重新加载tableView时出现奇怪的错误

Question

I have a very general table view.

when it is refreshed, it will go to fetch list of objects from Parse. Analyze these data in a dispatch_async queue, then refresh table view. Most time, it has no problem, but some time reloadData() crash

Is it crashes because the tableView is reloading data when I call it? (when the tableview is init, reloadData may be called automatically) How to avoid this error? ( there is no error message in console )

EDIT: I tries to put ? , but does not work

Answer 1

This happens when your tableView (or whatever object you're sending the message to) is nil. So sometime before your async call dispatched this on the main queue, your tableView got dealloacted.

Check this link out for some info:

http://www.touch-code-magazine.com/how-to-debug-exc_bad_access/

Answer 2

You will get EXC_BAD_ACCESS error mostly in the following scenarios:

You are trying to access an object that is not initialized.

You are trying to access an object that no longer exists. Either it's being released or it's nil. In ARC mode, make sure you take ownership of the object that you want to use. You are passing an message to an object that the object doesn't understand.

It can also happen for bad typecast. Like the lines below where I am trying to access an int with %@ in stead of %d.

 int myAwesomeInt = 9;
 NSLog(@"%@", myAwesomeInt);

How to debug:

Identify what you did that caused the crash. Did it crash while view of a particular view controller didLoad or in a delegate method or on a particular action. That will often help to find the object that is casuing the error.

(In your case look at what specifically happens when you are reloading the table. Do a stack trace line by line and see what your code is doing during a reload)

Most of the time “NSZombies” can help to identify the dead object. You can enable NSZombies by editing your scheme Product -> Edit Scheme -> Diagnostics.

If you still don't find the root cause then always go backwards from child view controller to parent view controller to see what object needs to be retained or what message needs to be passed properly. Look into Static Analyzer and Instruments for advanced debugging.

Credit: The Basic Troubleshooting guide

Hope this helps. Good Luck