iphone - 尝试从图像 I/O 创建 AspectRatioThumbnail 时出错

Question

我正在尝试为 iOS5 之前的 ALAsset 创建宽高比缩略图(ALAssetDefaultRepresentation aspectRatioThumbnail 直到 ios5 才实现)。我有以下代码，由于某种原因它给我一个错误:

CGImageRef imref;
    NSURL* url = [self.photoAsset.defaultRepresentation url];
    NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:
                       (id)kCFBooleanTrue, kCGImageSourceShouldAllowFloat,
                       (id)kCFBooleanTrue, kCGImageSourceCreateThumbnailWithTransform,
                       (id)kCFBooleanTrue, kCGImageSourceCreateThumbnailFromImageAlways,
                       [NSNumber numberWithInteger:1024], kCGImageSourceThumbnailMaxPixelSize, nil];
    CGImageSourceRef src = CGImageSourceCreateWithURL((CFURLRef)url, NULL);
    imref = CGImageSourceCreateThumbnailAtIndex(src, 0, (CFDictionaryRef) dictionary);

具体来说，我得到:

ImageIO: <ERROR>  CGImageSourceCreateWithURL CFURLCreateDataAndPropertiesFromResource failed with error code -11.ImageIO: <ERROR>  CGImageSourceCreateThumbnailAtIndex image source parameter is nil

有人知道这是怎么回事吗？

Answer 1

问题出在您为创建“src”而传递的url，检查 url 是否有效以及该 url 是否存在一些图像。