I have this code (modified from a tutorial I am following):
#import <Foundation/Foundation.h>
#class Car;
#class Person;
#interface Person: NSObject
#property Car* owningCar;
#end
#implementation Person:NSObject
-(void)dealloc {
NSLog(#"Person is gone");
}
#end
#interface Car:NSObject
#property Person* owner;
#end
#implementation Car:NSObject
-(void)dealloc {
NSLog(#"Car is gone");
}
#end
void testRefCycle () {
Person* me = [[Person alloc] init];
Car* civic = [[Car alloc] init];
me.owningCar = civic;
civic.owner = me;
}
int main(int argc, const char * argv[]) {
#autoreleasepool {
testRefCycle();
}
return 0;
}
I opened up Profiler Leaks, and ran it, expecting to get Leaks, but nothing shows up. Why is there no leak if this creates a reference cycle?
When I ran the project, there is also no output. Why is there no output if there is no leaks?
There is a leak, which is why there is no output — your dealloc methods never run.
But the leak detector never has a chance to detect it, because your program comes to an end in a millionth of a second. You do not have any persistent state over the longer term, which is what is needed for something to count as a leak.
If you ran testRefCycle in an app, for example, where the app itself persists over time, you would see the leak reported. But you are not going to see it in a one-line command-line program without a run loop, which is what you've got.
Related
I am learning Objective-C inheritance and my program is getting lost in a recursive loop and won't come out. It gets hung up when calling a getter function.
I am using XCode version: Version 6.2 (6C101)
My program is given below
Vehicle.h
#ifndef exercise_2_Vehicle_h
#define exercise_2_Vehicle_h
#import <Foundation/Foundation.h>
#interface Vehicle : NSObject
#property float speed;
-(void) start;
-(void) stop;
-(void) park;
#end
#endif
Vehicle.m
#import "Vehicle.h"
#implementation Vehicle
-(void) setSpeed:(float)speed {
self.speed = speed;
}
-(float) speed {
return self.speed;
}
-(void) start {
NSLog(#"Starting the vehicle");
}
-(void) stop {
NSLog(#"Stopping the vehicle");
}
-(void) park {
NSLog(#"Parking the vehicle");
}
#end
Car.h
#ifndef exercise_2_Car_h
#define exercise_2_Car_h
#import "Vehicle.h"
#interface Car : Vehicle
#property (nonatomic) NSString* make;
-(Car*) initMake: (NSString*) make;
-(NSString*) make;
#end
#endif
Car.m
#import "Car.h"
#implementation Car
-(Car*) initMake:(NSString *)make {
self = [super init];
if (self) {
self.make = make;
}
return self;
}
-(NSString*) make {
return self.make;
}
#end
main.m
#import <Foundation/Foundation.h>
#import "Car.h"
#import "Vehicle.h"
int main(int argc, const char * argv[]) {
#autoreleasepool {
// insert code here...
Car* car = [[[Car alloc] init] initMake: #"Camry"];
//[car setSpeed:45];
NSLog(#"The model initialized is ");
[car make];
// [car speed];
}
return 0;
}
The issue you have is caused by creating the property for speed:
#property float speed;
and overriding setSpeed: method.
When you create #property compiler adds two methods for you, in your example setSpeed and speed.
This command:
self.speed = speed;
is equal to:
[self setSpeed: speed];
and inside setSpeed you have this command again which cause the loop. In your example you can remove both methods (setSpeed and speed) because compiler will add it for you. If you need it because you want to do some customisation you should use _speed instead self.speed.
_speed is backed variable added by compiler when using #property.
Change your method to:
-(void) setSpeed:(float)speed {
_speed = speed;
}
to remove the infinite loop.
In the
- (NSString*)make;
use
return _make
instead. The same with the speed.
If you return "self.x" in a getter method, then it's going to try and call the method again because you're requesting it on self. XCode will automatically convert the properties into variables that can be accessed with an '_' character, so you don't need to do any extra work.
You could also ignore our advice and remove both the "speed" and "make" getter methods you have made, because XCode automagically creates them for you.
So I am quite new on OC programming, I come from Front-end background (i.e. HTML/CSS/JavaScript ...), so I understand basic concepts of programming :)
Basically I created a console application, with a simple FooClass.
FooClass.h
#import <Foundation/Foundation.h>
#interface FooClass : NSObject
#property (strong, nonatomic) NSString *username;
- (NSString *) username;
- (void) setUsername:(NSString *)username;
#end
FooClass.m
#import "FooClass.h"
#implementation FooClass
#synthesize username = _username;
- (instancetype) init
{
self = [super init];
if (self) {
}
return self;
}
- (NSString *) username
{
return _username;
}
- (void) setUsername:(NSString *)username
{
_username = username;
}
#end
And in the main.m file, where the app bootstraps.
