I have an NSInteger in my class like so
In @interface:
NSInteger currentRow;
@property (assign) NSInteger currentRow;
In @implementation:
@synthesize currentRow;
Doing [self setCurrentRow:0]
seems to work fine, but using [self currentRow]
just returns null for some reason, not sure why. When using breakpoints I can see that the value for currentRow
is 0
so it has set fine, but I can't get the value back.
In Objective-C, it's important that you distinguish between objects and primitive types.
An object is always stored as a pointer, which is the object's location in memory. A pointer is just a number. With NSLog
, you can use %p
to see this value. You can display it in the debugger too, like this: print myObject
. A pointer is displayed as a hexadecimal number, with a 0x
prefix. nil
is essentially location zero (0x0000
). When you allocate any kind of object, you'll get a pointer which isn't zero. When you assign an object to a variable, you are simply copying the memory address, not duplicating the object. With NSLog
, you can use %@
to print out an object's description
. In the debugger, like this: print-object myObject
.
Primitive types like NSInteger
aren't objects. Instead of storing a pointer, usually you just store the value. When you assign an NSInteger
variable, you make a copy of the value. You can see the value in the debugger using print
. Or like this: NSLog("%ld", (long)currentRow)
. When you assign a primitive, you copy its value. Don't use %@
or print-object
with primitives — they expect objects.
(I say "usually you just store the value," because you can make pointers to primitive types, too. In situations like yours however it's not necessary.)
[self currentRow]
returns 0, just like you set it. (Furthermore, because Objective-C guarantees initialization of instance variables, it'll return 0 even if you don't set it.)
The problem is that you're expecting a pointer to an object. How you fix your code depends on how you're using it:
print-object currentRow
, change it to print currentRow
.NSLog("%@", currentRow)
, change it to NSLog(%"ld", (long)currentRow)
.currentRow
somewhere else, where an object is required, change your instance variable and property types to NSNumber *
, an object type. Set it with [self setCurrentRow:[NSNumber numberWithInt:0]]
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