How to copy an image file from iOS Photo Library (ALAssetsLibrary) to the local directory of an App?

问题

I can get images from Photo Library through ALAssetsLibrary:

void (^assetEnumerator)(ALAsset *, NSUInteger, BOOL *) = ^(ALAsset *result, NSUInteger index, BOOL *stop){
        if([[result valueForProperty:ALAssetPropertyType] isEqualToString:ALAssetTypePhoto]) {
            // Copy the photo image to the `/Documents` directory of this App here

        }
    };

    void (^assetGroupEnumerator )(ALAssetsGroup*, BOOL*) = ^(ALAssetsGroup *group, BOOL *stop){
        if (group != nil) {
            [group enumerateAssetsUsingBlock:assetEnumerator];
        }
    };
    // fetch
    ALAssetsLibrary *library = [ALAssetsLibrary new];
    [library enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:assetGroupEnumerator failureBlock:^(NSError *error) {
        NSLog(@"failed");
    }];

I want to copy specific images to the local directory (App_home/Documents), but I don't know how to exactly do this job by handling ALAsset objects.

回答1:

Try with following Code

ALAssetsLibrary *assetLibrary=[[ALAssetsLibrary alloc] init];
[assetLibrary assetForURL:YourURL resultBlock:^(ALAsset *asset) 
    {
       ALAssetRepresentation *rep = [asset defaultRepresentation];
       Byte *buffer = (Byte*)malloc(rep.size);
       NSUInteger buffered = [rep getBytes:buffer fromOffset:0 length:rep.size error:nil];
       NSData *data = [NSData dataWithBytesNoCopy:buffer length:buffered freeWhenDone:YES];//this is NSData may be what you want
      [data writeToFile:photoFile atomically:YES];//you can save image later
   }
    failureBlock:^(NSError *err) 
    {
      NSLog(@"Error: %@",[err localizedDescription]);

    }
];

For get Image In document directory

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *newPath = [documentsDirectory stringByAppendingPathComponent:@"Your_Image_Name"];
UIImage *myImg = [UIImage imageWithContentsOfFile:newPath]

回答2:

It may be helpful to you . In this the outputFileURL is of type NSURL

   NSData *videoData = [NSData dataWithContentsOfURL:outputFileURL];

  [data writeToFile:destinationPath atomically:YES];//you can save image later

回答3:

You can get photo raw binary with below implementation and save to your target file.

+ (NSData *)photoAssetRawData:(ALAsset *)photoAsset error:(NSError **)error {
    ALAssetRepresentation *rep = photoAsset.defaultRepresentation;
    NSMutableData *data = [NSMutableData new];
    long long offset = 0;
    uint8_t dataBuffer[PHOTO_READ_CHUNK_SIZE];
    NSError *internalError;
    do {
        NSUInteger readByteLength = [rep getBytes:dataBuffer fromOffset:offset length:sizeof(dataBuffer) error:&internalError];
        if(internalError != nil) {
            if(error != NULL) {
                *error = internalError;
            }
            return nil;
        }
        offset += readByteLength;
        [data appendBytes:(void*)dataBuffer length:readByteLength];
    }
    while (offset < rep.size);
    return data;
}

One thing must be aware, this raw data has not applied any filter iOS default gallery App added, if you want these filter applied, you should get these XMP liked filter from [ALAssetRepresentation metadata] and create filters with [CIFilter filterArrayFromSerializedXMP:inputImageExtent:error:], then apply them on full resolution image, finally save this processed image as JPEG or PNG to file.

Below shows how to apply these filters.

+ (CGImageRef)applyXMPFilter:(ALAsset *)asset{
    ALAssetRepresentation *rep = [asset defaultRepresentation];
    CGImageRef imageRef = [rep fullResolutionImage];
    NSString *adjustmentXMP;
    NSData *adjustmentXMPData;
    NSError *__autoreleasing error = nil;
    NSArray *filters=nil;
    CGRect extend = CGRectZero;
    //add filter to image
    ALAssetRepresentation *representation = asset.defaultRepresentation;
    adjustmentXMP = [representation.metadata objectForKey:@"AdjustmentXMP"];
    adjustmentXMPData = [adjustmentXMP dataUsingEncoding:NSUTF8StringEncoding];
    extend.size = representation.dimensions;
    filters = [CIFilter filterArrayFromSerializedXMP:adjustmentXMPData inputImageExtent:extend error:&error];
    if(filters)
    {
        CIImage *image = [CIImage imageWithCGImage:imageRef];
        CIContext *context = [CIContext contextWithOptions:nil];
        for (CIFilter *filter in filters)
        {
            [filter setValue:image forKey:kCIInputImageKey];
            image = [filter outputImage];
        }
        imageRef = [context createCGImage:image fromRect:image.extent];
    }
    return imageRef;
}

来源：https://stackoverflow.com/questions/18734070/how-to-copy-an-image-file-from-ios-photo-library-alassetslibrary-to-the-local