Question

I am trying to get a OS X app I built using Xcode 4.4 on Mountain Lion to work on Lion as well.

Setting the OS X Deployment Target to 10.7 doesn’t help. The app still won’t run on Lion. (The app won’t open, clicking on it does nothing.)

I tried setting the base SDK to 10.7, but I get a lot of errors, because I am using NSArray and NSDictionary literals, subscripting as well as default synthesis of @propertys all over the place.

According to the Objective-C Feature Availability Index these features should work on Lion.

What could the problem be?

Answer 1

NSWindow doesn’t support weak references in Lion. From the “Transitioning to ARC Release Notes”:

Which classes don’t support weak references?

You cannot currently create weak references to instances of the
following classes:

NSATSTypesetter, NSColorSpace, NSFont, NSMenuView, NSParagraphStyle,
NSSimpleHorizontalTypesetter, and NSTextView.

Note: In addition, in OS X v10.7, you cannot create weak references to
instances of NSFontManager, NSFontPanel, NSImage, NSTableCellView,
NSViewController, NSWindow, and NSWindowController. In addition, in OS
X v10.7 no classes in the AV Foundation framework support weak
references. For declared properties, you should use assign instead of
weak; for variables you should use __unsafe_unretained instead of
__weak.

In addition, you cannot create weak references from instances of
NSHashTable, NSMapTable, or NSPointerArray under ARC.

So yes, you should use assign instead when compiling for Lion. (reference)