1import UIKit
2
3class ViewController: UIViewController {
4    override func viewDidLoad() {
5        super.viewDidLoad()
6
7        let label = UILabel()
8        label.text = "Hello, World!"
9        label.textAlignment = .center
10        label.translatesAutoresizingMaskIntoConstraints = false
11
12        view.addSubview(label)
13
14        NSLayoutConstraint.activate([
15            label.centerXAnchor.constraint(equalTo: view.centerXAnchor),
16            label.centerYAnchor.constraint(equalTo: view.centerYAnchor)
17        ])
18    }
19}

1// Center horizontally but position vertically at 1/3 from top
2NSLayoutConstraint.activate([
3    label.centerXAnchor.constraint(equalTo: view.centerXAnchor),
4    label.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 100)
5])
6
7// Center within a container view (not the full screen)
8let container = UIView()
9container.translatesAutoresizingMaskIntoConstraints = false
10view.addSubview(container)
11
12// Set up container constraints first
13NSLayoutConstraint.activate([
14    container.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
15    container.leadingAnchor.constraint(equalTo: view.leadingAnchor),
16    container.trailingAnchor.constraint(equalTo: view.trailingAnchor),
17    container.heightAnchor.constraint(equalToConstant: 200)
18])
19
20// Then center label within the container
21container.addSubview(label)
22NSLayoutConstraint.activate([
23    label.centerXAnchor.constraint(equalTo: container.centerXAnchor),
24    label.centerYAnchor.constraint(equalTo: container.centerYAnchor)
25])

1// textAlignment centers the TEXT within the label's frame
2label.textAlignment = .center
3
4// For a label with a fixed width, this matters:
5NSLayoutConstraint.activate([
6    label.centerXAnchor.constraint(equalTo: view.centerXAnchor),
7    label.centerYAnchor.constraint(equalTo: view.centerYAnchor),
8    label.widthAnchor.constraint(equalToConstant: 300)  // Fixed width
9])
10// textAlignment = .center ensures text is centered within the 300pt width
11
12// For multi-line labels
13label.numberOfLines = 0  // Unlimited lines
14label.textAlignment = .center
15label.lineBreakMode = .byWordWrapping
16
17NSLayoutConstraint.activate([
18    label.centerXAnchor.constraint(equalTo: view.centerXAnchor),
19    label.centerYAnchor.constraint(equalTo: view.centerYAnchor),
20    label.leadingAnchor.constraint(greaterThanOrEqualTo: view.leadingAnchor, constant: 20),
21    label.trailingAnchor.constraint(lessThanOrEqualTo: view.trailingAnchor, constant: -20)
22])

1// In Interface Builder:
2// 1. Drag a UILabel onto the view
3// 2. Select the label
4// 3. Click the "Align" button (bottom of canvas)
5// 4. Check "Horizontally in Container" and "Vertically in Container"
6// 5. Click "Add 2 Constraints"
7
8// Or use Control-drag:
9// 1. Control-drag from label to the superview
10// 2. Select "Center Horizontally in Safe Area"
11// 3. Control-drag again, select "Center Vertically in Safe Area"
12
13// Via the Size Inspector, verify:
14// - Align Center X to: Safe Area
15// - Align Center Y to: Safe Area

1let stackView = UIStackView()
2stackView.axis = .vertical
3stackView.alignment = .center       // Centers children horizontally
4stackView.distribution = .fill
5stackView.translatesAutoresizingMaskIntoConstraints = false
6
7let label = UILabel()
8label.text = "Centered via StackView"
9stackView.addArrangedSubview(label)
10
11view.addSubview(stackView)
12
13NSLayoutConstraint.activate([
14    stackView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
15    stackView.centerYAnchor.constraint(equalTo: view.centerYAnchor)
16])

1import SwiftUI
2
3// Views are centered by default in SwiftUI
4struct ContentView: View {
5    var body: some View {
6        Text("Hello, World!")
7            // Already centered in the available space
8    }
9}
10
11// Explicit centering with frame
12struct ExplicitCenterView: View {
13    var body: some View {
14        Text("Centered")
15            .frame(maxWidth: .infinity, maxHeight: .infinity)
16            .background(Color.gray.opacity(0.2))
17    }
18}
19
20// Center within a specific area
21struct PartialCenterView: View {
22    var body: some View {
23        VStack {
24            Text("Centered in top half")
25                .frame(maxWidth: .infinity, maxHeight: .infinity)
26            Spacer()
27        }
28        .frame(height: 300)
29    }
30}