disappearing headers in swift - ios

Question

I managed a way to animate my cells. I created a global variable named rowHeight in type of CGFloat and implicitly assigned it as 40. I wrote this code down:
func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
return rowHeight
}
In the touch event:
#IBAction func lessonCollapser(sender: AnyObject) {
if rowHeight == 40 {
self.tableView.beginUpdates()
UIView.animateWithDuration(1, animations: {self.rowHeight = 0})
self.tableView.endUpdates()
} else if rowHeight == 0 {
self.tableView.beginUpdates()
UIView.animateWithDuration(1, animations: {self.rowHeight = 40})
self.tableView.endUpdates()
}
}
So far so good. Even though it is being animated, there are a few problems.
First: My custom headers disappear.
Second: I get an error: "no index path for table cell being reused". I think because there are no index paths, the headers are disappeared. That is expected. What is not expected is that, why my tables' index paths disappeared when I used the animation? I think that is because of the beginUpdates() and endUpdates(). Can someone advice me something to do?
The code for my header view:
func tableView(tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
let headerCell = tableView.dequeueReusableCellWithIdentifier("HeaderCell") as! lessonHeaderTableViewCell
switch (section) {
default:
headerCell.lessonHeader.setTitle("TEST HEADER", forState: .Normal)
}
return headerCell
}
What happens on the code above is this: I created a prototype cell with "headerCell" identifier. I threw a button inside it. I created a swift file named "lessonHeaderTableViewCell. I assigned it as class of the prototype cell so it could control it. Lastly, I created an outlet named "lessonHeader" for the button, inside the swift file that I created.