源碼閱讀：AFNetworking（十三）——UIImageView+AFNetworking

時間 2019-11-25

標籤源碼閱讀 afnetworking 十三 uiimageview+afnetworking uiimageview 简体版

原文原文鏈接

該文章閱讀的AFNetworking的版本爲3.2.0。緩存

這個分類是爲UIImageView添加異步加載網絡圖片的方法bash

1.接口方法

圖片下載器的訪問方法

/**
 設置用於下載圖片的圖片下載器
 */
+ (void)setSharedImageDownloader:(AFImageDownloader *)imageDownloader;

/**
 獲取用於下載圖片的圖片下載器
 */
+ (AFImageDownloader *)sharedImageDownloader;
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爲圖片視圖設置圖片的方法

/**
 爲圖片視圖設置指定圖片連接的圖片
 */
- (void)setImageWithURL:(NSURL *)url;

/**
 爲圖片視圖設置指定圖片連接的圖片，以及指定佔位圖
 */
- (void)setImageWithURL:(NSURL *)url
       placeholderImage:(nullable UIImage *)placeholderImage;

/**
 爲圖片視圖設置指定圖片連接、指定佔位圖以及指定成功與失敗回調block的圖片
 */
- (void)setImageWithURLRequest:(NSURLRequest *)urlRequest
              placeholderImage:(nullable UIImage *)placeholderImage
                       success:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, UIImage *image))success
                       failure:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, NSError *error))failure;

/**
 取消當前圖片下載任務
 */
- (void)cancelImageDownloadTask;
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2.UIImageView+_AFNetworking私有分類

2.1.接口

/**
 用於保存下載封裝對象
 */
@property (readwrite, nonatomic, strong, setter = af_setActiveImageDownloadReceipt:) AFImageDownloadReceipt *af_activeImageDownloadReceipt;
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2.2.實現

實現裏的兩個方法就是經過Runtime的關聯對象爲分類添加屬性保存下載封裝對象網絡

- (AFImageDownloadReceipt *)af_activeImageDownloadReceipt {
    return (AFImageDownloadReceipt *)objc_getAssociatedObject(self, @selector(af_activeImageDownloadReceipt));
}

- (void)af_setActiveImageDownloadReceipt:(AFImageDownloadReceipt *)imageDownloadReceipt {
    objc_setAssociatedObject(self, @selector(af_activeImageDownloadReceipt), imageDownloadReceipt, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
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3.方法實現

屬性的訪問方法

這兩個方法一樣是經過關聯對象爲分類添加屬性保存圖片下載對象異步

+ (AFImageDownloader *)sharedImageDownloader {
    return objc_getAssociatedObject(self, @selector(sharedImageDownloader)) ?: [AFImageDownloader defaultInstance];
}

+ (void)setSharedImageDownloader:(AFImageDownloader *)imageDownloader {
    objc_setAssociatedObject(self, @selector(sharedImageDownloader), imageDownloader, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
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設置圖片的方法

- (void)setImageWithURL:(NSURL *)url {
    // 調用下面的方法
    [self setImageWithURL:url placeholderImage:nil];
}

- (void)setImageWithURL:(NSURL *)url
       placeholderImage:(UIImage *)placeholderImage
{
    // 經過圖片連接生成請求對象，而後調用下面的方法
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request addValue:@"image/*" forHTTPHeaderField:@"Accept"];

    [self setImageWithURLRequest:request placeholderImage:placeholderImage success:nil failure:nil];
}

- (void)setImageWithURLRequest:(NSURLRequest *)urlRequest
              placeholderImage:(UIImage *)placeholderImage
                       success:(void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, UIImage *image))success
                       failure:(void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, NSError *error))failure
{
    
    // 若是請求對象的連接爲空，就取消掉以前的圖片下載任務，展現佔位圖，返回結束
    if ([urlRequest URL] == nil) {
        [self cancelImageDownloadTask];
        self.image = placeholderImage;
        return;
    }

