UINavigationItem在几秒钟后出现

Question

我创建了一个带有Menu-Structure的应用程序，并希望在初始化第一个ViewController之前有一个DownloadViewController。

因此我在DownloadViewController中编码：

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];

呈现FirstViewController，所有功能仍然存在。但是UINavigationBar中的菜单图标在几秒钟后首先显示。有人可以帮帮我吗？

屏幕截图：View出现后的NavigationBar： 等待 20秒后：

Answer 1

这不是答案，只是提案

我写这里正确格式化评论，尝试改变：

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];