Web image（网络图像）
该库提供了一个支持来自Web的远程图像的UIImageView类别
它提供了:
- 添加网络图像和缓存管理到Cocoa Touch framework的UIImageView类别
- 异步图像下载
- An asynchronous memory + disk image caching with automatic cache expiration handling
- 支持GIF动画
- 支持WebP格式
- 后台图像解压
- 保证相同的url不会下载多次
- 保证伪造的URL不会尝试一遍又一遍的下载
- 保证主线程永远不会被阻塞
- Performances!
- 使用GCD和ARC
注意：SDWebImage 3.0不向后兼容2.0并且最低需要iOS 5.0 的版本。如果你的iOS版本低于5.0，请使用2.0版本。
如何使用
API 文档地址 http://hackemist.com/SDWebImage/doc/。
Using UIImageView+WebCache category with UITableView
仅需引入 UIImageView+WebCache.h 头文件，在UITableViewDataSource的方法tableView:cellForRowAtIndexPath:中调用setImageWithURL:placeholderImage:方法。从异步下载到缓存管理，一切都会为你处理。
#import <SDWebImage/UIImageView+WebCache.h> ... - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *MyIdentifier = @"MyIdentifier"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier]; if (cell == nil)
{
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
reuseIdentifier:MyIdentifier] autorelease];
} // Here we use the new provided setImageWithURL: method to load the web image
[cell.imageView setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"]
placeholderImage:[UIImage imageNamed:@"placeholder.png"]]; cell.textLabel.text = @"My Text";
return cell;
}
Using blocks
// Here we use the new provided setImageWithURL: method to load the web image
[cell.imageView setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"]
placeholderImage:[UIImage imageNamed:@"placeholder.png"]
completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType) {... completion code here ...}];
Using SDWebImageManager
The SDWebImageManager is the class behind the UIImageView+WebCache category. It ties the asynchronous downloader with the image cache store. You can use this class directly to benefit from web image downloading with caching in another context than a UIView (ie: with Cocoa)
SDWebImageManager *manager = [SDWebImageManager sharedManager];
[manager downloadWithURL:imageURL
options:0
progress:^(NSUInteger receivedSize, long long expectedSize)
{
// progression tracking code
}
completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType)
{
if (image)
{
// do something with image
}
}];
[SDWebImageDownloader.sharedDownloader downloadImageWithURL:imageURL
options:0
progress:^(NSUInteger receivedSize, long long expectedSize)
{
// progression tracking code
}
completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished)
{
if (image && finished)
{
// do something with image
}
}];
SDImageCache *imageCache = [SDImageCache.alloc initWithNamespace:@"myNamespace"];
[imageCache queryDiskCacheForKey:myCacheKey done:^(UIImage *image)
{
// image is not nil if image was found
}];
[[SDImageCache sharedImageCache] storeImage:myImage forKey:myCacheKey];
Using cache key filter
有时你也许不想使用图像URL作为缓存键，因为URL可能是动态的(i.e.: for access control purpose)。SDWebImageManager provides a way to set a cache key filter that takes the NSURL as input, and output a cache key NSString（这句不大理解）。
下面的示例在应用程序的委托中设置一个过滤器，在使用它的缓存键之前将从URL中删除任何查询字符串（The following example sets a filter in the application delegate that will remove any query-string from the URL before to use it as a cache key）：
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
SDWebImageManager.sharedManager.cacheKeyFilter:^(NSURL *url)
{
url = [[[NSURL alloc] initWithScheme:url.scheme host:url.host path:url.path] autorelease];
return [url absoluteString];
}; // Your app init code...
return YES;
}
Using dynamic image size with UITableViewCell
UITableView通过第一个单元格设置的图像决定图像的尺寸。如果您的远程图像没有图像占位符的大小相同，您可能会遇到奇怪的变形缩放问题。下面的文章给出了一个方法来解决这个问题：
http://www.wrichards.com/blog/2011/11/sdwebimage-fixed-width-cell-images/
Handle image refresh（控制图像刷新）
默认情况下，SDWebImage确实非常积极的缓存。它忽略了所有类型的通过HTTP服务器返回的缓存控制头，并
如果你不控制你的图像服务器，当它的内容更新时你不能改变它的url。Facebook头像就是这种情况的例子。在这种情况下，你可以使用SDWebImageRefreshCached的标志。这将稍微降低性能，但将会考虑到HTTP缓存控制头：
[imageView setImageWithURL:[NSURL URLWithString:@"https://graph.facebook.com/olivier.poitrey/picture"]
placeholderImage:[UIImage imageNamed:@"avatar-placeholder.png"]
options:SDWebImageRefreshCached];
Add a progress indicator（添加进度指示）
查看这个类别： https://github.com/JJSaccolo/UIActivityIndicator-for-SDWebImage
Installation（安装）
Add the SDWebImage project to your project
- Download and unzip the last version of the framework from the download page
- Right-click on the project navigator and select "Add Files to "Your Project":
- In the dialog, select SDWebImage.framework:
- Check the "Copy items into destination group's folder (if needed)" checkbox
Add dependencies（添加依赖性）
- In you application project app’s target settings, find the "Build Phases" section and open the "Link Binary With Libraries" block:
- Click the "+" button again and select the "ImageIO.framework"(还缺一个“MapKit.framework”，readme中没提到), this is needed by the progressive download feature:
Add Linker Flag（添加链接标志）
Open the "Build Settings" tab, in the "Linking" section, locate the "Other Linker Flags" setting and add the "-ObjC" flag:
Import headers in your source files（导入头文件到你的资源文件中）
在你需要用到这个库的资源文件中导入下面的头文件：
#import <SDWebImage/UIImageView+WebCache.h>
Build Project（编译工程）
Future Enhancements（未来增强功能）
LRU memory cache cleanup instead of reset on memory warning