我可以从URL加载UIImage吗？

Question

我有一个图像的URL(从UIImagePickerController获取)但我不再拥有内存中的图像(该URL是从以前的应用程序运行中保存的).我可以再次从URL重新加载UIImage吗？

我看到UIImage有一个imageWithContentsOfFile:但我有一个URL.我可以使用NSData的dataWithContentsOfURL:来读取URL吗？

EDIT1

---

根据@ Daniel的回答,我尝试了以下代码,但它不起作用......

NSLog(@"%s %@", __PRETTY_FUNCTION__, photoURL);     
if (photoURL) {
    NSURL* aURL = [NSURL URLWithString:photoURL];
    NSData* data = [[NSData alloc] initWithContentsOfURL:aURL];
    self.photoImage = [UIImage imageWithData:data];
    [data release];
}

当我运行它时控制台显示:

-[PhotoBox willMoveToWindow:] file://localhost/Users/gary/Library/Application%20Support/iPhone%20Simulator/3.2/Media/DCIM/100APPLE/IMG_0004.JPG
*** -[NSURL length]: unrecognized selector sent to instance 0x536fbe0
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSURL length]: unrecognized selector sent to instance 0x536fbe0'

查看调用堆栈,我调用URLWithString,调用URLWithString:relativeToURL:,然后是initWithString:relativeToURL:,然后是_CFStringIsLegalURLString,然后是CFStringGetLength,然后是forwarding_prep_0,然后转发,然后调用 - [NSObject doesNotRecognizeSelector].

我的NSString(photoURL的地址是0x536fbe0)没有响应长度的任何想法？为什么它说它没有响应 - [NSURL长度]？难道不知道param是NSString,而不是NSURL吗？

EDIT2

---

好的,代码的唯一问题是字符串到URL的转换.如果我硬编码字符串,其他一切工作正常.所以我的NSString有问题,如果我无法弄清楚,我想这应该是一个不同的问题.插入此行(我从上面的控制台日志粘贴路径),它工作正常:

photoURL = @"file://localhost/Users/gary/Library/Application%20Support/iPhone%20Simulator/3.2/Media/DCIM/100APPLE/IMG_0004.JPG";

Answer 1

你可以这样做(同步,但紧凑):

UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:MyURL]]];

更好的方法是使用Apple的LazyTableImages来保持交互性.

Answer 2

您可以尝试SDWebImage,它提供:

1. 异步加载
2. 缓存供离线使用
3. 放置持有者图像以在加载时显示
4. 适用于UITableView

快速举例:

    [cell.imageView setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"] placeholderImage:[UIImage imageNamed:@"placeholder.png"]];

Answer 3

而迅捷的版本:

   let url = NSURL.URLWithString("http://live-wallpaper.net/iphone/img/app/i/p/iphone-4s-wallpapers-mobile-backgrounds-dark_2466f886de3472ef1fa968033f1da3e1_raw_1087fae1932cec8837695934b7eb1250_raw.jpg");
    var err: NSError?
    var imageData :NSData = NSData.dataWithContentsOfURL(url,options: NSDataReadingOptions.DataReadingMappedIfSafe, error: &err)
    var bgImage = UIImage(data:imageData)

Answer 4

获取DLImageLoader并尝试下面的代码

   [DLImageLoader loadImageFromURL:imageURL
                          completed:^(NSError *error, NSData *imgData) {
                              imageView.image = [UIImage imageWithData:imgData];
                              [imageView setContentMode:UIViewContentModeCenter];

                          }];

使用DLImageLoader的另一个典型的现实例子,它可以帮助某人...

PFObject *aFacebookUser = [self.fbFriends objectAtIndex:thisRow];
NSString *facebookImageURL = [NSString stringWithFormat:
    @"http://graph.facebook.com/%@/picture?type=large",
    [aFacebookUser objectForKey:@"id"] ];

__weak UIImageView *loadMe = self.userSmallAvatarImage;
// ~~note~~ you my, but usually DO NOT, want a weak ref
[DLImageLoader loadImageFromURL:facebookImageURL
   completed:^(NSError *error, NSData *imgData)
    {
    if ( loadMe == nil ) return;

    if (error == nil)
        {
        UIImage *image = [UIImage imageWithData:imgData];
        image = [image ourImageScaler];
        loadMe.image = image;
        }
    else
        {
        // an error when loading the image from the net
        }
    }];

正如我上面提到的那样,Haneke是另一个值得考虑的重要图书馆(不幸的是它不是轻量级的).

Answer 5

如果你是真的,绝对是积极肯定的NSURL是一个文件的URL,即[url isFileURL]是保证在你的情况下返回true,那么你可以简单地使用:

[UIImage imageWithContentsOfFile:url.path]

Answer 6

尝试使用此代码,您可以使用它设置加载图像,以便用户知道您的应用正在从网址加载图片:

UIImageView *yourImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"loading.png"]];
    [yourImageView setContentMode:UIViewContentModeScaleAspectFit];

    //Request image data from the URL:
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSData *imgData = [NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://yourdomain.com/yourimg.png"]];

        dispatch_async(dispatch_get_main_queue(), ^{
            if (imgData)
            {
                //Load the data into an UIImage:
                UIImage *image = [UIImage imageWithData:imgData];

                //Check if your image loaded successfully:
                if (image)
                {
                    yourImageView.image = image;
                }
                else
                {
                    //Failed to load the data into an UIImage:
                    yourImageView.image = [UIImage imageNamed:@"no-data-image.png"];
                }
            }
            else
            {
                //Failed to get the image data:
                yourImageView.image = [UIImage imageNamed:@"no-data-image.png"];
            }
        });
    });