TableView reloadData resets scrollView contentOffset in header cell - swift

Question

I have a tableView with two custom cells. One for the header and one for the cells inside the tableView.
The Header cell looks like this:
Label Label ScrollView(inside scrollView is an imageView)
The other cell looks like this:
Label TextField ScrollView(inside scrollView is an imageView)
When I scroll one cell horizontally all other cells (including header cell) will get the same contentOffset. This works like a charm.
I added another function which adds another imageView inside the scrollView on top of the existing imageView for all cells except the header cel. Inside the new imageView I add a line which is draggable. This is realized by a longPressureGesture. Inside this gesture I need to do a tableView.reloadData() so that each time the line moves it will be updated for all cells. LongPressureGesture allows me to do this without loosing the control of the line while doing a reloadData().
But here is my problem:
The contentOffset of the scrollView inside the headerCell is reseted after calling reloadData() inside the longPressureGesture. But the contentOffset for all other scrollViews in the cells are still the same.
I tried to add the contentOffset in the headerCell so that each time the reloadData is called the contentOffset will be set. But this is not working because the contentOffset will be called to early and has no effect.
If I add a delay and then set the contentOffset again it is working. But this ends up in flickering which is not good.
Edit: Tried to use only one cell (used cell for header instead of specific header cell). Ended up with the same result. So this is an general issue for headers in tableView?
My code for the cells is:
/*
* This method fills all the given information for each signal to a custom cell by type SignalCell.
* Each cell has a signalName, a value at specific time and a wave image.
*/
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier(cellIdentifier, forIndexPath: indexPath) as! SignalCell
cell.delegate = self
// Get the signal for this row
let signal = VCDHelper.sharedInstance.signals[indexPath.row] as! VCDSignal
// Set the name of the signal to the label
cell.signalLabel.text = signal.name
cell.name = signal.name
// cellContainer is set inside renderWave every time a new Cell appears
renderTimePicker(cell, signal: signal, indexPath: indexPath)
renderWave(cell, signal: signal, indexPath: indexPath)
cellContainer.setObject(cell, forKey: signal.name)
return cell
}
Code for header:
// Display header cell
override func tableView(tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
let cell = tableView.dequeueReusableCellWithIdentifier(cellHeaderIdentifier) as! HeaderCell
// Add object to renderer dictionary
var headerRenderer = headerToRender.objectForKey("header") as? TimeRenderer
// Render waves
if let headerRenderer = headerRenderer {
cell.timeImageView.image = headerRenderer.renderedTime()
} else {
// There is no renderer yet
headerRenderer = TimeRenderer()
headerToRender.setObject(headerRenderer!, forKey: "header")
// Creates and returns an NSBlockOperation object with block
let operation = NSBlockOperation(block: { () -> Void in
let renderedHeaderImage = headerRenderer!.renderedTime()
NSOperationQueue.mainQueue().addOperationWithBlock({ () -> Void in
cell.timeImageView.image = renderedHeaderImage
cell.cellContainer = self.cellContainer
})
})
queue.addOperation(operation)
headerToRenderOperations.setObject(operation, forKey: "header")
}
cellContainer.setObject(cell, forKey: "header")
return cell
}
And here the code for saving/setting the contentOffset for each Cell realized in SignalCell class:
/*
* This method allows only horizontal scrolling.
* It also handles that scrolling out of bounds is not allowed
*/
func scrollViewDidScroll(scrollView: UIScrollView) {
// Set contentOffsetX to minimum bound value because we are out of range
if scrollView.contentOffset.x < 0 {
scrollCells(scrollView, contentOffsetX: 0.0)
VCDHelper.sharedInstance.waveScrollContentOffsetX = 0.0
}
if scrollView.contentOffset.x > 0 {
// ContentOffsetX is the point at the beginning of the scrollView
// We know the total size of the image and need to subtract the size of the scrollView
// This will result in the max contentOffset.x for scrolling
if scrollView.contentOffset.x <= CGFloat(VCDHelper.sharedInstance.imageWidth) - scrollView.bounds.width {
scrollCells(scrollView, contentOffsetX: scrollView.contentOffset.x)
VCDHelper.sharedInstance.waveScrollContentOffsetX = Float(scrollView.contentOffset.x)
} else {
// Set contentOffsetX to maximal bound value because we are out of range
scrollCells(scrollView, contentOffsetX: CGFloat(VCDHelper.sharedInstance.imageWidth) - scrollView.bounds.width)
}
}
}
/*
* This method scrolls all visible images inside the scrollView at once
*/
func scrollCells(scrollView: UIScrollView, contentOffsetX: CGFloat) {
for (key, cell) in self.cellContainer {
if key as! String == "header" {
let headerCell = cell as! HeaderCell
let scrollContentOffsetY = headerCell.timeScrollView.contentOffset.y
// Dont use setContentOffset because this will call scrollViewDidScroll each time
headerCell.timeScrollView.contentOffset = CGPoint(x: contentOffsetX, y: scrollContentOffsetY)
} else {
let signalCell = cell as! SignalCell
let scrollContentOffsetY = signalCell.signalScrollView.contentOffset.y
// Dont use setContentOffset because this will call scrollViewDidScroll each time
signalCell.signalScrollView.contentOffset = CGPoint(x: contentOffsetX, y: scrollContentOffsetY)
}
}
}