Presenting view controllers on detached view controllers is discouraged & lt; CallViewController: 0x14676e240 & gt;., discouraged

Presenting view controllers on detached view controllers is discouraged <CallViewController: 0x14676e240>., discouraged

When I optimized the app today, I found that the program had this warning:"

Presenting view controllers on detached view controllers is discouraged <CallViewController: 0x14676e240>.

"

First of all, this problem occurs when a prompt box is displayed when no network is determined.

When querying information on the Internet, it is said that the current controller has present a view, and then present a view, this error will occur. However, in my project, there is no second present in the current page, so there are no more present views. I solve the problem as follows:

Put the present operation in the thread for execution.

 

However, although the problem has been solved, I do not know why it is caused. It is also true that the present operation is not put in the thread, because there was no present operation before, I am very entangled. I hope I can solve this problem and see my summary!