#import <Foundation/Foundation.h>
#include "FooClass.h"
int main(int argc, const char * argv[])
{
#autoreleasepool {
// insert code here...
NSLog(#"Hello, World!");
FooClass *foo = [[FooClass alloc] init];
foo.username = #"a";
}
return 0;
}
XCode tells me that it cannot find property username on object of type FooClass. And I don't really have idea about it. Any one could help?
I am a bit late in posting the answer. Here are few things that you should consider.
Since you have a property username. You are not required to create methods for setters and getters. The compiler will create them for you. Simply remove the two statements.
No need to synthesize in .m as well.
Instead of #include use #import. import takes only one copy even if you try to add the file(s) directly or indirectly from other files as compared to include.
Okay. Tough to find the best starting point, here. The error XCode (4.3.2) in Lion is kicking back to me is:
Redefinition of 'a' with a different type
The author says when we declare this line (near the bottom of this page, in main)...
OwnedAppliance *a = [[OwnedAppliance alloc] init];
...that it should run fine. It doesn't. It kicks back the error above. I understand that, because OwnedAppliance has no init method in its implementation, the compiler will go up the hierarchy to OwnedAppliance's superclass, which is Appliance, and search for an init method there. It finds the overridden init, which contains only the following line...
[self initWithProductName:#"Unknown"];
...and runs that. Understood.
Ugh. Sorry, guys. I just tried to explain what I think might be happening. It took a dozen lines and I'd just scratched the surface. Rather than bore you with what I think is happening, I'll just ask:
What's going on with this code? Where does the initialization "path", for lack of a better term, end? Where does the redefinition (the error) occur?
/******************** Appliance.h ********************/
#import <Foundation/Foundation.h>
#interface Appliance : NSObject
{
NSString *productName;
int voltage;
}
#property (copy) NSString *productName;
#property int voltage;
-(id)init;
// Designated initializer
-(id)initWithProductName:(NSString *)pn;
...
#end
/******************** Appliance.m ********************/
#import "Appliance.h"
#implementation Appliance
#synthesize productName, voltage;
-(id)init
{
return [self initWithProductName:#"Unknown"];
}
-(id)initWithProductName:(NSString *)pn
{
self = [super init];
if (self) {
[self setProductName: pn];
[self setVoltage: 120];
}
return self;
...
#end
/******************** OwnedAppliance.h ********************/
#import "Appliance.h"
#interface OwnedAppliance : Appliance
{
NSMutableSet *ownerNames;
}
// Designated initializer
-(id)initWithProductName:(NSString *)pn
firstOwnerName:(NSString *)n;
...
#end
/******************** OwnedAppliance.m ********************/
#import "OwnedAppliance.h"
#implementation OwnedAppliance
-(id)initWithProductName:(NSString *)pn
firstOwnerName:(NSString *)n
{
self = [super initWithProductName:pn];
if (self) {
ownerNames = [[NSMutableSet alloc] init];
if (n) {
[ownerNames addObject:n];
}
}
return self;
}
-(id)initWithProductName:(NSString *)pn
{
return [self initWithProductName:pn
firstOwnerName:nil];
}
...
#end
/******************** main.m ********************/
#import <Foundation/Foundation.h>
#import "Appliance.h"
#import "OwnedAppliance.h"
int main(int argc, const char * argv[])
{
#autoreleasepool {
// Previously omitted problematic code:
Appliance *a = [[Appliance alloc] init];
NSLog(#"a is %#", a);
[a setProductName:#"Washing Machine"];
[a setVoltage:240];
NSLog(#"a is %#", a);
// The following line is where the error occurs:
OwnedAppliance *a = [[OwnedAppliance alloc] init];
...
}
return 0;
}
I've thought a lot about this question and how to ask it. I don't think it's a terribly dumb one. :) But my brain is fried from 9 hours of studying this stuff, so I apologize if this is a totally obvious question. TIA
EDIT: main() now contains the code that was actually causing the error. Thanks to Jacques for being good enough to catch it despite the omission.
The compiler's actually telling you that the variable itself, a, has been declared twice; the error has nothing to do with the assignment. Somehwhere else, in scope, you have another variable named a, which has a different type than OwnedAppliance *. Change the name(s) of one (or both) and the error will go away.
I want to have an ivar of type Class, and to keep the pointer around after it is passed in. But no matter what I do, arc will not let me do that. For instance, if I declare
#property (nonatomic, strong) Class myClass;
the compiler decides that myClass should be unsafe_unretained. And if I try this:
-(id) initWithClass: (Class) passedInClass {
if ((self = [super init])) {
self.myClass = passedInClass;
}
return self;
}
what happens is that even if the class is non-nil in the calling code, it is nil within the init method.
