initWithData: expected struct NSData * warning - objective-c

Question

I am getting a strange warning with my initWithData: method:
warning: incompatible Objective-C
types 'struct NSDictionary *',
expected 'struct NSData *' when
passing argument 1 of 'initWithData:'
from distinct Objective-C type
in TRDevice.h:
#interface TRDevice : NSObject
{
NSString *name;
}
#property (nonatomic, copy) NSString *name;
-(id)initWithData:(NSDictionary *)inData;
#end
in TRDevice.m:
- (id)initWithData:(NSDictionary *)inData
{
if ((self = [super init]))
{
self.name = [inData valueForKey:TRDeviceNameKey];
}
return self;
}
And where I try to instantiate the above object:
NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
NSArray *dataArray = [prefs arrayForKey:TRDevicesKey];
for (NSDictionary *data in dataArray)
{
TRDevice *device = [[TRDevice alloc] initWithData:data];
[self.devices addObject:device];
[device release];
}
This warning goes away if I 1) rename the init method to something else such as initWithDictionary:. or 2) if I pass in nil to initWithData:.
AFAIK NSObject implements no initWithData: method so I am not overriding it either. I have no clue why I'm getting this warning.

Answer 1

+alloc does not return NSObject, it returns id. that's the proper declaration. the type is (from the compiler's perspective) erased when it's returned via + (id)alloc.
most uses of initWithData: take NSData as their first argument. this is part of the reason objc 'reads so well' and is descriptive.
anyways... personally, i'd just rename it to initWithDictionary: for clarity, convention, and to avoid the warning.
another option is to simply declare your initializer to include the type:
- (id)initTRDeviceWithData:(NSDictionary *)data;
this is detailed enough that it is not likely to conflict with other classes in the translation.
or you can declare a convenience constructor:
+ (TRDevice *)newTRDeviceWithData:(NSDictionary *)data;
or a variant for an autoreleased type:
+ (TRDevice *)trDeviceWithData:(NSDictionary *)data; // eww...