ios - swift 从 ALAsset 获取图像

Question

我有 ALAssetsLibrary 从相机返回的图像。现在，我想在 UIImageView 中显示它。我试过这段代码，但它显示了一些错误:

var assets : ALAsset = photoArray.objectAtIndex(indexPath.row) as ALAsset

cell.cameraOutlet.image = UIImage(CGImage: assets.thumbnail()) as UIImage // Showing error - Missing argument for parameter 'inBundle' in call 

在那之后，我尝试了这段代码:

var assets : ALAsset = (photoArray.objectAtIndex(indexPath.row) as ALAsset)
 var imageRef : CGImageRef = assets.thumbnail() as CGImageRef // showing error - Unmanaged<CGImage>, is not convertible to CGImageRef
 cell.cameraOutlet.image = UIImage(CGImage: assets.thumbnail()) as UIImage // Showing error - Missing argument for parameter 'inBundle' in call 

我想显示图片，我该怎么做？

dispatch_async(dispatch_get_main_queue(), {
self.photoLibrary.enumerateGroupsWithTypes(ALAssetsGroupType(ALAssetsGroupAlbum),
    usingBlock: {

        (group: ALAssetsGroup!, stop: UnsafePointer<ObjCBool>) -> Void in
        if group != nil {
            group.enumerateAssetsUsingBlock({
                (asset: ALAsset!, index: Int, stop: UnsafePointer<ObjCBool>) -> Void in

                if asset != nil
                {
                    if asset.valueForProperty(ALAssetPropertyType).isEqualToString(ALAssetTypePhoto)
                    {
                        self.photoArray.addObject(asset)
                    }
                }
                })
        }
        self.collectionView.reloadData()
    },
    failureBlock: {
        (myerror: NSError!) -> Void in
        println("error occurred: \(myerror.localizedDescription)")
    })
    })

override func numberOfSectionsInCollectionView(collectionView: UICollectionView!) -> Int {
        //#warning Incomplete method implementation -- Return the number of sections
        return photoArray.count
    }


    override func collectionView(collectionView: UICollectionView!, numberOfItemsInSection section: Int) -> Int {
        //#warning Incomplete method implementation -- Return the number of items in the section
        return 1
    }

    override func collectionView(collectionView: UICollectionView!, cellForItemAtIndexPath indexPath: NSIndexPath!) -> UICollectionViewCell! {
    let cell  : CameraCollectionViewCell = collectionView.dequeueReusableCellWithReuseIdentifier("Camera", forIndexPath: indexPath) as CameraCollectionViewCell

        var asset : ALAsset = photoArray.objectAtIndex(indexPath.row) as ALAsset
        cell.cameraOutlet.image = UIImage(CGImage: asset.thumbnail().takeUnretainedValue()) as UIImage
        return cell
    }

我认为输出仅显示一张图像 100 次。这段代码有什么问题？

Answer 1

thumbnail()函数返回 Unmanaged<CGImage> .如中所述 Working with Cocoa Data Types ，您必须使用 takeUnretainedValue() 将非托管对象转换为内存托管对象或 takeRetainedValue() .在这种情况下

cell.cameraOutlet.image = UIImage(CGImage: asset.thumbnail().takeUnretainedValue())

因为thumbnail()返回一个未保留的对象(没有“创建”或“复制”以其名称)。

swift 3:

cell.cameraOutlet.image = UIImage(cgImage: asset.thumbnail().takeUnretainedValue())

(但是，从 iOS 9 开始，资源库框架已弃用应该改用照片框架。)