为多个文件下载添加子进度

Question

我在我的项目中使用 AFNetworking 3.0 下载多个文件。我想显示所有文件的单个下载进度。我将每个文件下载的每个子进度添加到父进度中。但它不起作用，应用程序崩溃了。我收到错误 -

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '<DownloadManager: 0x7f92e2f6e130>: An -observeValueForKeyPath:ofObject:change:context: message was received but not handled.
Key path: fractionCompleted

这是我的下载类 -

@interface DownloadManager ()
@property (nonatomic, strong) NSProgress *progress;
@property (nonatomic, strong) Settings *settings;
@property (nonatomic, strong) DocumentDirectory *documentDirectory;
@end

@implementation DownloadManager
- (instancetype)init
{
    self = [super init];
    if (self) {
        self.progress = [NSProgress new];
        [self.progress addObserver:self forKeyPath:@"fractionCompleted" options:NSKeyValueObservingOptionNew context:NULL];
        self.settings = [Settings new];
        self.documentDirectory = [DocumentDirectory new];
    }
    return self;
}
- (void) dealloc {
    [self.progress removeObserver:self forKeyPath:@"fractionCompleted"];
}

//Download the file from remote server in the document directory as Zip format
- (void) downloadCarContents:(NSArray *)urlArray forContent:(NSArray *)contentArray {
    AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
    self.progress.totalUnitCount =  urlArray.count;
    self.progress.completedUnitCount = 0;
    for (NSInteger i = 0; i < urlArray.count; i++) {
        NSString *destinationPath = [self.documentDirectory getDownloadContentPath:contentArray[i]];
        NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:urlArray[i]]];
        NSURLSessionTask *task = [manager downloadTaskWithRequest:request progress:nil destination:^NSURL *(NSURL *targetPath, NSURLResponse *response) {
            return [NSURL fileURLWithPath:destinationPath];
        } completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error) {

        }];
        NSProgress *childProgress = [manager downloadProgressForTask:task];
        [self.progress addChild:childProgress withPendingUnitCount:1];
        NSLog(@"Total downloaded : %f", self.progress.fractionCompleted * 100.0);
        [task resume];
    }
}
@end

Answer 1

你忘了实现observeValueForKeyPath:ofObject:change:context:方法。

- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(id)object
                        change:(NSDictionary<NSString *, id> *)change
                       context:(void *)context {
    if ([keyPath isEqualToString:@"fractionCompleted"]) {
        // process value
    }
}