几秒钟后出现 UINavigationItem

Question

我创建了一个具有菜单结构的应用程序，并希望在初始化第一个 ViewController 之前进行下载ViewController。

因此我在下载中编码ViewController:

NSURLSessionDataTask *downloadTask = [[NSURLSession sharedSession] dataTaskWithURL:downloadUrl completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {

    //Doing download stuff ... (still working)

    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
    UIViewController *vc = [storyboard instantiateViewControllerWithIdentifier:@"firstViewController"];
    [vc setModalPresentationStyle:UIModalPresentationFullScreen];

    [self presentViewController:vc animated:YES completion:nil];
}];

[downloadTask resume];

第一个ViewController出现了，所有的功能都还在。但是 UINavigationBar 中的菜单图标在几秒钟后首次显示。谁能帮帮我？

截图：View出现后的NavigationBar：在等待将近 20 秒后：

Answer 1

这不是答案，只是建议

我写这里是为了正确格式化评论，尝试更改这里：

NSURLSessionDataTask *downloadTask = [[NSURLSession sharedSession] dataTaskWithURL:downloadUrl completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {

    //Doing download stuff ... (still working)

    dispatch_async(dispatch_get_main_queue()) {
        UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
        UIViewController *vc = [storyboard instantiateViewControllerWithIdentifier:@"firstViewController"];
        [vc setModalPresentationStyle:UIModalPresentationFullScreen];

        [self presentViewController:vc animated:YES completion:nil];
    }
}];

[downloadTask resume];

几秒钟后出现 UINavigationItem

UINavigationItem appearing after a few seconds

objective-c

uinavigationbar

ios