原因

因為 SDWebImage 的緩存機制, 相同的 URL 它就認為可以去到沙盒里面的緩存路片

解決方法

NSString *testImageUrl = "www.你的image.com";
[_IMG sd_setImageWithURL:[NSURL URLWithString:testImageUrl] placeholderImage:[UIImage imageNamed:@"1.png"] options:SDWebImageRefreshCached];

SDWebImageManager.m文件中，大概176行左右吧，把之前的代碼：（如下）

if (image && options & SDWebImageRefreshCached) {
    // force progressive off if image already cached but forced refreshing
    downloaderOptions &= ~SDWebImageDownloaderProgressiveDownload;
    // ignore image read from NSURLCache if image if cached but force refreshing
    downloaderOptions |= SDWebImageDownloaderIgnoreCachedResponse;
}

更換成如下代碼：

if (image && options & SDWebImageRefreshCached) {
    // force progressive off if image already cached but forced refreshing
    downloaderOptions &= ~SDWebImageDownloaderProgressiveDownload;
    // remove SDWebImageDownloaderUseNSURLCache flag
    downloaderOptions &= ~SDWebImageDownloaderUseNSURLCache;
    // ignore image read from NSURLCache if image if cached but force refreshing
    downloaderOptions |= SDWebImageDownloaderIgnoreCachedResponse;
}