Add buttons to UIScrollView Swift 5 programmatically

Question

I'm trying to add a number of buttons programmatically in a grid, where the number of rows exceeds the screen size, so I want them in a UIScrollView.

My minimal working example is the following:

class ViewController: UIViewController {
    
    //center label and down a bit
    let label = UILabel(frame: CGRect(x: UIScreen.main.bounds.width/2 - 100, y: 50, width: 200, height: 200))
    
    // start scroll view underneath label (why not y: 250?)
    let scrollView = UIScrollView(frame: CGRect(x: 0, y: 50, width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height))
    
    override func viewDidLoad() {
        super.viewDidLoad()
                
        // add label to view
        self.view.addSubview(label)
        
        // add Scrollview
        self.view.addSubview(scrollView)
        // uncommenting the following also doesn't work
        //scrollView.contentSize = CGSize(width: UIScreen.main.bounds.width, height: 4000)
        
        // add buttons to scroll view in 5x21 grid
        var idx = 1
        for row in 0...20 {
            for col in 0...4 {
                let button = UIButton(frame: CGRect(x: col*50, y: row*50 + 200, width: 50, height: 50))
                button.backgroundColor = .gray
                button.setTitle("\(idx)", for: .normal)
                button.addTarget(self, action: #selector(buttonAction), for: .touchUpInside)
                
                // add button to scroll view
                scrollView.addSubview(button)
                
                idx += 1
            }
        }
    }
    
    @objc func buttonAction(sender: UIButton!) {
        label.text = sender.title(for: .normal)
    }

}

Unfortunately the scrolling doesn't work. Even when I explicitly set a larger vertical content size (see commented line) //scrollView.contentSize

I'm wondering if it has something to do with setting x and y values for the buttons fixed? But then how else would I align them in a grid?

So, how do I get the button alignment I want while getting a working ScrollView?

Answer 1

You really should be using Auto-Layout!!!

By far, the easiest way to add buttons (or any view) to a scroll view - in a grid layout like you're asking - and have it automatically determine the scrolling area is with stack views.

Here's a quick example:

class ViewController: UIViewController {
    
    let label = UILabel()
    let scrollView = UIScrollView()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // start with some text in the label
        label.text = "Tap a button"
        
        // center the text in the label
        label.textAlignment = .center
        
        // so we can see the frames
        label.backgroundColor = .yellow
        scrollView.backgroundColor = UIColor(white: 0.9, alpha: 1.0)
        
        // create a vertical stack view to hold the rows of buttons
        let verticalStackView = UIStackView()
        verticalStackView.axis = .vertical

        // we're going to use auto-layout
        label.translatesAutoresizingMaskIntoConstraints = false
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        verticalStackView.translatesAutoresizingMaskIntoConstraints = false

        // add label to view
        self.view.addSubview(label)
        
        // add Scrollview to view
        self.view.addSubview(scrollView)
        
        // add stack view to scrollView
        scrollView.addSubview(verticalStackView)

        // now let's create the buttons and add them
        var idx = 1
        
        for row in 0...20 {
            // create a "row" stack view
            let rowStack = UIStackView()
            // add it to the vertical stack view
            verticalStackView.addArrangedSubview(rowStack)
            
            for col in 0...4 {
                let button = UIButton()
                button.backgroundColor = .gray
                button.setTitle("\(idx)", for: .normal)
                button.addTarget(self, action: #selector(buttonAction), for: .touchUpInside)
                
                // add button to row stack view
                rowStack.addArrangedSubview(button)
                
                // buttons should be 50x50
                NSLayoutConstraint.activate([
                    button.widthAnchor.constraint(equalToConstant: 50.0),
                    button.heightAnchor.constraint(equalToConstant: 50.0),
                ])
                
                idx += 1
            }
        }

        // finally, let's set our constraints
        
        // respect safe-area
        let safeG = view.safeAreaLayoutGuide

        NSLayoutConstraint.activate([
            
            // constrain label
            //  50-pts from top
            //  80% of the width
            //  centered horizontally
            label.topAnchor.constraint(equalTo: safeG.topAnchor, constant: 50.0),
            label.widthAnchor.constraint(equalTo: safeG.widthAnchor, multiplier: 0.8),
            label.centerXAnchor.constraint(equalTo: safeG.centerXAnchor),
            
            // constrain scrollView
            //  50-pts from bottom of label
            //  Leading and Trailing to safe-area with 8-pts "padding"
            //  Bottom to safe-area with 8-pts "padding"
            scrollView.topAnchor.constraint(equalTo: label.bottomAnchor, constant: 50.0),
            scrollView.leadingAnchor.constraint(equalTo: safeG.leadingAnchor, constant: 8.0),
            scrollView.trailingAnchor.constraint(equalTo: safeG.trailingAnchor, constant: -8.0),
            scrollView.bottomAnchor.constraint(equalTo: safeG.bottomAnchor, constant: -8.0),
            
            // constrain vertical stack view to scrollView Content Layout Guide
            //  8-pts all around (so we have a little "padding")
            verticalStackView.topAnchor.constraint(equalTo: scrollView.contentLayoutGuide.topAnchor, constant: 8.0),
            verticalStackView.leadingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.leadingAnchor, constant: 8.0),
            verticalStackView.trailingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.trailingAnchor, constant: -8.0),
            verticalStackView.bottomAnchor.constraint(equalTo: scrollView.contentLayoutGuide.bottomAnchor, constant: -8.0),
            
        ])

    }
    
    @objc func buttonAction(sender: UIButton!) {
        label.text = sender.title(for: .normal)
    }
    
}

and this is the result:

then we'll scroll down and tap a different button:

If you want spacing between the buttons, you can add something like this at the end of viewDidLoad():

// suppose we want 8-pts spacing between the buttons?
verticalStackView.spacing = 8.0
verticalStackView.arrangedSubviews.forEach { v in
    if let stack = v as? UIStackView {
        stack.spacing = 8.0
    }
}

Now it looks like this:

If you want the grid of buttons centered horizontally, or if you want the spacing (or button sizes) to adjust to fit, there are a few different ways to do that... You didn't describe your ultimate goal in your question, but this should be a good starting point.

Answer 2

I did the same thing with a collection view which is a subclass of scrollview and that would fit your need in terms of rows/columns.

In addition, to manage touches for a scrollview you have to implement a UIScrollViewDelegate for the scrollview, in particular to distinguish between touching and scrolling otherwise you will possibly end up with unpredictable behaviour.