Swift:解除模态呈现的 UICollectionViewController，传递数据

Question

我在 Swift 项目的 Storyboard 中进行了以下设置:

我有一个包含许多 UIColor 的数组:

let palette = [UIColor.greenColor(), UIColor.redColor(), ...]

用户可以点击“Button”选项卡栏按钮，第二个VC将以模态方式呈现(垂直覆盖)。从那里他可以从 Collection View 中选择一种颜色。第一个 VC 是 UIViewController，第二个 VC 是 UICollectionViewController。在第二个 VC 中，我有以下代码来处理颜色选择:

override func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath){
    println("select color with index \(indexPath.row)")
    //user selected color, dismiss modal view controller
    self.dismissViewControllerAnimated(true, completion: nil)
}

如何将所选颜色传回我的第一个 View Controller ？我尝试过:

override func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath){
    let vc = self.storyboard?.instantiateViewControllerWithIdentifier("FirstViewController") as FirstViewController
    // now, in FirstViewController, set backgroundColor of backgroundView with user selected value
    vc.backgroundView.backgroundColor = palette[indexPath.row]
    //user selected color, dismiss modal view controller
    self.dismissViewControllerAnimated(true, completion: nil)
}

上面的代码给了我在展开可选值时意外发现nil

似乎即使在实例化时，backgroundView.backgroundColor也不可用。

我也尝试在dismissViewController的完成 block 中执行上面的代码，出现同样的错误:

override func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath){
    //user selected color, dismiss modal view controller
    self.dismissViewControllerAnimated(true, completion: {
    let vc = self.storyboard?.instantiateViewControllerWithIdentifier("FirstViewController") as FirstViewController
    // now, in FirstViewController, set backgroundColor of backgroundView with user selected value
    vc.backgroundView.backgroundColor = palette[indexPath.row]
    })
}

非常感谢您的任何建议，我对此真的很困惑。如果有任何不清楚的地方，请告诉我，我很乐意提供更多信息。

Answer 1

This blog post包括完整source code in Objective-C帮助我解决了我的问题。相关代码片段翻译为 Swift:

@IBAction func unwindToSegue (segue : UIStoryboardSegue) {

    if segue.sourceViewController.isKindOfClass(BackgroundColorCollectionViewController) {
        let vc = segue.sourceViewController as BackgroundColorCollectionViewController
        if (vc.selectedColor != nil) {
            self.view.backgroundColor = vc.selectedColor
        }
    }

}

-

override func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath){
    println("select color with index \(indexPath.row)")
    self.selectedColor = palette[indexPath.row]
    self.performSegueWithIdentifier("colorSelected", sender: self)
}

如果您感到困惑，请务必观看视频，获取有关如何连接展开转场的有用说明。