In Xcode Document App: Why would init method of MyDocument be called twice?

I followed Chapter 8 of Hillegass to implement the RaiseMan application there. Then I decided to follow the same process to impleme开发者_StackOverflow社区nt the code for an exercise in a Cocoa programming class that I am taking, but I got the following very cryptic error message after building and running.

Cannot create BOOL from object <_NSControllerObjectProxy: 0x100460e30> of class _NSControllerObjectProxy

I have no idea what this error message means. Doing a Google search brought up some hits, but their remedies seemed to be to do things that I was already doing.

I stared at all the connections and assignments that I made in Interface Builder and nothing looks obviously wrong.

So I went into the debugger and set a breakpoint inside the init method of the MyDocument class and it is being called twice. How could that happen? What should I be looking for that would make the init method be called twice? The stack trace shows that init is called by system functions that we did not write ourselves.

For comparison, I went back to the project that follows Chapter 8 of Hillegass and set a breakpoint inside the init method of the MyDocument class, and it is being called once ( which is what one would expect ).

Cannot create BOOL from object <_NSControllerObjectProxy: 0x100460e30> of class _NSControllerObjectProxy

It appears you've bound a BOOL property to a controller, and not specified a model key path. Most probably, you bound one of the Cocoa view classes' built-in bindings, such as enabled or editable.

Look through your nib for views whose enabled or editable you've bound, and make sure they are all bound to the correct model key path.

I just ran into this myself. And then I remembered seeing something odd before, whose significance hadn't struck me at the time. Which is that in my XIB file, there was a "My Document" object, in addition to the "File's Owner" object (which is what actually represents the document in the XIB file). I have no idea how it got there, but I deleted it in IB, recompiled, and presto, [MyDocument init] only gets called once now.