Why does overriding tableView(:viewForHeaderInSection:) change the results - ios

Question

I have a simple implementation of a table view with no header. This is the result that I'm going for.
class NavigationController: UINavigationController {
override func viewDidLoad() {
super.viewDidLoad()
self.pushViewController(MyTable(style: .grouped), animated: false)
}
}
class MyTable: UITableViewController {
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
}
override func tableView(_ tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {
return CGFloat.leastNormalMagnitude
}
override func tableView(_ tableView: UITableView, heightForFooterInSection section: Int) -> CGFloat {
return CGFloat.leastNormalMagnitude
}
override func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 3
}
override func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
assert(false)
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
return UITableViewCell()
}
}
Notice that I have an override for viewForHeaderInSection which never gets called which is expected since the height I give is essentially zero.
override func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
assert(false)
}
When I remove the definition of the above function, then I get a different result. Why does this happen, and is there a way to get the same result without overriding this method?

Answer 1

If a UITableView's delegate implements tableView(_:viewForHeaderInSection:), the calling UITableView switches from assuming you want titles in your section headers to thinking that you want views in your section headers. Once that switch has been made, it checks the delegate's tableView(_:heightForHeaderInSection:) — and since you return (effectively) zero, I'd guess that the table view can lay out without querying the delegate for an actual view.
Keep in mind that making this switch never has to involve calling the view-for-header method. UITableView can check whether its delegate implements the ObjC selector for the method without needing to actually call it, and change its behavior accordingly. That's most likely why your assertion never fires.

Answer 2

The compiler actually throws an error if you don't have the override keyword along with the function.
Overriding declaration requires an 'override' keyword