swift - Swift:关闭以模态呈现的UICollectionViewController，传递数据

我在Swift项目的故事板中具有以下设置：



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，我具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)
}

如何将选定的颜色传递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

似乎即使实例化，backgroundView.backgroundColor也不可用。

我还尝试在dismissViewController的完成代码块中执行上述代码，并出现相同的错误：

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，我对此确实感到头疼。如果有任何不清楚的地方，请告诉我，我们将乐意提供更多信息。

最佳答案

This blog post包括完整的source code in Objective-C帮助我解决了问题。转换为Swift的相关代码段：

@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放松序列的有用说明。