Question

我正在写一本＆＃34;笔记本＆＃34;风格方案。笔记本有多个页面，我试图放入＆＃34;转到页面＆＃34; popover允许用户转到任何页面。弹出窗口显示每个页面缩略图的集合视图。显然，它会很棒：

在popover中单击所需的页面缩略图
通过委托发送selectedPage
让收件人mainViewController显示selectedPage

popover效果很好。页面选择工作并传回selectedPage。

问题是我需要有mainViewController＆＃34;等待＆＃34;供用户选择页面。这里是mainViewController中相关的代码部分：

用户选择barButton来显示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")
        }

我怀疑我在selectPage函数中需要某种闭包或处理程序，但我无法弄明白。希望足够清楚。现在是凌晨......

以下是popover的代码：

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
}

}

Answer 1

这是异步编程的典型示例。在这种情况下，您正在等待的异步事件是用户响应。

几乎普遍的答案是“不要等待。发送消息并让事件在完成后通知您。”

我要做的是创建一个UIViewController的自定义子类作为你的popover，并给popover一个完成块（closure）属性，或者用一个委托设置它，并定义一个协议，以便当用户选择一个选项时，popover可以通知它的委托。（这两种方法非常相似，但是使用完成块，您不必定义一个被调用的方法 - 当您进行调用弹出窗口的调用时，只需传入完成代码。）

如何＆＃34;等待＆＃39;要解除PopoverPresentationController

1 个答案: