How to properly close NSOpenPanel?

Question

Cocoa

I need to load a list of files from a directory. To do this, I use the beginSheetModalForWindow:completionHandler: method, then select a directory and click OK. In my case, after OK, the addToList: method is called, which conditionally loads the files and the NSOpenPanel does not close until the addToList: method finishes its work. If you need to call a sheet with an NSProgressIndicator that shows the status of the file upload, then it pops up on top of the NSOpenPanel. I do not like this variety of sheets and I solved this issue by calling the close method for NSOpenPanel before calling the sheet with progress.
For example:

NSOpenPanel *panel = [NSOpenPanel openPanel];
[panel beginSheetModalForWindow:window completionHandler:^(NSInteger result) {
        if (result == NSOKButton) {

            [panel close]; //<--- Закрываю sheet c NSOpenPanel

            [NSApp beginSheet:progressSheet modalForWindow:window modalDelegate:nil 
               didEndSelector:nil contextInfo:nil]; //<--- Открываю sheet c индикатором прогресса

            [self addToList:panel.URL]; // <--- загружаю файлы

            [progressSheet orderOut:self];  //
            [NSApp endSheet:progressSheet]; //<--- Закрываю sheet c индикатором прогресса

        }
     }];

Is my solution with calling [panel close] the right choice. And how do you implement such things?
Thank you all in advance.