Why do collapsing/expandable iOS UITableView rows disappear on interaction? - ios

Question

I am new to iOS Development and I just implemented a simple expandable sections UITableView. I am not able to understand why some rows disappear and sometimes change position when the row heights are recalculated on tapping the section header. I went through all the already answered questions on this topic and have not been able to find the right solution.
Following is a scenario:
Launch the app:
Tap on the section header:
Section expands
All other headers disappear
Tap again
Section collapses
The headers continue to be blank
Scrolled to the bottom and back to the top
The positions of headers changed
Scrolled to the bottom and back to the top again
The positions of headers changed again with some cells still blank
Things I have already tried:
Wrapping reloadRowsAtIndexPaths in updates block (beginUpdates() and endUpdates())
Using reloadRowsAtIndexPaths with animation set to .none
Removing reloadRowsAtIndexPaths at all while keeping the updates block
Using reloadData() instead which actually works but I lose animation
Code:
Here is the link to the project repository.

Answer 1

You're using cells for the header. You shouldn't do that, you need a regular UIView there, or at least a cell that's not being dequeued like that. There's a few warnings when you run it that give that away. Usually just make a standalone xib with the view and then have a static method like this in your header class. Make sure you tie your outlets to the view itself, and NOT the owner:
static func view() -> HeaderView {
return Bundle.main.loadNibNamed("HeaderView", owner: nil, options: nil)![0] as! HeaderView
}
You're reloading the cells in the section that grows, but when you change the section that's grown you'd need to at least reload the former section for it to take the changes to it's cell's height. You can reload the section by index instead of individual rows in both cases

Answer 2

Ok as you ask, I am changing my answer according to you.
import UIKit
class MyTableViewController: UITableViewController {
let rows = 2
var categories = [Int](repeating: 0, count: 10)
struct Constants {
static let noSelectedSection = -1
}
var selectedSection: Int = Constants.noSelectedSection
func selectedChanged(to selected: Int?) {
let oldIndex = selectedSection;
if let s = selected {
if selectedSection != s {
selectedSection = s
} else {
selectedSection = Constants.noSelectedSection
}
tableView.beginUpdates()
if(oldIndex != -1){
tableView.reloadSections([oldIndex,s], with: .automatic)
}else{
tableView.reloadSections([s], with: .automatic)
}
tableView.endUpdates()
}
}
override func numberOfSections(in tableView: UITableView) -> Int {
return categories.count
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
print("reloading section \(section)")
return (selectedSection == section) ? rows : 0;//rows
}
override func tableView(_ tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {
return tableView.rowHeight
}
override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
return tableView.rowHeight
}
override func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
let cell = tableView.dequeueReusableCell(withIdentifier: "Header")
if let categoryCell = cell as? MyTableViewCell {
categoryCell.category = section + 1
let recognizer = UITapGestureRecognizer(target: self, action: #selector(handleTapGesture))
recognizer.numberOfTapsRequired = 1
recognizer.numberOfTouchesRequired = 1
categoryCell.contentView.tag = section;
categoryCell.contentView.addGestureRecognizer(recognizer)
}
return cell?.contentView
}
func handleTapGesture(recognizer: UITapGestureRecognizer) {
if let sindex = recognizer.view?.tag {
selectedChanged(to: sindex)
}
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "Body", for: indexPath)
if let label = cell.viewWithTag(1) as? UILabel {
label.text = "Body \(indexPath.section + 1) - \(indexPath.row + 1)"
}
return cell
}
}
As you can see now I am just reloading a particular section instead of reloading the whole table.
also, I have removed gesture recognizer from the cell & put this into the main controller.