLoad()

    tableView.delegate = self
    tableView.dataSource = self

    let footerView = UIView(frame: CGRect.init(x: 0, y: 0, width: tableView.frame.width, height: 50))
    footerView.backgroundColor = UIColor.green
    tableView.tableFooterView = footerView
}

extension ViewController: UITableViewDelegate, UITableViewDataSource {

func numberOfSections(in tableView: UITableView) -> Int {
    return 1
}

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return 10
}

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "cell")
    cell?.textLabel?.text = "\(indexPath.row)"
    return cell!
}

//
// this assumes IBOutlet has been set for "theTableView"
//

- (void)viewDidLoad {
    [super viewDidLoad];

    // standard stuff
    [_theTableView registerClass:[UITableViewCell class] forCellReuseIdentifier:@"simpleCell"];
    _theTableView.delegate = self;
    _theTableView.dataSource = self;

    // instantiate a view for the table footer
    // width doesn't matter (it will be stretched to fit the table by default)
    // set height to a big number to avoid a "will attempt to break constraint" warning
    UIView *footerContainer = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 1, 1000)];

    // give it a color so we can see it
    footerContainer.backgroundColor=[UIColor greenColor];

    // set the footer view
    _theTableView.tableFooterView = footerContainer;


    // instantiate a label to add to the footer view
    UILabel *aLabel = [UILabel new];

    // auto-sizing the height, so set lines to zero
    aLabel.numberOfLines = 0;

    // give it a color so we can see it
    aLabel.backgroundColor = [UIColor yellowColor];

    // set the text to 8 lines for demonstration purposes
    aLabel.text = @"Line 1\nLine 2\nLine 3\nLine 4\nLine 5\nLine 6\nLine 7\nLine 8";

    // standard, for auto-sizing
    aLabel.translatesAutoresizingMaskIntoConstraints = NO;

    // add the label to the footer view
    [footerContainer addSubview:aLabel];

    // constraint the label to 8-pts from each edge...
    [aLabel.topAnchor constraintEqualToAnchor:footerContainer.topAnchor constant:8.0].active = YES;
    [aLabel.leftAnchor constraintEqualToAnchor:footerContainer.leftAnchor constant:8.0].active = YES;
    [aLabel.rightAnchor constraintEqualToAnchor:footerContainer.rightAnchor constant:-8.0].active = YES;
    [aLabel.bottomAnchor constraintEqualToAnchor:footerContainer.bottomAnchor constant:-8.0].active = YES;

}

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];

    // get a reference to the table's footer view
    UIView *currentFooterView = [_theTableView tableFooterView];

    // if it's a valid reference (the table *does* have a footer view)
    if (currentFooterView) {

        // tell auto-layout to calculate the size based on the footer view's content
        CGFloat newHeight = [currentFooterView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height;

        // get the current frame of the footer view
        CGRect currentFrame = currentFooterView.frame;

        // we only want to do this when necessary (otherwise we risk infinite recursion)
        // so... if the calculated height is not the same as the current height
        if (newHeight != currentFrame.size.height) {
            // use the new (calculated) height
            currentFrame.size.height = newHeight;
            currentFooterView.frame = currentFrame;
        }

    }

}