Question

我有一个跟随视图控制器，其中嵌入了一个表格视图控制器。当我尝试从Firebase加载配置文件图像时，它加载得很好，但在向下或向上滚动时，它会与其余的配置文件图像保持互换状态。同样，当我点击表格视图单元格以跟随该特定用户时，指示（复选标记）也会出现在第四个单元格上。这是xcode中的错误吗我在Mac OS Sierra 10.12.6上使用Xcode 9.1

Answer 1

如果要从背景获取图像，请确保将每个图像分配给正确的单元格。一种实现方法是创建一个包含图像和唯一ID的自定义类，每当您要将图像分配给单元格时，请先检查ID以确保其正确。

关于复选标记错误，您可以尝试重置prepareForReuse()函数中的单元格。

编辑

由于您正在使用异步，因此无法保证将按顺序返回图像。因此，要将正确的图像放入正确的单元格中，您需要执行以下操作

//if the image is already fetched, you don't have to get it from firebase again
private var imageCache = [String:UIImage]()

//Create custom ImageView class that downloads image from url 
class CustomImageView: UIImageView{

var lastImageURL: String?

//call this function to get the right image with url
func setupWithImageURL(imageURL: String){
    self.contentMode = .scaleAspectFill
    self.clipsToBounds = true

    //keep track of the url of the right image
    lastImageURL = imageURL

    //check if the image is already there
    if let cachedImage = imageCache[imageURL]{
        self.image = cachedImage
        return
    }

    //if no image, get it with url
    guard let url = URL(string: imageURL) else {return}

    URLSession.shared.dataTask(with: url) { (data, response, err) in
        if let err = err{
            print("Unable to download data from database: ",err)
            return
        }

        guard let data = data else {return}
        guard let image = UIImage(data: data) else {return}
        imageCache[url.absoluteString] = image

        //if not the correct image, return and do nothing
        if (url.absoluteString != self.lastImageURL){
            return
        }

        //if the image is the correct one, set it to the imageView
        DispatchQueue.main.async {
            self.image = image
        }
    }.resume()
}

}

从模拟器中的Firebase加载后，图像不断变化

1 个答案: