无法使用ALAssets返回的路径URL加载图像

Question

I am writing an image in iPad using ALAssets. When it finish I try to create an UIImage with the returned URL but it won't load. This is the code:

LAssetsLibrary *library = [[ALAssetsLibrary alloc] init];  
    [library writeImageToSavedPhotosAlbum:[anImage CGImage] orientation:(ALAssetOrientation)[anImage imageOrientation] completionBlock:^(NSURL *assetURL, NSError *error){  
        if (!error) {
            CGImageSourceRef src = CGImageSourceCreateWithURL((CFURLRef) [NSURL fileURLWithPath:[assetURL absoluteString]], NULL);

My purpose is to save an image to the device, then convert it to another format using ImageIO and finally send it to a web service. CGImageSourceRef is null, I also tried with standard UIImage with the same result.

What I am doing wrong here?

EDIT: The problem is when creating the CFURLRef. If I do

CGImageSourceCreateWithURL((CFURLRef) assetURL, NULL);

I got this error

ImageIO: CGImageSourceCreateWithURL CFURLCreateDataAndPropertiesFromResource failed with error code -11.

But if I try to convert the URL with

[NSURL fileURLWithPath:[assetURL absoluteString]]

the path is changed to

assets-library:/asset/asset.JPG%3Fid=57BBBA99-E7BF-4DB7-839E-F915005E6DFA&ext=JPG -- file://localhost/

I cannot find how to properly create the CFURLRef needed by the method. I tried printing all the conversions I could think of and this are the results

[assetURL relativePath]
[assetURL relativeString]
[assetURL absoluteURL]
[assetURL absoluteString]
 /asset.JPG ,
 assets-library://asset/asset.JPG?id=57BBBA99-E7BF-4DB7-839E-F915005E6DFA&ext=JPG
 assets-library://asset/asset.JPG?id=57BBBA99-E7BF-4DB7-839E-F915005E6DFA&ext=JPG
 assets-library://asset/asset.JPG?id=57BBBA99-E7BF-4DB7-839E-F915005E6DFA&ext=JPG

[NSURL fileURLWithPath:[assetURL relativePath]]
[NSURL fileURLWithPath:[assetURL relativeString]]
[NSURL fileURLWithPath:[assetURL absoluteString]]
file://localhost/asset.JPG
assets-library:/asset/asset.JPG%3Fid=57BBBA99-E7BF-4DB7-839E-F915005E6DFA&ext=JPG -- file://localhost/
assets-library:/asset/asset.JPG%3Fid=57BBBA99-E7BF-4DB7-839E-F915005E6DFA&ext=JPG -- file://localhost/

Help please, I am stuck with this :-(

Answer 1

This is what I did for my case.

    UIImage* anImage;   //this is the original image    
    NSData * imgData = UIImageJPEGRepresentation(anImage, 0.7);
    CGImageSourceRef src = CGImageSourceCreateWithData((CFDataRef) imgData, NULL);

    NSMutableData *data = [NSMutableData data];
    CFStringRef imageType = CFSTR("com.microsoft.bmp");
    CGImageDestinationRef myImageDest = CGImageDestinationCreateWithData((CFMutableDataRef) data, imageType, 1, nil);

    //Convert!
    CGImageDestinationAddImageFromSource(myImageDest, src, 0, myOptions);
    CGImageDestinationFinalize(myImageDest);
    //Freeing things
    CFRelease(myImageDest);
    CFRelease(src);

But this just converts the image, it doesn't store it in any file... Not sure this should be an answer to the original question.

Answer 2

If you already have an ALAsset and your goal is a CGImageRef you can do something like this.

ALAssetRepresentation* rep = [asset defaultRepresentation];

NSDictionary* options = [[NSDictionary alloc] initWithObjectsAndKeys:
                         (id)kCFBooleanTrue, (id)kCGImageSourceCreateThumbnailWithTransform,
                         (id)kCFBooleanTrue, (id)kCGImageSourceCreateThumbnailFromImageAlways, 
                         (id)[NSNumber numberWithDouble:400], (id)kCGImageSourceThumbnailMaxPixelSize, 
                         nil];

CGImageRef image = [rep CGImageWithOptions:options];