报错:Use of undeclared identifier '_executing' / '_finished'; 解决方法: 在SDWebImageDownloaderOperation类的实现中(@implementation里)添加: @synthesize executing = _executing; @synthesize finished = _finished; 示例: @implementation SDWebImageDownloaderOperation { size_t width, height; BOOL responseFromCached; } @synthesize executing = _executing; @synthesize finished = _finished;