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title author category excerpt status
UITableViewHeaderFooterView
Mattt
Cocoa
Sure, everyone knows that they can (and should!) reuse table view cells. But did you know that you can do the same for section headers and footers?
swift
5.0

UITableView is the bread and butter of iOS apps. This is as true today as it was with the first iPhone over a decade ago.

Back in those early days, developers worked hard to achieve smooth scroll performance --- often resorting to extreme measures. For example, to achieve 60FPS on a table view with custom cells on an iPhone 3G you'd often have to draw text directly to a cell's Core Graphics context, because compositing subviews was too slow. (Interface Builder? Auto Layout? Phooey! Back in my day, we calculated all of our view frames by hand --- up hill, both ways, in the snow)

At the time, the highest praise a developer could receive for their efforts was to have someone describe theirs as "buttery": smooth, responsive, without any jitter. And we milked that hardware for all it was worth to make that happen.

In honor of all the skeuomorphic sweat spilled to transmute code into that most golden of dairy products, and in the interest of maximizing the performance of our apps today, we'll turn our attention to a class that --- for many of us --- has been hiding in plain sight: UITableViewHeaderFooterView.


Introduced in iOS 6, UITableViewHeaderFooterView takes the reuse functionality of table view cells and makes it available to section headers and footers. You can either use it directly or create a subclass to customize its appearance.

Now, table views are responsible for a great deal of functionality, and one can easily lose track of how all of its responsibilities are delegated. So let's start with a quick run-down of UITableView before going into more detail about UITableViewHeaderFooterView:

UITableView Review

A UITableView consists of sections, each of which containing a number of rows.

For each row, the table view's dataSource is responsible for returning a UITableViewCell to represent each section / row index path with the tableView(_:cellForRowAt:) delegate method. The table view's dataSource may also provide a title to be displayed in the header or footer of a section by implementing the optional tableView(_:titleForHeaderInSection:) and tableView(_:titleForFooterInSection:) delegate methods.

To customize the appearance of section headers or footers, the table view's delegate can implement the optional delegate methods tableView(_:viewForHeaderInSection:) and tableView(_:viewForFooterInSection:). To keep scroll performance snappy, table views recycle their cells as they scroll out of view. This process is known as cell reuse. You can take advantage of reuse for section headers and footers, by returning an instance of UITableViewHeaderFooterView (or a subclass).

{% info %} Perhaps the main reason why so few developers know about UITableViewHeaderFooterView is that even after its introduction in iOS 6, tableView(_:viewForHeaderInSection:) and tableView(_:viewForFooterInSection:) continue to return an optional UIView. Why? It's all to do with the iOS platform team's commitment to API compatibility. An app written against the iPhone OS 2 SDK should (theoretically) still build and run on iOS 12! {% endinfo %}


What better way to demonstrate this obscure technique for buttery performance than to create an app to display per-capita dairy product consumption statistics from the USDA? (That was a hypothetical question.)

{% asset uitableviewheaderfooterview-storyboard.png %}


For our example, we'll keep our model nice and simple, with a nearly 1:1 mapping with the API we'll use to display this information on a table view:

struct Section {
    let title: String
    let image: UIImage
    let rows: [(year: Int, amount: Decimal)]
    let notes: String?
}

let butter = Section(title: "Butter",
                     image: #imageLiteral(resourceName: "Butter"),
                     rows: [ <#...#> ],
                     notes: nil)

// etc.

let sections: [Section] = [
    milk, yogurt, butter, cheese,
    cottageCheese, condensedMilk, iceCream, whey
]

In the view controller itself, the implementation for UITableViewDataSource delegate methods is cool and refreshing:

import UIKit

final class ViewController: UIViewController {
    @IBOutlet var tableView: UITableView!
}

// MARK: - UITableViewDataSource

extension ViewController: UITableViewDataSource {
    func numberOfSections(in tableView: UITableView) -> Int {
        return sections.count
    }

    func tableView(_ tableView: UITableView,
                   numberOfRowsInSection section: Int) -> Int {
        return sections[section].rows.count
    }

    func tableView(_ tableView: UITableView,
                   cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "Cell",
                                                 for: indexPath)

        let section = sections[indexPath.section]
        let row = section.rows[indexPath.row]

        cell.textLabel?.text = "\(row.year)"
        cell.detailTextLabel?.text = "\(row.amount)"

        return cell
    }
}

Alright, let's cut the cheese and talk about the right wheyway to use UITableViewHeaderFooterView.

Creating a Section Header View

In this example, we'll offer two different approaches to working with UITableViewHeaderFooterView.

In the first, we'll do everything in code; in the second, we'll design things visually in Interface Builder. Feel free to adopt whichever one you prefer.

Option 1: Constructing the View Programmatically

Similar to UITableViewCell each UITableViewHeaderFooterView comes with textLabel and detailTextLabel properties that are lazily created and positioned within a contentView. As with cells, you have the option to take or leave these built-in subviews for your custom subclass.

