使用開源庫 SDWebImage 異步下載緩存圖片(持續更新)

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

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

Asynchronous image downloader with cache support with an UIImageView category

UIImageView的類目,支持異步圖片下載,支持緩存機制

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

這個庫給UIImageView提供類目,支持遠程下載圖片(從網絡上)

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

• 一個UIImageView的類目,給 Cocoa Touch 框架添加了異步下載遠程圖片以及管理圖片緩存的功能
• 一個圖片的異步下載器
• 一個內存 + 磁盤的緩存機制,並自動管理
• gif動畫支持
• WebP格式支持
• 後臺解壓圖片
• 確保一樣地 URL 不會重複的下載屢次
• 確保無效的 URL 不會重複的連接
• 確保主線程永遠不會阻塞
• 效果拔羣!
• 使用GCD以及要求ARC
• 支持64位系統

如下進行SDWebImage使用的教程解說.

1. 從地址 https://github.com/rs/SDWebImage 下載源碼,將源碼包中得 SDWebImage 文件夾拖入你的工程當中.

2. 頭文件較多,請新建一個 SDWebImage.h 的頭文件,寫如下代碼幷包含全部頭文件,添加到.pch文件中

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

//MKAnnotationView地圖的註解View緩存
#import "MKAnnotationView+WebCache.h"

//判斷NSData是否什麼類型的圖片(例如:jpg,png,gif)
#import "NSData+ImageContentType.h"

//是SDWebImage包的一部分
#import "SDImageCache.h"      //緩存相關
#import "SDWebImageCompat.h"  //組件相關
#import "SDWebImageDecoder.h" //解碼相關

//圖片下載以及下載管理器
#import "SDWebImageDownloader.h"
#import "SDWebImageDownloaderOperation.h"

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

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

//gif類目
#import "UIImage+GIF.h"

//圖片其餘類目
#import "UIImage+MultiFormat.h"
#import "UIImage+WebP.h"
#import "UIImageView+WebCache.h"

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

3. 正式開始講解怎麼使用

獨立的下載圖片的功能(沒有緩存機制)

    NSString *oneImageURL =
    @"http://wallpapers.wallbase.cc/rozne/wallpaper-573934.jpg";
    
    [[SDWebImageDownloader sharedDownloader] downloadImageWithURL:[NSURL URLWithString:oneImageURL]
                                                          options:0
     
     progress:^(NSInteger receivedSize, NSInteger expectedSize)
     {
         //此處爲下載進度
     }
     completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished)
     {
         //下載完成後進入這裏執行
     }];

分析:此方法爲單例模式,看其源碼

+ (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). 默認值.全部的下載操做將會進入串行線程池FIFO
     */
    SDWebImageDownloaderFIFOExecutionOrder,

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

若是僅僅看上面的部分,知道下載單例由串行線程池管理着,按照隊列執行,一次最多能執行兩個,但我在實際測試過程當中發現,並不像描述的那樣子......,好吧,就當作是併發執行的了(此處疑問有時間再解決)

獨立的下載圖片的功能(有緩存機制)

    NSString *oneImageURL =
    @"http://pic.cnitblog.com/avatar/607542/20140226182241.png";
    
    [[SDWebImageManager sharedManager] downloadWithURL:[NSURL URLWithString:oneImageURL]
                                               options:0
     
    progress:^(NSInteger receivedSize, NSInteger expectedSize)
    {
        //此處爲下載進度
    }
    completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished)
    {
        //下載完成後進入這裏執行
    }];

清除緩存文件

    [[SDImageCache sharedImageCache] clearDisk];

判斷本地緩存中是否存在網絡中的圖片

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

獲取緩存圖片張數

    [[SDImageCache sharedImageCache] getDiskCount];

獲取全部緩存圖片的總大小

    [[SDImageCache sharedImageCache] getSize];

直接從緩存中提取圖片

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

直接刪除緩存中得圖片

    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;
    }

-未完待續-