UITableView

UITableView-specific things.

DiffableDataSource

New in iOS 13 is UITableViewDiffableDataSource. A generic class which does the heavy lifting of determining updates for a tableview. This class allows you to make edits to the tableView in a much more type-safe way. ALl that it requires is that your sections and row models be Hashable.

You initialize it by passing in a tableView and a way to create the tableView cells. Updates come in the form of “snapshots”. The simplest way is to just give it a snapshot of the entirely new data and let the class figure out what the diff is. It’s pretty cool.

Section Titles

Section titles are asserted by checking the headerView(forSection:). You can then check the textLabel.text properties to get the displayed text. Note that this needs the section header to be within the view in order to be non-nil. Otherwise you need to scroll to show that.

Actually setting this is done by implementing the tableView(_:titleForHeaderInSection:) method on the dataSource.

Table Header/Footer Views

The docs for tableHeaderView state that the width will be maintained by the tableview, but you set the height. Don’t set this view up for autolayout, as you’ll get weird width issues (translatesAutoresizingMaskIntoConstraints should be true, not false).

Sizing a tableview with autolayout is non-obvious, adding this snippet does the trick, do it every time the view lays out/will change size.

tableView.tableHeaderView.frame.size.height = tableView.tableHeaderView.systemLayoutSizeFitting(
    UIView.layoutFittingCompressedSize
).height

Scrolling under test

In order to scroll to a row, you invoke the scrollToRow(at:at:animated:) method. You also need the view to be within a visible window. This is also animated, so you’ll to wait a bit before you do the next assertion.

let window = UIWindow(frame: CGRect(x: 0, y: 0, width: 320, height: 480))
window.rootViewController = subject
window.makeKeyAndVisible()

let indexPath = IndexPath(row: 3, section: 1)

subject.tableView.scrollToRow(at: indexPath, at: .middle, animated: false)

expect(subject.tableView.indexPathsForVisibleRows).toEventually(contain(indexPath))

Context Menus

In iOS 13, we get context menus. These replaced the previous “listen to 3d touch events on the entire table view, and from there figure out which cell was pressed” stuff we had to do before (or at least, had to do in iOS 9 - when I last implemented that behavior).

The minimum delegate methods required to implement this behavior are:

• -tableView(:contextMenuConfigurationForRowAt:point:)
• -tableView(:willPerformPreviewActionForMenuWith:animator:

-tableView(:contextMenuConfigurationForRowAt:point:) is used to set up the menu for that item (what happens when you long/force press on the tableView). It returns an optional UIContextMenuConfiguration, which is used to set up the view controller to show, and a UIMenu to show with it.

-tableView(:willPerformPreviewActionForMenuWith:animator: is then used to commit that.

For example, see this example from my rss reader:

extension ArticleListController: UITableViewDelegate {
    // ...
    public func tableView(_ tableView: UITableView, contextMenuConfigurationForRowAt indexPath: IndexPath,
                          point: CGPoint) -> UIContextMenuConfiguration? {
        guard ArticleListSection(rawValue: indexPath.section) == .articles else { return nil }

        let article = self.articleForIndexPath(indexPath)
        return UIContextMenuConfiguration(
            identifier: article.link as NSURL,
            previewProvider: { return self.articleViewController(article) },
            actionProvider: { elements in
                return UIMenu(title: article.title, image: nil, identifier: nil, options: [],
                              children: elements + self.menuActions(for: article))
        })
    }

    public func tableView(_ tableView: UITableView,
                          willPerformPreviewActionForMenuWith configuration: UIContextMenuConfiguration,
                          animator: UIContextMenuInteractionCommitAnimating) {
        guard let articleController = animator.previewViewController as? ArticleViewController else { return }
        animator.addCompletion {
            self.markRead(article: articleController.article, read: true)
            self.showArticleController(articleController, animated: true)
        }
    }
}

Last updated: 2020-06-07 16:24:37 -0700