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.
i have some problems with delegates under xcode while programming an application for Mac OS. I want to communicate with mobile phones if they are in the same network via TCP. I have the following server integrated in my project:
https://github.com/tuscland/osc-echo-example/blob/master/TCPServer.m
https://github.com/tuscland/osc-echo-example/blob/master/TCPServer.h
The only thing I changed at the server is that I extended the start-method so that I can specify a special port. Also I changed the TCPServerDelegation in TCPServer.h to #protocol.
Now I want to set the delegate to this class. But then I get the following error:
[MobileSync copyWithZone:]: unrecognized selector sent to instance 0x109e0f950
I tried a lot but I could not found any solution.
Here is my code, some irrelevant functions are taken out:
MobileSync.h
#import <Foundation/Foundation.h>
#import "TCPServer.h"
#interface MobileSync: NSObject <TCPServerDelegation> {
}
-(id)init;
-(void)StartServer:(int)port;
-(void)StopServer;
// Properties
#end
MobileSync.m
#import "MobileSync.h"
#import "TCPServer.h"
#implementation MobileSync {
TCPServer *tcpServer;
// Other variables
}
-(id)init {
self = [super init];
if (self != nil) {
// Fill variables with values
}
return self;
}
-(void)StartServer:(int)port {
tcpServer = [[TCPServer alloc] init];
[tcpServer setDelegate:self] // <<<<<<< This line is broken
NSError *__autoreleasing* error = NULL;
if ([tcpServer start:port error:error]) {
NSLog(#"Server started successfully");
}
}
-(void)StopServer {
if (tcpServer.stop)
NSLog(#"Server stoped successfully");
}
// different sync functions
// tcpServer Delegate function
-(void)TCPServer:(TCPServer *)server didReceiveConnectionFromAddress:(NSData *)addr inputStream:(NSInputStream *)istr outputStream:(NSOutputStream *)ostr {
NSLog(#"Connection received.");
}
TCPServer.h
#import <Foundation/Foundation.h>
#import <CoreServices/CoreServices.h>
NSString * const TCPServerErrorDomain;
typedef enum {
kTCPServerCouldNotBindToIPv4Address = 1,
kTCPServerCouldNotBindToIPv6Address = 2,
kTCPServerNoSocketsAvailable = 3,
} TCPServerErrorCode;
#interface TCPServer : NSObject {
#private
id delegate;
NSString *domain;
NSString *name;
NSString *type;
uint16_t port;
CFSocketRef ipv4socket;
CFsocketRef ipv6socket;
NSNetService *netService;
}
#property (readwrite, copy) id delegate;
#property (readwrite, copy) NSString *domain;
#property (readwrite, copy) NSString *name;
#property (readwrite, copy) NSString *type;
#property (readwrite) uint16_t port;
-(BOOL)start:(int)port error:(NSError **)error;
-(BOOL)stop;
-(void)handleNewConnectionFromAddress:(NSData *)addr inputStream:(NSInputStream *)istr outputStream:(NSOutputStream *)ostr;
#end
#protocol TCPServerDelegation
-(void)TCPServer:(TCPServer *)server didReceiveConnectionFromAddress:(NSData *)addr inputStream:(NSInputStream *)istr outputStream:(NSOutputStream *)ostr;
#end
Can someone help me solving the problem? That would be great
I am trying to write a cocoa touch static library.
To keep it simple I would prefer not to use private variables within my interface file.
The code right now looks like this:
interface file (myView.h):
#interface myView: UIView {
NSTimer * myTimer;
}
#end
implementation file (myView.h)
#implementation myView
#end
This NSTimer pointer is just a private variable so I tried this:
(not working)
interface file (myView.h):
#interface myView: UIView {
}
#end
implementation file (myView.h)
NSTimer * myTimer;
#implementation myView
#end
It seems to work however it turned out that the timer is now a static variable.
Am I doing sth wrong or is there no solution?
You can't define instance variables in your implementation file.
A possible solution is to have a private structure containing the private variables and have one publicly declared private variable pointing to this private structure:
#interface MyView {
void *privateData;
}
Implementation file:
typedef struct {
NSTimer *myTimer;
} PrivateData;
#implementation MyView()
#property (readonly) PrivateData *privateData;
#end
#implementation MyView
- (id) init {
if (self = [super init]) {
privateData = malloc(sizeof(PrivateData));
self.privateData->myTimer = nil; // or something else
}
return self;
}
-(PrivateData *) privateData {
return (PrivateData *) self->privateData;
}
- (void) myMethod {
NSTimer *timer = self.privateData->myTimer;
}
- (void) dealloc {
// release stuff inside PrivateData
free(privateData);
[super dealloc];
}
#end
It's not beautiful, but it works. Maybe there are better solutions.
