So I have the following code that creates a TableView:

    contentView.addSubview(carsTableView)
    carsTableView.translatesAutoresizingMaskIntoConstraints = false
    carsTableView.backgroundColor = r.darkGray
    carsTableView.dataSource = self
    carsTableView.isScrollEnabled = false
    carsTableView.allowsSelection = true
    carsTableView.delegate = self
    
    carsTableView.separatorStyle = UITableViewCell.SeparatorStyle.singleLine
    carsTableView.separatorColor = r.lightGray
    carsTableView.separatorInset = UIEdgeInsets(top: 0, left: 5, bottom: 0, right: 5)
    
    carsTableView.register(CarCell.self, forCellReuseIdentifier: "CarCell")

Note that I use a single line separator. The following code are constraints for my Cell "CarCell"

NSLayoutConstraint.activate([
        carView.heightAnchor.constraint(equalToConstant: 120),
        carView.topAnchor.constraint(equalTo: contentView.topAnchor),
        carView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor),
        carView.leadingAnchor.constraint(equalTo: contentView.leadingAnchor),
        carView.trailingAnchor.constraint(equalTo: contentView.trailingAnchor),
        
        carImageView.leadingAnchor.constraint(equalTo: carView.leadingAnchor, constant: 15),
        carImageView.centerYAnchor.constraint(equalTo: carView.centerYAnchor),
        carImageView.heightAnchor.constraint(equalToConstant: carImageWidthAndHeight),
        carImageView.widthAnchor.constraint(equalToConstant: carImageWidthAndHeight),
        
        carImage.widthAnchor.constraint(equalTo: carImageView.widthAnchor),
        carImage.heightAnchor.constraint(equalTo: carImageView.heightAnchor),
        carImage.centerYAnchor.constraint(equalTo: carImageView.centerYAnchor),
        carImage.centerXAnchor.constraint(equalTo: carImageView.centerXAnchor),
        
        stringStack.leadingAnchor.constraint(equalTo: carImageView.trailingAnchor, constant: 20),
        stringStack.centerYAnchor.constraint(equalTo: carView.centerYAnchor),
        
        editButton.trailingAnchor.constraint(equalTo: carView.trailingAnchor, constant: -15),
        editButton.centerYAnchor.constraint(equalTo: carView.centerYAnchor),
        
    ])

The result is a perfectly fine TableView which looks exactly like it should. However, the separator line breaks the height constraint from 120 to 120.33. How can I avoid that? I am honestly amazed by the fact that no one seems to have a similar problem. How do I get around it? The difference is obviously not noticeable, but the constraint issues bother me in the console. I'd like to have it run without throwing errors...

CodePudding user response：

This is a common issue related to the way UIKit lays out table views and cells.

You're seeing 120 to 120.3333, but if you run the app on a device with @2x screen scale, the message will be 120.5.

When calculating "single pixel" lines, @2x devices can only use whole or 1/2 points, and @3x devices can only use whole, 1/3 or 2/3 points.

It is safe to ignore, but if you want to get rid of the error / warning messages, give your cells subview(s) a bottom constraint with less-than-required priority.

For example (I'm assuming from the code you posted that carImageView, carImage, stringStack, editButton are all subviews of carView):

    let c  = carView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor)
    c.priority = .required - 1
    
    NSLayoutConstraint.activate([
        
        // don't use this one
        //carView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor),
        
        // activate the less-than-required bottom constraint
        c,
        
        // the rest of your constraints....
        carView.heightAnchor.constraint(equalToConstant: 120),
        carView.topAnchor.constraint(equalTo: contentView.topAnchor),
        carView.leadingAnchor.constraint(equalTo: contentView.leadingAnchor),
        carView.trailingAnchor.constraint(equalTo: contentView.trailingAnchor),

        // and so on....