I am writing a "notebook" style program. Notebooks have multiple pages and I am trying to put in a "go to page" popover to allow the user to go to any page. The popover presents a collectionView of thumbnails of each page. Obviously, it would be great to:
The popover works great. The page selection works and passes the selectedPage back.
The problem is that I need to have the mainViewController "wait" for the user to select a page. Here the relevant sections of code in the mainViewController:
User selects barButton to show popover:
@IBAction func selectPage(sender: UIBarButtonItem) {
self.performSegueWithIdentifier("showPages", sender: self)
//need to wait here for the popover to be dismissed.
//the next line is executed before segue even appears
//"while" and delay don't work
imageView.image = currentNotebook.pages[goToPage! - 1] //displays selectedPage (goToPage is set by delegation)
goToPage = nil
}
//segue to popover
case "showPages" :
let navigationController = segue.destinationViewController as? PageCollectionViewController
if let vc = navigationController {
vc.delegate = self
vc.modalInPopover = false
vc.preferredContentSize = CGSizeMake(400,100)
vc.notebook = self.currentNotebook
print("got to show pages")
}
I suspect I need some sort of closure or handler in the selectPage function, but I can't figure it out. Hope that is clear enough. It is very early in the morning...
Here is the code for the popover:
import UIKit
protocol PageCollectionViewControllerDelegate {
func selectsPage(selectedPage:Int)
}
class PageCollectionViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate {
var notebook: Notebook!
var pageNum: Int!
var delegate: PageCollectionViewControllerDelegate?
@IBOutlet weak var pageCollectionView: UICollectionView!
override func viewDidLoad() {
super.viewDidLoad()
self.pencilCollectionView!.registerClass(UICollectionViewCell.self, forCellWithReuseIdentifier: "cell")
// Do any additional setup after loading the view.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func numberOfSectionsInCollectionView(pageCollectionView: UICollectionView) -> Int {
return 1
}
func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return notebook.pages.count
}
func collectionView(pageCollectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
let cell = pageCollectionView.dequeueReusableCellWithReuseIdentifier("cell", forIndexPath: indexPath) as! PageCollectionViewCell
let cellImage = notebook.pages[indexPath.row]
let tempThumb = imageWithImage(cellImage, scaledToFillSize: CGSizeMake(cell.bounds.width, cell.bounds.height)) //create thumbnail of each page
cell.pageThumb.image = tempThumb
cell.backgroundColor = UIColor.whiteColor()
return cell
}
func collectionView(pageCollectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
//return page number
if let delegate = self.delegate {
pageNum = indexPath.row + 1
print("page number",pageNum)
delegate.selectsPage(pageNum)
}
self.dismissViewControllerAnimated(true, completion: nil) //if you comment this out the popover is not dismissed when clicking on a cell
}
func imageWithImage(image: UIImage, scaledToFillSize size: CGSize) -> UIImage {
let scale: CGFloat = max(size.width / image.size.width, size.height / image.size.height)
let width: CGFloat = image.size.width * scale
let height: CGFloat = image.size.height * scale
let imageRect: CGRect = CGRectMake((size.width - width) / 2.0, (size.height - height) / 2.0, width, height)
UIGraphicsBeginImageContextWithOptions(size, false, 0)
image.drawInRect(imageRect)
let newImage: UIImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return newImage
}
}
This is a typical example of async programming. In this case, the async event you're waiting for is a user response.
The almost universal answer is "don't wait. Send a message and have the event notify you when it's done."
What I would do is create a custom subclass of UIViewController as your popover, and either give the popover a completion block (closure) property, or set it up with a delegate, and define a protocol so that the popover can notify it's delegate when the user selects an option. (The two approaches are quite similar, but with a completion block you don't have to define a method that gets invoked - you just pass in your completion code when you make the call that invokes the popover.)