Change UITableView section header when it's on top - swift

Question

I am using a custom header from Xib file for my table view using this code:
func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
let result: Result = (self.responseData?.result![section])!
let headerCell = Bundle.main.loadNibNamed("HeaderViewTableViewCell", owner: self, options: nil)?.first as! HeaderViewTableViewCell
headerCell.sectionName.text = "Title"
if (section == 0) {
headerCell.sectionName.textColor = UIColor(red: 49/255.0, green: 149/255.0, blue: 213/255.0, alpha: 1)
}
return headerCell
}
Then I want to change the header sectionName when it is scrolled to top, I have tried this code
let topSection = self.mainTable .indexPathsForVisibleRows?.first?.section
let currentHeader : HeaderViewTableViewCell = self.mainTable .headerView(forSection: topSection!) as HeaderViewTableViewCell
currentHeader.sectionName.textColor = UIColor.red
But I get this error: Cannot convert value of type 'UITableViewHeaderFooterView?' to type 'HeaderViewTableViewCell' in coercion
Is there any way to cast the headerView to my custom type?

Answer 1

First of all I suggest you to use UITableViewHeaderFooterView for your header view. You can make a subclass and add custom code. For this example I will use an empty subclass:
class HeaderView: UITableViewHeaderFooterView {
override func prepareForReuse() {
super.prepareForReuse()
// set you default color (other properties) here.
// when scrolling fast the view gets reused and sometimes
// the view that's on top will suddenly appear on the bottom still with the previous values
textLabel?.textColor = .black
}
}
Register your header view (I am skipping all other unrelated code):
override func viewDidLoad() {
super.viewDidLoad()
tableView.register(HeaderView.self, forHeaderFooterViewReuseIdentifier: "Header")
// If you have a nib file for your HeaderView then register nib instead
// Make sure in our nib file you set class name to HeaderView
// And the file name is also HeaderView.xib
// tableView.register(UINib.init(nibName: "HeaderView", bundle: nil) , forHeaderFooterViewReuseIdentifier: "Header")
}
Implement delegate methods:
func tableView(_ tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {
return 44
}
func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
let view = tableView.dequeueReusableHeaderFooterView(withIdentifier: "Header")
view?.textLabel?.text = "Hello"
return view
}
Create a method for updating headers:
// Iterates through section header views and
// checks for positions in relation to the tableview offset
func updateHeaders() {
var sectionHeaders: [Int: HeaderView?] = [:]
var i = 0
while i < numberOfSections {
sectionHeaders[i] = tableView.headerView(forSection: i) as? HeaderView
i += 1
}
let availableHeaders = sectionHeaders.flatMap { $0.value != nil ? $0 : nil }
for (index, header) in availableHeaders {
let rect = tableView.rectForHeader(inSection: index)
if rect.origin.y <= tableView.contentOffset.y + tableView.contentInset.top || index == 0 {
header!.textLabel?.textColor = .red
} else {
header!.textLabel?.textColor = .black
}
}
}
And call your updateHeaders() from UIScrollViewDelegate method scrollViewDidScroll:
func scrollViewDidScroll(_ scrollView: UIScrollView) {
updateHeaders()
}
Also update headers before the view will be displayed (before any scroll appeared), for that use the UITableViewDelegate method willDisplayHeaderView:
func tableView(_ tableView: UITableView, willDisplayHeaderView view: UIView, forSection section: Int) {
updateHeaders()
}