Swift: How to animate the rowHeight of a UITableView? - swift

Question

I'm trying to animate the height of tableViewCell rows by calling startAnimation() inside the tableView function:
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier(cellIdentifier, forIndexPath: indexPath) as! TableViewCell
tableView.rowHeight = 44.0
startAnimation(tableView)
return cell
}
//MARK: Animation function
func startAnimation(tableView: UITableView) {
UIView.animateWithDuration(0.7, delay: 1.0, options: .CurveEaseOut, animations: {
tableView.rowHeight = 88.0
}, completion: { finished in
print("Row heights changed!")
})
}
The result: The row height does change but without any animation occurring. I don't understand why the animation doesn't work. Should I perhaps define some beginning and end state somewhere?

Answer 1

Don't change the height that way. Instead, when you know you want to change the height of a cell, call (in whatever function):
self.tableView.beginUpdates()
self.tableView.endUpdates()
These calls notify the tableView to check for height changes. Then implement the delegate override func tableView(tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat, and provide the proper height for each cell. The change in height will be animated automatically. You can return UITableViewAutomaticDimension for items you don't have an explicit height for.
I would not suggest doing such actions from within cellForRowAtIndexPath, however, but in one that responds to a tap didSelectRowAtIndexPath, for example. In one of my classes, I do:
override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
if indexPath == self.selectedIndexPath {
self.selectedIndexPath = nil
}else{
self.selectedIndexPath = indexPath
}
}
internal var selectedIndexPath: NSIndexPath? {
didSet{
//(own internal logic removed)
//these magical lines tell the tableview something's up, and it checks cell heights and animates changes
self.tableView.beginUpdates()
self.tableView.endUpdates()
}
}
override func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
if indexPath == self.selectedIndexPath {
let size = //your custom size
return size
}else{
return UITableViewAutomaticDimension
}
}