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

Question

我在Swift项目的故事板中有以下设置：

我有一个包含许多UIColor的数组：

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

用户可以单击“按钮”选项卡栏按钮，第二个VC将以模态显示（垂直封面）。从那里他可以从集合视图中选择一种颜色。第一个VC是UIViewController，第二个是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视图控制器？我试过了：

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Unexpectedly found nil while unwrapping Optional value

甚至在实例化时，backgroundView.backgroundColor似乎不可用。

我也尝试在dismissViewController的完成块中执行上面的代码，但同样的错误：

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]
    })
}

非常感谢任何建议，我真的对此感到失望。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。相关代码片段转换为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，以获取有关如何连接展开赛段的有用说明。