For our example, let's use the existing textLabel and add an imageView along the trailing margin of the contentView. We do all of this in the designated initializer, init(reuseIdentifier:):

import UIKit

final class SectionHeaderView: UITableViewHeaderFooterView {
    static let reuseIdentifier: String = String(describing: self)

    var imageView: UIImageView

    override init(reuseIdentifier: String?) {
        super.init(reuseIdentifier: reuseIdentifier)

        imageView = UIImageView()
        contentView.addSubview(imageView)

        imageView.translatesAutoresizingMaskIntoConstraints = false

        imageView.widthAnchor.constraint(equalToConstant: 24.0).isActive = true
        imageView.heightAnchor.constraint(equalToConstant: 24.0).isActive = true
        imageView.trailingAnchor.constraint(equalTo: contentView.layoutMarginsGuide.trailingAnchor).isActive = true
        imageView.bottomAnchor.constraint(equalTo: contentView.layoutMarginsGuide.bottomAnchor).isActive = true
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
}

In our view controller, we register the custom section header in viewDidLoad() by calling the register(_:forHeaderFooterViewReuseIdentifier:) method on tableView:

import UIKit

final class ViewController: UIViewController {
    @IBOutlet var tableView: UITableView!

    // MARK: UIViewController

    override func viewDidLoad() {
        super.viewDidLoad()

        self.tableView.register(
            SectionHeaderView.self,
            forHeaderFooterViewReuseIdentifier:
                SectionHeaderView.reuseIdentifier
        )
    }
}

Option 2: Designing the View in Interface Builder

Dynamic table view cells can be designed directly from a Storyboard, which can be quite convenient for prototyping interfaces. Unfortunately, at the time of writing, there is no documented way to design prototype section header / footer views as you can with table view cells.

However, we can still use Interface Builder to design our section header and footer views --- all it takes a few extra steps.

First, create a new Swift file that declares your UITableViewHeaderFooterView subclass.

Next, create a new XIB file for your custom view:

{% asset uitableviewheaderfooterview-new-xib.png %}

In Interface Builder, navigate to the Identity Inspector in the Inspectors panel on the right-hand side, and set your subclass as the "Custom Class" for both File's Owner and the top-level view.

{% asset uitableviewheaderfooterview-custom-view.png %}

Back in your subclass implementation, declare an imageView property and an override to the existing textLabel property --- both with @IBOutlet annotations --- and connect them to their counterparts in Interface Builder.

import UIKit

final class SectionHeaderView: UITableViewHeaderFooterView {
    static let reuseIdentifier: String = String(describing: self)

    static var nib: UINib {
        return UINib(nibName: String(describing: self), bundle: nil)
    }

    // Override `textLabel` to add `@IBOutlet` annotation
    @IBOutlet override var textLabel: UILabel? {
        get { return _textLabel }
        set { _textLabel = newValue }
    }
    private var _textLabel: UILabel?

    @IBOutlet var imageView: UIImageView!
}

{% warning %} This step isn't required for using UITableViewHeaderFooterView with Interface Builder. As an alternative to overriding textLabel, you can declare a new label property to use instead. {% endwarning %}

Now, when you register your subclass for reuse with the table view controller, pass a UINib (provided here in a type property) instead of SectionHeaderView.self.

import UIKit

final class ViewController: UIViewController {
    @IBOutlet var tableView: UITableView!

    // MARK: UIViewController

    override func viewDidLoad() {
        super.viewDidLoad()

        self.tableView.register(
            SectionHeaderView.nib,
            forHeaderFooterViewReuseIdentifier:
                SectionHeaderView.reuseIdentifier
        )
    }
}

Implementing UITableViewDelegate Methods

From here, it's smooth scrolling sailing. Enjoy your victory lap as you implement the requisite UITableViewDelegate methods:

import UIKit

// MARK: - UITableViewDelegate

extension ViewController: UITableViewDelegate {
    func tableView(_ tableView: UITableView,
                   titleForHeaderInSection section: Int) -> String? {
        return sections[section].title
    }

    func tableView(_ tableView: UITableView,
                   titleForFooterInSection section: Int) -> String? {
        return sections[section].notes
    }

    func tableView(_ tableView: UITableView,
                   viewForHeaderInSection section: Int) -> UIView? {
        guard let view = tableView.dequeueReusableHeaderFooterView(
                            withIdentifier: SectionHeaderView.reuseIdentifier)
                            as? SectionHeaderView
        else {
            return nil
        }

        view.textLabel?.text = sections[section].title
        view.imageView?.image = sections[section].image

        return view
    }
}

With today's comparatively over-powered iOS hardware, such proactive measures may well be unnecessary for achieving buttery smooth interactions.

But for those of your with demanding performance requirements, for anyone yearning to be in the 2%, to achieve the crème de la crème of responsive interfaces, UITableViewHeaderFooterView can be a great way to skim some fat off your code.

If nothing else, its restrained, familiar API allows UITableViewHeaderFooterView to be added to most codebases without introducing much churn.

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