Open File Dialog crashes in Swift

Question

I would like to use the open file dialogs from NSFilemanager but my code crashes sometimes and sometimes works and I do not know why. Sometimes it works 100%, sometimes the

Answer 1

Most of the User Interface (UI) Calls are not Thread-Save, that means that they only work without crash and unusual behaviour in the main-thread.

This is the problem with NSOpenPanel Calls, too. When calling from the main-thread everything is OK.