Short of turning off arc, is there any way to get around this?
EDIT: This question is just wrong. It does work. See the accepted answer.
Works as advertised with Xcode 4.3.2 targeting 10.7 and 5.1:
#interface MOYNObject : NSObject
#property (nonatomic, strong, readwrite) Class myClass;
#end
#implementation MOYNObject
#synthesize myClass;
- (id)initWithClass:(id)pClass
{
self = [super init];
if (self != nil)
self.myClass = pClass;
assert(self.myClass);
CFShow((__bridge const void*)self.myClass);
return self;
}
#end
int main(int argc, const char* argv[]) {
#autoreleasepool {
MOYNObject * o = [[MOYNObject alloc] initWithClass:[NSString class]];
// ...
}
return 0;
}
Are you ahead of or behind 4.3.2?
I am working on an example from a book that I got and it doesnt seem to be working I am getting the warning Incomplete implementation. When I run the program I get an error singal "EXC_BAD_ACCESS". The warning is in the .m file at the line return [NSString stringWithFormat:#"Name:... Does anyone know what I am doing wrong?
my .m file
#import "RadioStation.h"
#implementation RadioStation
+ (double)minAMFrequency {
return 520.0;
}
+ (double)maxAMFrequency {
return 1610.0;
}
+ (double)minFMFrequency {
return 88.3;
}
+ (double)maxFMFrequency {
return 107.9;
}
- (id)initWithName:(NSString *)newName atFrequency:(double)newFreq atBand:(char)newBand {
self = [super init];
if (self != nil) {
name = [newName retain];
frequency = newFreq;
band = newBand;
}
return self;
}
- (NSString *)description {
return [NSString stringWithFormat:#"Name: %#, Frequency: %.1f Band: %#", name, frequency, band];
}
- (void)dealloc {
[name release];
[super dealloc];
}
#end
My .h file
#import <Cocoa/Cocoa.h>
#interface RadioStation : NSObject {
NSString *name;
double frequency;
char band;
}
+ (double)minAMFrequency;
+ (double)maxAMFrequency;
+ (double)minFMFrequency;
+ (double)maxFMFrequency;
-(id)initWithName:(NSString*)name
atFrequency:(double)freq
atBand:(char)ban;
-(NSString *)name;
-(void)setName:(NSString *)newName;
-(double)frequency;
-(void)setFrequency:(double)newFrequency;
-(char)band;
-(void)setBand:(char)newBand;
#end
radiosimulation.m file:
int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
// insert code here...
NSMutableDictionary* stations = [[NSMutableDictionary alloc] init];
RadioStation* newStation;
newStation = [[RadioStation alloc] initWithName:#"Star 94"
atFrequency:94.1
atBand:'F'];
[stations setObject:newStation forKey:#"WSTR"];
[newStation release];
NSLog(#"%#", [stations objectForKey:#"WSTR"]);
newStation = [[RadioStation alloc] initWithName:#"Rocky 99"
atFrequency:94.1
atBand:'F'];
[stations setObject:newStation forKey:#"WKFR"];
[newStation release];
NSLog(#"%#", [stations objectForKey:#"WKFR"]);
[stations release];
[pool drain];
return 0;
You are declaring the following property accessor/mutators (getter/setters) but are not implementing them in your .m file.
-(NSString *)name;
-(void)setName:(NSString *)newName;
-(double)frequency;
-(void)setFrequency:(double)newFrequency;
-(char)band;
-(void)setBand:(char)newBand;
You need to implement all 6 of these methods in the .m file if you want to remove the warning about incomplete implementation.
You are effectively saying in the .h file that this is what your object is going to do, then not doing it in the .m. It won't generate an error, as objective-c messaging means that the message will be handed up to NSObject to deal with, which will also not have any matching implementation, and the messages will just be silently ignored. I don't like the way that this is only shown as a warning - but there you go.
That said, I wouldn't create the properties like this (there are neater ways of doing this in objective-c using #property), I would remove those method declarations in the .h and replace them with:
#property (nonatomic, retain) NSString *name;
#property (nonatomic, assign) double frequency;
#property (nonatomic, assign) char band;
These property declarations go in the same place as method declarations.
and then add the following to the .m file:
#synthesize name;
#synthesize frequency;
#synthesize band;
This will avoid having to write all that boilerplate accessor/mutator code that you are currently missing. Again, these go in the same region of the code as method implementations. Effectively the compiler is going to create name and setName methods automatically.
This code is untested - but should point you in the right direction for tidying up the incomplete implementation. It may fix your access error too - but that may require more detailed look at a stack trace.
Another point I'm not sure the code as written even needs to use get/set methods or properties. You might try removing the method declarations from the .h and see if it works. It seems that all the accesses to name, frequency and band are all from within the object.