when i navigate between tabbarItem rapidly, app crashes

I fear the problem is in your overall code structure ; in addition, you are overriding some methods without calling super inside when required.

You would need a thorough review of your code, checking in document all the notes about the API you call.

Did you find out ?

What is the crash log you get. This information is indispensible to analyze the problem.

the problem not occured yet, but before that I faced this problem because in a specific tabbaritem , in viewdidload I request data, and when I navigate to other tabbaritem the requset cancelled, so app crashes.

That means that you should close the request in viewWillDisappear(_:)

my requests are firebase observeSingleEvent and request of loading an image by sd_webImage library, how to cancel them?

I post an isuue about sd_webImage on github, but no one reply yet!

Post the code of the complete class, it will be easier to try and help.