使用开源库 SDWebImage 异步下载缓存图片(持续更新)

source https://github.com/rs/SDWebImage

APIdoc http://hackemist.com/SDWebImage/doc

Asynchronous image downloader with cache support with an UIImageView category

UIImageView的类目,支持异步图片下载,支持缓存机制

This library provides a category for UIImageVIew with support for remote images coming from the web.

这个库给UIImageView提供类目,支持远程下载图片(从网络上)

It provides:

An UIImageView category 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 blocked

Performances!

Use GCD and ARC

Arm64 support

一个UIImageView的类目,给 Cocoa Touch 框架添加了异步下载远程图片以及管理图片缓存的功能

一个图片的异步下载器

一个内存 + 磁盘的缓存机制,并自动管理

gif动画支持

WebP格式支持

后台解压图片

确保同样地 URL 不会重复的下载多次

确保无效的 URL 不会重复的链接

确保主线程永远不会阻塞

效果拔群!

使用GCD以及要求ARC

支持64位系统

以下进行SDWebImage使用的教程解说.

1. 从地址 https://github.com/rs/SDWebImage 下载源码,将源码包中得 SDWebImage 文件夹拖入你的工程当中.

2. 头文件较多,请新建一个 SDWebImage.h 的头文件,写以下代码并包含所有头文件,添加到.pch文件中

-------------------------------------------------------------------------------

//MKAnnotationView地图的注解View缓存
#import "MKAnnotationView+WebCache.h"

//判断NSData是否什么类型的图片(例如:jpg,png,gif)
#import "NSData+ImageContentType.h"

//是SDWebImage包的一部分
#import "SDImageCache.h" //缓存相关
#import "SDWebImageCompat.h" //组件相关
#import "SDWebImageDecoder.h" //解码相关

//图片下载以及下载管理器
#import "SDWebImageDownloader.h"
#import "SDWebImageDownloaderOperation.h"

//管理以及操作
#import "SDWebImageManager.h"
#import "SDWebImageOperation.h"

//UIButton类目
#import "UIButton+WebCache.h"

//gif类目
#import "UIImage+GIF.h"

//图片其他类目
#import "UIImage+MultiFormat.h"
#import "UIImage+WebP.h"
#import "UIImageView+WebCache.h"

-------------------------------------------------------------------------------

3. 正式开始讲解怎么使用

独立的下载图片的功能(没有缓存机制)

NSString *oneImageURL =
@"http://wallpapers.wallbase.cc/rozne/wallpaper-573934.jpg";

[[SDWebImageDownloader sharedDownloader] downloadImageWithURL:[NSURL URLWithString:oneImageURL]
options:0

progress:^(NSInteger receivedSize, NSInteger expectedSize)
{
//此处为下载进度
}
completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished)
{
//下载完成后进入这里执行
}];

分析:此方法为单例模式,看其源码

+ (SDWebImageDownloader *)sharedDownloader {
static dispatch_once_t once;
static id instance;
dispatch_once(&once, ^{
instance = [self new];
});
return instance;
}

- (id)init {
if ((self = [super init])) {
_executionOrder = SDWebImageDownloaderFIFOExecutionOrder;
_downloadQueue = [NSOperationQueue new];
_downloadQueue.maxConcurrentOperationCount = 2;
_URLCallbacks = [NSMutableDictionary new];
_HTTPHeaders = [NSMutableDictionary dictionaryWithObject:@"image/webp,image/*;q=0.8" forKey:@"Accept"];
_barrierQueue = dispatch_queue_create("com.hackemist.SDWebImageDownloaderBarrierQueue", DISPATCH_QUEUE_CONCURRENT);
_downloadTimeout = 15.0;
}
return self;
}

typedef NS_ENUM(NSInteger, SDWebImageDownloaderExecutionOrder) {
/**
* Default value. All download operations will execute in queue style (first-in-first-out). 默认值.所有的下载操作将会进入串行线程池FIFO
*/
SDWebImageDownloaderFIFOExecutionOrder,

/**
* All download operations will execute in stack style (last-in-first-out).
*/
SDWebImageDownloaderLIFOExecutionOrder
};

如果仅仅看上面的部分,知道下载单例由串行线程池管理着,按照队列执行,一次最多能执行两个,但我在实际测试过程中发现,并不像描述的那样子......,好吧,就当做是并发执行的了(此处疑问有时间再解决)

独立的下载图片的功能(有缓存机制)

NSString *oneImageURL =
@"http://pic.cnitblog.com/avatar/607542/20140226182241.png";

[[SDWebImageManager sharedManager] downloadWithURL:[NSURL URLWithString:oneImageURL]
options:0

progress:^(NSInteger receivedSize, NSInteger expectedSize)
{
//此处为下载进度
}
completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished)
{
//下载完成后进入这里执行
}];

清除缓存文件

[[SDImageCache sharedImageCache] clearDisk];

判断本地缓存中是否存在网络中的图片

NSString *imageNetURL = @"http://pic.cnitblog.com/avatar/607542/20140226182241.png";
[[SDImageCache sharedImageCache] diskImageExistsWithKey:imageNetURL];

获取缓存图片张数

[[SDImageCache sharedImageCache] getDiskCount];

获取所有缓存图片的总大小

[[SDImageCache sharedImageCache] getSize];

直接从缓存中提取图片

NSString *imageNetURL = @"http://pic.cnitblog.com/avatar/607542/20140226182241.png";
[[SDImageCache sharedImageCache] imageFromDiskCacheForKey:imageNetURL];

直接删除缓存中得图片

NSString *imageNetURL = @"http://pic.cnitblog.com/avatar/607542/20140226182241.png";
[[SDImageCache sharedImageCache] removeImageForKey:imageNetURL];

在UITableView中使用

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *MyIdentifier = @"Y.X.";

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 = @"Y.X.";
return cell;
}

-未完待续-