    // 若是這個網絡請求正在進行中就不重複執行了
    if ([self isActiveTaskURLEqualToURLRequest:urlRequest]){
        return;
    }

    // 取消掉以前的圖片下載任務
    [self cancelImageDownloadTask];

    // 獲取圖片下載器對象
    AFImageDownloader *downloader = [[self class] sharedImageDownloader];
    // 獲取圖片下載器對象中的圖片緩存對象
    id <AFImageRequestCache> imageCache = downloader.imageCache;

    // 從圖片緩存對象中獲取緩存圖片
    UIImage *cachedImage = [imageCache imageforRequest:urlRequest withAdditionalIdentifier:nil];
    // 若是有緩存圖片
    if (cachedImage) {
        // 若是設置了成功回調block就調用block，不然就直接設置圖片
        if (success) {
            success(urlRequest, nil, cachedImage);
        } else {
            self.image = cachedImage;
        }
        [self clearActiveDownloadInformation];
    // 若是沒有緩存圖片
    } else {
        // 若是設置了佔位圖就展現佔位圖
        if (placeholderImage) {
            self.image = placeholderImage;
        }

        // 獲取UUID，生成下載封裝對象，並開始下載
        __weak __typeof(self)weakSelf = self;
        NSUUID *downloadID = [NSUUID UUID];
        AFImageDownloadReceipt *receipt;
        receipt = [downloader
                   downloadImageForURLRequest:urlRequest
                   withReceiptID:downloadID
                   success:^(NSURLRequest * _Nonnull request, NSHTTPURLResponse * _Nullable response, UIImage * _Nonnull responseObject) {
                       __strong __typeof(weakSelf)strongSelf = weakSelf;
                       // 若是是當前控件發起的任務
                       if ([strongSelf.af_activeImageDownloadReceipt.receiptID isEqual:downloadID]) {
                           // 若是設置了成功回調block就調用block，不然就直接設置圖片
                           if (success) {
                               success(request, response, responseObject);
                           } else if(responseObject) {
                               strongSelf.image = responseObject;
                           }
                           // 清除該控件的下載任務信息
                           [strongSelf clearActiveDownloadInformation];
                       }

                   }
                   failure:^(NSURLRequest * _Nonnull request, NSHTTPURLResponse * _Nullable response, NSError * _Nonnull error) {
                       __strong __typeof(weakSelf)strongSelf = weakSelf;
                        // 若是是當前控件發起的任務
                        if ([strongSelf.af_activeImageDownloadReceipt.receiptID isEqual:downloadID]) {
                            // 若是設置了失敗回調block就調用block
                            if (failure) {
                                failure(request, response, error);
                            }
                            // 清除該控件的下載任務信息
                            [strongSelf clearActiveDownloadInformation];
                        }
                   }];

        // 使用屬性保存生成的下載封裝對象
        self.af_activeImageDownloadReceipt = receipt;
    }
}

- (void)cancelImageDownloadTask {
    // 若是當前有下載任務
    if (self.af_activeImageDownloadReceipt != nil) {
        // 經過任務封裝對象將下載任務取消
        [[self.class sharedImageDownloader] cancelTaskForImageDownloadReceipt:self.af_activeImageDownloadReceipt];
        // 清除該控件的下載任務信息
        [self clearActiveDownloadInformation];
     }
}

- (void)clearActiveDownloadInformation {
    // 將保存下載封裝對象的屬性置空
    self.af_activeImageDownloadReceipt = nil;
}

- (BOOL)isActiveTaskURLEqualToURLRequest:(NSURLRequest *)urlRequest {
    // 判斷屬性中保存的下載封裝對象的下載連接和傳入的請求對象下載連接是否相同
    return [self.af_activeImageDownloadReceipt.task.originalRequest.URL.absoluteString isEqualToString:urlRequest.URL.absoluteString];
}
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