Threads, tasks, and the Objective-C SDK

@Robert S: I wouldn't recommend using `sleep` like that. I'd instead maintain references to each task object and then `cancel` each task object when the user cancels. I took a bit of time and wrote up what a solution might look like. It took me longer than I thought, which might be an indication that the SDK needs richer functionality.

Try this out and let me know how it works. I think it might be easier pulling the file directly: DownloadFolder.m

@interface MyClass ()

@property (atomic) DropboxClient * _Nullable client;
@property (atomic) NSOperationQueue * _Nullable responseQueue;
@property (atomic) NSFileManager * _Nullable fileManager;

@property (atomic) BOOL shouldContinue;
@property (atomic) NSLock *shouldContinueLock;

@property (atomic) NSMutableDictionary<NSString *, DBRpcTask *> *rpcTasks;
@property (atomic) NSMutableDictionary<NSString *, DBDownloadUrlTask *> *downloadUrlTasks;
@property (atomic) NSLock *tasksLock;

@end

 

@implementation MyClass

- (void)initAndLaunch {
  NSLog(@"\n\n\nInitializing on: %@", [NSThread currentThread]);

  _client = [DropboxClientsManager authorizedClient];
  _responseQueue = [NSOperationQueue new];
  [_responseQueue setMaxConcurrentOperationCount:1];
  _fileManager = [NSFileManager defaultManager];

  _shouldContinue = YES;
  _shouldContinueLock = [NSLock new];

  _rpcTasks = [NSMutableDictionary new];
  _downloadUrlTasks = [NSMutableDictionary new];
  _tasksLock = [NSLock new];

  NSURL *outputUrl = [_fileManager URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask][0];
  outputUrl = [outputUrl URLByAppendingPathComponent:[NSString stringWithFormat:@"%@.%@", @"MyOutputFolder", [NSUUID UUID].UUIDString]];

  [self downloadFolder:@" outputUrl:outputUrl];

  // cancel the download after 5 seconds
  double delayInSeconds = 5.0;
  dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
  dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
    [self cancelDownload];
  });
}

- (void)downloadFolder:(NSString *)inputPath outputUrl:(NSURL *)outputUrl {
  NSLog(@"Downloading all files from: \"%@\" to \"%@\", inputPath, outputUrl);
  [_responseQueue addOperationWithBlock:^{
    [self downloadFolderHelper:inputPath outputUrl:outputUrl];
  }];
}

- (void)downloadFolderHelper:(NSString *)inputPath outputUrl:(NSURL *)outputUrl {
  NSLog(@"Commencing folder download on: %@", [NSThread currentThread]);

  NSString *listFolderTaskKey = [NSString stringWithFormat:@"ListFolderTask.%@", [NSUUID UUID].UUIDString];

  [self.shouldContinueLock lock];

  if (!_shouldContinue) {
    NSLog(@"No longer continuing...");
    [self.shouldContinueLock unlock];
    return;
  }

  DBRpcTask *listFolderTask = [self listFolder:inputPath outputUrl:outputUrl listFolderTaskKey:listFolderTaskKey];

  [self.rpcTasks setObject:listFolderTask forKey:listFolderTaskKey];
  [self.shouldContinueLock unlock];
}

-(DBRpcTask *)listFolder:(NSString *)inputPath outputUrl:(NSURL *)outputUrl listFolderTaskKey:(NSString *)listFolderTaskKey {
  DBRpcTask *listFolderTask = [[_client.filesRoutes listFolder:inputPath]
   response:_responseQueue response:^(DBFILESListFolderResult *listFolderResult, DBFILESListFolderError *routeError, DBError *error) {
     NSLog(@"Handling list folder response on: %@", [NSThread currentThread]);
     if (listFolderResult) {
       NSArray<DBFILESMetadata *> *entries = listFolderResult.entries;

       for (DBFILESMetadata *entry in entries) {
         if ([entry isKindOfClass:[DBFILESFileMetadata class]]) {
           DBFILESFileMetadata *fileMetadata = (DBFILESFileMetadata *)entry;
           NSString *filePath = fileMetadata.pathDisplay;
           NSURL *fileOutputUrl = [outputUrl URLByAppendingPathComponent:fileMetadata.name];
           NSString *fileOutputPath = [fileOutputUrl path];
           NSLog(@"Downloading \"%@\" to \"%@\", filePath, fileOutputPath);
           NSString *downloadTaskKey = [NSString stringWithFormat:@"DownloadTask.%@", [NSUUID UUID].UUIDString];

