ios - 从 Assets 库的图像 url 代表转到 base64

Question

我最终试图将字典中的一组照片以 url rep 形式转换为 base64，以便通过 json 发送。

这是字典代码和它的日志:

    NSDictionary *dict = [self.form dictionaryWithValuesForKeys:keys];
    NSLog(@"dict::%@",dict);

NS日志:

dict::{   
    boardLodgingFurnished = "<null>";
    caption = "<null>";
    cars = "";
    photos =     (
                {
            caption = "";
            urlRep = "assets-library://asset/asset.JPG?id=CE8A426B-3B59-4172-8761-CC477F3BB3EE&ext=JPG";
        },
                {
            caption = "";
            urlRep = "assets-library://asset/asset.JPG?id=F4B68A42-1CA0-4880-9FB5-177CB091A28C&ext=JPG";
        }
    );
    yearsAtLocation = "";
    yearsInTheBusiness = "";
}

因此，对于字典中的每张照片，我想获取 urlRep 并将其转换为 base64 字符串，并在字典中用它替换 urlRep。

我现在所拥有的..不确定我是否朝着正确的方向前进:

for (id imageURL in [dict objectForKey:@"photos"])
{
ALAssetsLibrary *library = [ALAssetsLibrary new];
            ALAsset *ourAsset = [self assetForURL:imageURL withLibrary:library];

            /* Check out ALAssets */
            NSLog(@"%@", ourAsset);

            ALAssetRepresentation *representation = [ourAsset defaultRepresentation];
            CGImageRef imageRef = [representation fullResolutionImage];

            //TODO: Deal with JPG or PNG
            NSData *imageData = UIImageJPEGRepresentation([UIImage imageWithCGImage:imageRef], 0.1);
       NSLog(@"imagedata??%@",      [imageData base64EncodedString]);
//need to know how to add this back to dict
}

下面的方法是从上面调用的，但是在 while 循环中崩溃了

-[__NSDictionaryI scheme]: unrecognized selector sent to instance 0x166dd090
2014-01-03 10:57:27.361 Inspection App[2728:60b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSDictionaryI scheme]: unrecognized selector sent to instance 0x166dd090'

方法

- (ALAsset *)assetForURL:(NSURL *)url withLibrary:(ALAssetsLibrary *)assetsLibrary {
    __block ALAsset *result = nil;
    __block NSError *assetError = nil;
    dispatch_semaphore_t sema = dispatch_semaphore_create(0);

    [assetsLibrary assetForURL:url resultBlock:^(ALAsset *asset) {
        result = asset;
        dispatch_semaphore_signal(sema);
    } failureBlock:^(NSError *error) {
        assetError = error;
        dispatch_semaphore_signal(sema);
    }];


    if ([NSThread isMainThread]) {
        while (!result && !assetError) {
            [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
        }
    }
    else {
        dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
    }

    return result;
}

编辑:

if (photoUrls.count) {
            for (id photos in photoUrls){
            NSString *urlString = photos;
            [self base64ImageAtUrlString:urlString result:^(NSString *base64) {

                NSLog(@"imagedata??%@", base64);
            }];
        }
        }
        else {
            NSLog(@"where are my urls?");
        }

        NSMutableDictionary *jsonWithPhotos = [dict mutableCopy];

        [jsonWithPhotos setObject:convertedImages forKey:@"photo64"];
        NSLog(@"jjson photos::%@", jsonWithPhotos);

更新方法

- (void)base64ImageAtUrlString:(NSString *)urlString result:(void (^)(NSString *))completion {
    NSURL *url = [NSURL URLWithString:urlString];
    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];

    [library assetForURL:url resultBlock:^(ALAsset *asset) {

        // borrowing your code, here... didn't check it....
        ALAssetRepresentation *representation = [asset defaultRepresentation];
        CGImageRef imageRef = [representation fullResolutionImage];

        //TODO: Deal with JPG or PNG
        NSData *imageData = UIImageJPEGRepresentation([UIImage imageWithCGImage:imageRef], 0.1);
        NSString *base64 = [imageData base64EncodedString];
        completion(base64);
        [convertedImages addObject:base64];

//        NSLog(@"converted::%@",convertedImages);

    } failureBlock:^(NSError *error) {
        NSLog(@"that didn't work %@", error);
    }];
}

当我记录 jsonWithPhotos 时，对象 photo64 只是一个空白数组

Answer 1

崩溃是由于代码中关于字典的错误假设造成的。鉴于已发布的字典解析为 json 的描述，您需要像这样获取 url:

// collect the photo urls in an array
NSMutableArray *photoUrls = [NSMutableArray array];

// photos is an array of dictionaries in the dictionary
NSArray *photos = dict[@"photos"];
for (NSDictionary *photo in photos) {
    // photo is a dictionary containing a "caption" and a "urlRep"
    [photoUrls addObject:photo[@"urlRep"]];
}

现在您可以继续执行其工作只是转换的方法。您的问题可能包含更多有关如何执行此操作的问题。我建议从简单开始。看看你是否可以进行一次转换。通过从 base64 写回图像来测试它。

编辑 0:在不深入检查的情况下，我会将您的编码尝试重组为如下所示:

- (void)base64ImageAtUrlString:(NSString *)urlString result:(void (^)(NSString *))completion {
    NSURL *url = [NSURL URLWithString:urlString];
    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];

    [library assetForURL:url resultBlock:^(ALAsset *asset) {

        // borrowing your code, here... didn't check it....
        ALAssetRepresentation *representation = [asset defaultRepresentation];
        CGImageRef imageRef = [representation fullResolutionImage];

        //TODO: Deal with JPG or PNG
        NSData *imageData = UIImageJPEGRepresentation([UIImage imageWithCGImage:imageRef], 0.1);
        NSString *base64 = [imageData base64EncodedString];
        completion(base64);

    } failureBlock:^(NSError *error) {
        NSLog(@"that didn't work %@", error);
    }];
}

这样调用它:

if (photoUrls.count) {
    NSString *urlString = photoUrls[0];
    [self base64ImageAtUrlString:urlString result:^(NSString *base64) {
        NSLog(@"imagedata??%@", base64);
    }];
} else {
   NSLog(@"where are my urls?");
}

一旦它开始工作，看看你是否可以反转它，用 base64 数据制作一个图像。最后，一旦一切正常，您就可以处理潜在的内存问题。我的建议是考虑一次编码一个，一次将一个发送到服务器，然后释放其间的所有内容。

编辑 1 - 每个后续问题，如果您想用 base64 编码替换 url 数组中的所有 url，它可能会像这样(请记住，这可能会占用大量内存):

- (void)base64ImagesAtUrls:(NSMutableArray *)urls result:(void (^)(void))completion {

    __block NSInteger completed = 0;  // this is how we'll know that we're done
    // this approach doesn't depend on the asset library retrievals completing
    // sequentially, even though they probably will

    for (int i=0; i<urls.count; i++) {
        NSString *urlString = urls[i];
        [self base64ImageAtUrlString:urlString result:^(NSString *base64) {
            [urls replaceObjectAtIndex:i withObject:base64];
            if (++completed == urls.count) completion();
        }];
    }
}