一、Web Image
This library provides a category for UIImageView with support for remote images coming from the web.
It provides:
- An
UIImageViewcategory adding web image and cache management to the Cocoa Touch framework - An asynchronous image downloader
- An asynchronous memory + disk image caching with automatic cache expiration handling
- Animated GIF support
- WebP format support
- A background image decompression
- A guarantee that the same URL won't be downloaded several times
- A guarantee that bogus URLs won't be retried again and again
- A guarantee that main thread will never be blockedPerformances!
- Use GCD and ARC
- Arm64 support
NOTE: Version 3.8 of SDWebImage requires iOS 7 or later (because of NSURLSession). Versions 3.7 to 3.0 requires iOS 5.1.1. If you need iOS < 5.0 support, please use the last 2.0 version.
Using UIImageView+WebCache category with UITableView
Just #import the UIImageView+WebCache.h header, and call the sd_setImageWithURL:placeholderImage: method from the tableView:cellForRowAtIndexPath: UITableViewDataSource method. Everything will be handled for you, from async downloads to caching management.
#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 sd_setImageWithURL: method to load the web image
[cell.imageView sd_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
With blocks, you can be notified about the image download progress and whenever the image retrieval has completed with success or not:
// Here we use the new provided sd_setImageWithURL: method to load the web image
[cell.imageView sd_setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"] placeholderImage:[UIImage imageNamed:@"placeholder.png"] completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
... completion code here ...
}];
Note: neither your success nor failure block will be call if your image request is canceled before completion.
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).
Here is a simple example of how to use SDWebImageManager:
SDWebImageManager *manager = [SDWebImageManager sharedManager];
[manager downloadImageWithURL:imageURL options:0 progress:^(NSInteger receivedSize, NSInteger expectedSize) {
// progression tracking code
} completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
if (image) {
// do something with image
}
}];
Using Asynchronous Image Downloader Independently
It's also possible to use the async image downloader independently:
SDWebImageDownloader *downloader = [SDWebImageDownloader sharedDownloader];
[downloader downloadImageWithURL:imageURL options:0 progress:^(NSInteger receivedSize, NSInteger expectedSize) {
// progression tracking code
} completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished) {
if (image && finished) {
// do something with image
}
}];
Using Asynchronous Image Caching Independently
It is also possible to use the async based image cache store independently. SDImageCache maintains a memory cache and an optional disk cache. Disk cache write operations are performed asynchronous so it doesn't add unnecessary latency to the UI.
The SDImageCache class provides a singleton instance for convenience but you can create your own instance if you want to create separated cache namespace.
To lookup the cache, you use the queryDiskCacheForKey:done:
method. If the method returns nil, it means the cache doesn't currently own the image. You are thus responsible for generating and caching it. The cache key is an application unique identifier for the image to cache. It is generally the absolute URL of the image.
SDImageCache *imageCache = [[SDImageCache alloc] initWithNamespace:@"myNamespace"];
[imageCache queryDiskCacheForKey:myCacheKey done:^(UIImage *image) {
// image is not nil if image was found
}];
By default SDImageCache will lookup the disk cache if an image can't be found in the memory cache. You can prevent this from happening by calling the alternative method imageFromMemoryCacheForKey:.
To store an image into the cache, you use the storeImage:forKey:method:
[[SDImageCache sharedImageCache] storeImage:myImage forKey:myCacheKey];
By default, the image will be stored in memory cache as well as on disk cache (asynchronously). If you want only the memory cache, use the alternative method storeImage:forKey:toDisk: with a negative third argument.
Using cache key filter
Sometime, you may not want to use the image URL as cache key because part of the URL is dynamic (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.
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];
return [url absoluteString];
};
// Your app init code... return YES;
}
2、Common Problems
Using dynamic image size with UITableViewCell
UITableView determines the size of the image by the first image set for a cell. If your remote images don't have the same size as your placeholder image, you may experience strange anamorphic scaling issue. The following article gives a way to workaround this issue:
http://www.wrichards.com/blog/2011/11/sdwebimage-fixed-width-cell-images/
Handle image refresh
SDWebImage does very aggressive caching by default. It ignores all kind of caching control header returned by the HTTP server and cache the returned images with no time restriction. It implies your images URLs are static URLs pointing to images that never change. If the pointed image happen to change, some parts of the URL should change accordingly.
If you don't control the image server you're using, you may not be able to change the URL when its content is updated. This is the case for Facebook avatar URLs for instance. In such case, you may use the SDWebImageRefreshCachedflag. This will slightly degrade the performance but will respect the HTTP caching control headers:
[imageView sd_setImageWithURL:[NSURL URLWithString:@"https://graph.facebook.com/olivier.poitrey/picture"]
placeholderImage:[UIImage imageNamed:@"avatar-placeholder.png"]
options:SDWebImageRefreshCached];
Add a progress indicator
See this category: https://github.com/JJSaccolo/UIActivityIndicator-for-SDWebImage
三、Installation
There are three ways to use SDWebImage in your project:
- using CocoaPods
- copying all the files into your project
- importing the project as a static library
PODFILE
platform :ios, '7.0'
pod 'SDWebImage', '~>3.8'
If you are using Swift, be sure to add use_frameworks!
and set your target to iOS 8+:
platform :ios, '8.0'
use_frameworks!
SUBSPECS
There are 3 subspecs available now: Core, MapKit and WebP (this means you can install only some of the SDWebImage modules. By default, you get just Core, so if you need WebP, you need to specify it).
Podfile example:
pod 'SDWebImage/WebP'
CARTFILE
github "rs/SDWebImage"
USAGE
Swift
If you installed using CocoaPods:
import SDWebImage
If you installed manually:
import WebImage
Objective-C
@import WebImage;
Installation by cloning the repository
In order to gain access to all the files from the repository, you should clone it.
git clone --recursive https://github.com/rs/SDWebImage.git
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
- 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", this is needed by the progressive download feature:
Add Linker Flag
Open the "Build Settings" tab, in the "Linking" section, locate the "Other Linker Flags" setting and add the "-ObjC" flag:
Alternatively, if this causes compilation problems with frameworks that extend optional libraries, such as Parse, RestKit or opencv2, instead of the -ObjC flag use:
-force_load SDWebImage.framework/Versions/Current/SDWebImage
If you're using Cocoa Pods and have any frameworks that extend optional libraries, such as Parsen RestKit or opencv2, instead of the -ObjC flag use:
-force_load $(TARGET_BUILD_DIR)/libPods.a
and this:
$(inherited)
Import headers in your source files
In the source files where you need to use the library, import the header file:
#import <SDWebImage/UIImageView+WebCache.h>
四、Future Enhancements
- LRU memory cache cleanup instead of reset on memory warning
