如何在ios的afnetworking 3.0中显示进度条？

#import <AFNetworking/AFNetworking.h>

AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];
manager.responseSerializer = [AFHTTPResponseSerializer serializer];

UIProgressView *progressView = [[UIProgressView alloc] initWithProgressViewStyle:UIProgressViewStyleDefault];
progressView.progress = 0.0;

NSURL *URL = [NSURL URLWithString:@"http://example.com/path/to/resource"];
NSURLRequest *request = [NSURLRequest requestWithURL:URL];

NSURLSessionDownloadTask *downloadTask = [manager downloadTaskWithRequest:request progress:^(NSProgress * _Nonnull downloadProgress) {
    dispatch_async(dispatch_get_main_queue(), ^{
        // 更新进度条的进度
        progressView.progress = downloadProgress.fractionCompleted;
    });
} destination:nil completionHandler:nil];

[downloadTask resume];