Question

我正在努力做到以下几点我有一个数组，其中包含几个不同图像的URL。这些图像将显示在滚动视图中，我希望保留此顺序，以便能够删除特定索引处的特定图像现在我正在使用for循环，首先我用NSNull个对象加载数组，然后我运行循环用图像替换所有对象。这似乎并不真正有效，特别是当应用程序从后台加载时。

这是我的代码：

func downloadImagesfromUrlArray(){

    for var i=0;i < graphsURLlist.count; i++ {
        if let data = NSData(contentsOfURL: graphsURLlist[i]){
            let image = UIImage(data: data)
            pageImages.replaceObjectAtIndex(i, withObject: image!)
            //self.scaleImagesandScrollView()
        }else{
            NSLog("%@", i)
            var alert = myAlertController(title: nil, message: "Error trying to update the charts. Try again later \(i)",
                preferredStyle: UIAlertControllerStyle.Alert)


            alert.addAction(UIAlertAction(title: "Ok", style: UIAlertActionStyle.Default, handler: nil))
            self.presentViewController(alert, animated: true, completion: nil)
        }
        //Enter queue for every image to download
    }

    dispatch_group_leave(self.group)
}

有更好的方法吗？谢谢

Answer 1

您最好以异步方式下载图像并缓存它们。在下载图像之前，最好显示微调器，然后用图像替换它。

以下是我最新应用中的一些相关方法：

func downloadAndCacheImg(url: String?, cell: AppCell, tableView: UITableView, indexPath: NSIndexPath) {
    if url == nil { return }

    let charactersToRemove = NSCharacterSet.alphanumericCharacterSet().invertedSet
    let cacheFilename = "".join(url!.componentsSeparatedByCharactersInSet(charactersToRemove))

    if let fullFilename = prefixFilenameWithDirectory(cacheFilename), img = UIImage(named: fullFilename) {
        cell.setAppImage(img)
        return
    }
    if let nsUrl = NSURL(string: url!) {
        NSURLConnection.sendAsynchronousRequest(NSURLRequest(URL: nsUrl), queue: NSOperationQueue.mainQueue(), completionHandler: { (response, data, error) -> Void in
            if let data = data, img = UIImage(data: data) {
                if let fullFilename = self.prefixFilenameWithDirectory(cacheFilename) {
                    data.writeToFile(fullFilename, atomically: true)
                }
                if let cell = tableView.cellForRowAtIndexPath(indexPath) as? AppCell {
                    cell.setAppImage(img)
                }
            }
        })
    }
}

func prefixFilenameWithDirectory(filename: String) -> String? {
    var dir = NSFileManager.defaultManager().URLForDirectory(.CachesDirectory, inDomain: .UserDomainMask, appropriateForURL: nil, create: true, error: nil)
    dir = dir?.URLByAppendingPathComponent(filename)
    return dir?.path
}

iOS将图像保存到数组时保持url数组顺序

1 个答案: