Swift：如何在方法返回之前获取异步数据？

Question

I'm trying work use the following plugin for a grid layout. https://github.com/ecerney/CollectionViewWaterfallLayout

It requires me to return a cgsize for each cell with the actual image size.

So I'm trying to get to the size with another cocoapod plugin:

https://github.com/IMcD23/IMRemoteImageSize/

but, "getImageSize" is an async call to get the image I believe. Therefore each time return value for cgsize is "nil". Is there a way for me to get the size before the return function executes? Thanks!

func collectionView(collectionView: UICollectionView, layout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {

    let image = images[indexPath.row]

    var sizeOfTopCover:CGSize?

    UIImage.getImageSize(image.url, completion: {


        (size) -> Void in
        print("Got size of image: \(image.url): \(size)")

        sizeOfTopCover = size

    })

    return sizeOfTopCover! <<< breaking here

}

Answer 1

You must be know size when call

func collectionView(collectionView: UICollectionView, layout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize 

But you can reload your collection view when received sizes for all cells. Or reload each cell when you received size for cell.