           [self.shouldContinueLock lock];

           if (!_shouldContinue) {
             NSLog(@"No longer continuing...");
             [self.shouldContinueLock unlock];
             return;
           }

           DBDownloadUrlTask *downloadTask = [self downloadFile:filePath fileOutputUrl:fileOutputUrl downloadTaskKey:downloadTaskKey];
           [self.downloadUrlTasks setObject:downloadTask forKey:downloadTaskKey];
           [self.shouldContinueLock unlock];
         } 
         else if ([entry isKindOfClass:[DBFILESFolderMetadata class]]) {
           DBFILESFolderMetadata *folderMetadata = (DBFILESFolderMetadata *)entry;
           NSURL *directoryOutputUrl = [outputUrl URLByAppendingPathComponent:folderMetadata.pathDisplay];
           NSString *directoryOutputPath = [directoryOutputUrl path];

           if (![_fileManager fileExistsAtPath:directoryOutputPath]) {
             NSError *error;
             [_fileManager createDirectoryAtPath:directoryOutputPath withIntermediateDirectories:@(YES) attributes:nil error:&error];
             if (error) {
               NSLog(@"Error creating directory: %@", error);
             }
           }

           [self downloadFolderHelper:[NSString stringWithFormat:@"%@/%@", inputPath, folderMetadata.name] outputUrl:directoryOutputUrl];
         } else if ([entry isKindOfClass:[DBFILESDeletedMetadata class]]) {
           continue;
         }
       }
       [self.tasksLock lock];
       [_downloadUrlTasks removeObjectForKey:listFolderTaskKey];
       [self.tasksLock unlock];
     } else {
       NSLog(@"Error listing folder \"%@\":", inputPath);
       if (routeError) {
         NSLog(@"RouteError: %@", routeError);
       }
       NSLog(@"Error: %@", error);
     }
   }]; 

  return listFolderTask;
}

-(DBDownloadUrlTask *)downloadFile:(NSString *)filePath fileOutputUrl:(NSURL *)fileOutputUrl downloadTaskKey:(NSString *)downloadTaskKey {
  DBDownloadUrlTask *downloadTask = [[_client.filesRoutes downloadUrl:filePath overwrite:@(YES) destination:fileOutputUrl]
   response:_responseQueue response:^(DBFILESFileMetadata *downloadResult, DBFILESDownloadError *routeError, DBError *error, NSURL *destination) {
     NSLog(@"Handling download response on: %@", [NSThread currentThread]);
     if (downloadResult) {
       NSLog(@"Successfully downloaded \"%@\" to \"%@\", downloadResult.pathDisplay, [destination path]);
       [self.tasksLock lock];
       [self.downloadUrlTasks removeObjectForKey:downloadTaskKey];
       [self.tasksLock unlock];
     } else {
       NSLog(@"Error downloading \"%@\" to \"%@\", filePath, [fileOutputUrl path]);
       if (routeError) {
         NSLog(@"RouteError: %@", routeError);
       }
       NSLog(@"Error: %@", error);
     }
   }];

  return downloadTask;
}

-(void)cancelDownload {
  [self.shouldContinueLock lock];
  self.shouldContinue = NO;
  [self.shouldContinueLock unlock];

  [self.tasksLock lock];
  [self cancelAndClearTasks];
  [self.tasksLock unlock];
}

 

- (void)cancelAndClearTasks {
  for (NSString *key in _rpcTasks) {
    DBRpcTask *task = _rpcTasks[key];
    [task cancel];
    NSLog(@"Canceled task: %@", @(task.task.taskIdentifier));
  }

  for (NSString *key in _downloadUrlTasks) {
    DBDownloadUrlTask *task = _downloadUrlTasks[key];
    [task cancel];
    NSLog(@"Canceled task: %@", @(task.task.taskIdentifier));
  }

  [_rpcTasks removeAllObjects];
  [_downloadUrlTasks removeAllObjects];
}