SDWebImage源码解析一

前言

在用Swift写项目时，发现Kingfisher中可以对网络图片进行缩放并添加圆角等功能，感觉这个功能很实用。终于SDWebImage 5.0也有了这个功能。今天来讲一下SDWebImage的常用功能。

SDWebImage使用

先来看下面两个方法，你会发下下面这个方法中多了一个SDWebImageContext类型的参数。实现缩放和添加圆角等功能主要就是在这个参数上。

///以前常用方法
- (void)sd_setImageWithURL:(nullable NSURL *)url
          placeholderImage:(nullable UIImage *)placeholder
                   options:(SDWebImageOptions)options
///添加圆角功能使用方法
- (void)sd_setImageWithURL:(nullable NSURL *)url
          placeholderImage:(nullable UIImage *)placeholder
                   options:(SDWebImageOptions)options
                   context:(nullable SDWebImageContext *)context

SDWebImageContext这个进去你会发现这个其实是一个NSDictionary类型。
SDWebImageContextOption中有一个SDWebImageContextImageTransformer为key的值。这个key对应的值必须是id的对象。
SDWebImage中给我们提供了几个这种类

SDImagePipelineTransformer       //它可以将多个变换器绑定在一起，让图像按顺序逐个变换并生成最终图像
SDImageRoundCornerTransformer //圆角
SDImageResizingTransformer //调整大小
SDImageCroppingTransformer //裁剪
SDImageFlippingTransformer //翻转
SDImageRotationTransformer //旋转
SDImageTintTransformer //Tint颜色
SDImageBlurTransformer //毛玻璃效果
SDImageFilterTransformer //滤镜

需要实现调整大小并设置圆角的代码如下

    /// 圆角，这里的Radius和Size都是已像素为单位的，可以获取手机的Scale计算出具体大小
    SDImageRoundCornerTransformer *transformer1 = [SDImageRoundCornerTransformer transformerWithRadius:100 corners:UIRectCornerAllCorners borderWidth:0 borderColor:nil];
    /// 大小
    SDImageResizingTransformer *transformer2 = [SDImageResizingTransformer transformerWithSize:CGSizeMake(200, 200) scaleMode:(SDImageScaleModeAspectFill)];
    
    SDImagePipelineTransformer *transformer = [SDImagePipelineTransformer transformerWithTransformers:@[transformer1, transformer2]];
    
    [self.roundIV sd_setImageWithURL:url placeholderImage:nil options:SDWebImageRetryFailed context:@{ SDWebImageContextImageTransformer : transformer}];

另外SDWebImageOptions这个枚举有新增，有一个值我们可以用到SDWebImageAvoidDecodeImage防止解码图片。之前版本中防止加载高清大图导致内存暴涨一般采取的措施是如下设置（需要来回设置）。现在只需通过SDWebImageAvoidDecodeImage就可以了，方便很多。

[[SDImageCache sharedImageCache] setShouldDecompressImages:NO];
[[SDWebImageDownloader sharedDownloader] setShouldDecompressImages:NO];

SDWebImageDownloaderConfig下载配置

/// 用户名
[SDWebImageDownloader sharedDownloader].config.username = @"httpwatch";
/// 密码
[SDWebImageDownloader sharedDownloader].config.password = @"httpwatch01";
[[SDWebImageDownloader sharedDownloader] setValue:@"SDWebImage Demo" forHTTPHeaderField:@"AppName"];

/// 默认6个
[SDWebImageDownloader sharedDownloader].config.maxConcurrentDownloads = 6;
/// 默认15秒
[SDWebImageDownloader sharedDownloader].config.downloadTimeout = 15;

SDAnimatedImageView 加载动图

SDWebImageCacheKeyFilter 缓存路径过滤

有些图片后台返回的URL每次都不一样（如后面的参数不同），可以根据需求将该图片的存储路径进行过滤一下，可以不用每次都去下载

    SDWebImageCacheKeyFilter *filter = [SDWebImageCacheKeyFilter cacheKeyFilterWithBlock:^NSString * _Nullable(NSURL * _Nonnull url) {
        if (![url.absoluteString hasPrefix:@"https://ss0.bdstatic.com"]) {
            return url.absoluteString;
        }
//        NSURLComponents *otherUrl = [[NSURLComponents alloc] init];
//        otherUrl.scheme = url.scheme;
//        otherUrl.host = url.host;
//        otherUrl.path = url.path;
        return @"https://ss0.bdstatic.com";
    }];

    [SDWebImageManager sharedManager].cacheKeyFilter = filter;

    ///正确路径
    NSString *urlString = @"https://ss0.bdstatic.com/70cFvHSh_Q1YnxGkpoWK1HF6hhy/it/u=1307986195,877877609&fm=15&gp=0.jpg";
    NSURL *url = [NSURL URLWithString:urlString];
    
    [self.roundIV sd_setImageWithURL:url completed:^(UIImage * _Nullable image, NSError * _Nullable error, SDImageCacheType cacheType, NSURL * _Nullable imageURL) {
        NSLog(@"%f", image.size.width);
    }];
    
    ///不正确路径，但匹配缓存路径
    NSString *urlString1 = @"https://ss0.bdstatic.com/70cFvHSh_Q1YnxGkpoWK1HF6hhy.jpg";

    NSURL *url1 = [NSURL URLWithString:urlString1];
    [self.normalIV sd_setImageWithURL:url1 completed:^(UIImage * _Nullable image, NSError * _Nullable error, SDImageCacheType cacheType, NSURL * _Nullable imageURL) {
        NSLog(@"%f", image.size.width);
    }];

SDImageCache 缓存

/// 缓存图片
- (void)storeImage:(nullable UIImage *)image
         imageData:(nullable NSData *)imageData
            forKey:(nullable NSString *)key
            toDisk:(BOOL)toDisk
        completion:(nullable SDWebImageNoParamsBlock)completionBlock

/// 同步清理
- (void)clearMemory;

///异步清理
- (void)clearDiskOnCompletion:(nullable SDWebImageNoParamsBlock)completion;
/// 同步统计
- (NSUInteger)totalDiskSize;

/// 异步统计
- (void)calculateSizeWithCompletionBlock:(nullable SDImageCacheCalculateSizeBlock)completionBlock;