Ggtcf

I have a UITableViewController where I want to add a UIButton in the section header.

I saw in calendar app this button, and I wanted to know if this is part of a class I can reuse, or if I need to write my own class to add it.

You need to use your own custom class for this case.
Because UITableViewHeaderFooterView does not containing any kind of buttons itself.
So, better go with your customClass.

You can create header view from storyboard and assign using identifier, See the following screenshot and code.

func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? 
 let headerView = tableView.dequeueReusableHeaderFooterView(withIdentifier: "myHeader")
 return headerView
 

Also, you can create click method directly drag and drop to your swift file like see the attached screenshot.

You have to create a xib file and create it class file.
Add your button and create its outlet.
Register your xib same in you viewDidLoad()

For example:

let headerNib = UINib(nibName: "yourNIBname", bundle: nil)
tableView.register(headerNib, forHeaderFooterViewReuseIdentifier: "reuseIdentifer")

Then add the following tableview delegate

override func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView 
 let headerView = tableView.dequeueReusableHeaderFooterView(withIdentifier: "reuseIdentifer") as! youNIBClassName
 headerView.yourButton.addTarget(self, action: #selector(hideAllTapped(withSender:)), for: .touchUpInside)
 return headerView
 

You will get the action event in your hideAllTapped() function

@objc func hideAllTapped(withSender sender: UIButton) 
 // do your action