how to solve unrecognized selector sent to instance?

Answer 1

There is way too little information here to diagnose exactly whats causing this, but one thing is certain. The method you are sending to the object is not defined for that object. Please post the code thats causing the error and the .h and .m files for the simple view you are talking about.

You probably need to set the class of the view controller in IB to LibraryDescripViewController. Double click the LibraryDescripViewController.xib file in xcode and when IB opens, in the identity view of the file's owner set the class to LibraryDescripViewController

Answer 2

You can get more information about where the error is happening by opening your debugger window, clicking on "Show Breakpoints", and setting the following two breakpoints:

[NSException raise]
objc_exception_throw

Now when your app is about to crash, the debugger will usually show you exactly what line of code is causing the problem.

For this reason, it's good practice to have these breakpoints on every app you are developing.

Answer 3

It seems that you are calling "self.libraryDescripViewController = aLib" which is another way of writing [self setLibraryDescripViewController:alib].

The most likely cause of this would be in that you haven't declared the method setLibraryDescripViewController in your class.

Hope this helps.