Just a note; trying to hide iVar's for the sake of security is silly. Don't bother.
For simplicity's sake, though, it has value.
However, a couple of solutions:
(1) If targeting iPhone OS or 64 bit Cocoa, you can #synthesize the ivar:
Foo.h:
#interface Foo:NSObject
#property(readwrite, copy) NSString *publiclyReadwriteNoiVar;
#property(readonly, copy) NSString *publiclyReadonlyPrivatelyReadwriteNoiVar;
#end
Foo.m:
#interface Foo()
#property(readwrite, copy) NSString *privateProperty;
#end
#implementation Foo
#synthesize publiclyReadwriteNoiVar, publiclyReadonlyPrivatelyReadwriteNoiVar, privateProperty;
#end
(2) Use a private subclass kinda like class clusters:
Foo.h:
#interface Foo:NSObject
#end
Foo.m:
#interface RealFoo:Foo
{
.... ivars here ....
}
#end
#implementation RealFoo
#end
#implementation Foo
+ (Foo *) convenienceMethodThatCreatesFoo
{
.... realFoo = [[RealFoo alloc] init]; ....
return realFoo;
}
#end
Depending on the goal of your encapsulation, there's also the #private directive:
Access Modifiers
I came across a library written in Objective C (I only have the header file and the .a binary).
In the header file, it is like this:
#interface MyClass : MySuperClass
{
//nothing here
}
#property (nonatomic, retain) MyObject anObject;
- (void)someMethod;
How can I achieve the same thing? If I try to declare a property without its corresponding ivar inside the interface's {}, the compiler will give me an error. Ultimately, I want to hide the internal structure of my class inside the .a, and just expose the necessary methods to the header file. How do I declare instance variables inside the .m? Categories don't allow me to add ivar, just methods.
For 64 bit applications and iPhone applications (though not in the simulator), property synthesis is also capable of synthesizing the storage for an instance variable.
I.e. this works:
#interface MyClass : MySuperClass
{
//nothing here
}
#property (nonatomic, retain) MyObject *anObject;
#end
#implementation MyClass
#synthesize anObject;
#end
If you compile for 32 bit Mac OS X or the iPhone Simulator, the compiler will give an error.
You may use of the same idiom used in Cocoa classes. If you have a look to NSString class interface in NSString.h you'll see that there is no instance variable declared. Going deeper in GNUstep source code you'll find the trick.
Consider the following code.
MyClass.h
#interface MyClass : NSObject
// Your methods here
- (void) doSomething;
#end
MyClass.m
#interface MyClassImpl : MyClass {
// Your private and hidden instance variables here
}
#end
#implementation MyClass
+ (id) allocWithZone:(NSZone *)zone
{
return NSAllocateObject([MyClassImpl class], 0, zone);
}
// Your methods here
- (void) doSomething {
// This method is considered as pure virtual and cannot be invoked
[self doesNotRecognizeSelector: _cmd];
}
#end
#implementation MyClassImpl
// Your methods here
- (void) doSomething {
// A real implementation of doSomething
}
#end
As you can see, the trick consist in overloading allocWithZone: in your class. This code is invoked by default alloc provided by NSObject, so you don't have to worry about which allocating method should be used (both are valid). In such allocWithZone:, you may use the Foundation function NSAllocateObject() to allocate memory and initialize isa for a MyClassImpl object instead of MyClass. After that, the user is dealing with a MyClassImpl object transparently.
Of course, the real implementation of your class shall be provided by MyClassImpl. The methods for MyClass shall be implemented in a way that considers a message receiving as an error.
You can use a class extension. A class extension is similar as category but without any name. On the Apple documentation they just define private methods but in fact you can also declare your internal variables.
MyClass.h
#class PublicClass;
// Public interface
#interface MyClass : NSObject
#property (nonatomic, retain) PublicClass *publicVar;
#property (nonatomic, retain) PublicClass *publicVarDiffInternal;
- (void)publicMethod;
#end
MyClass.m
#import "PublicClass.h"
#import "InternalClass.h"
// Private interface
#interface MyClass ( /* class extension */ )
{
#private
// Internal variable only used internally
NSInteger defaultSize;
// Internal variable only used internally as private property
InternalClass *internalVar;
#private
// Internal variable exposed as public property
PublicClass *publicVar;
// Internal variable exposed as public property with an other name
PublicClass *myFooVar;
}
#property (nonatomic, retain) InternalClass *internalVar;
- (void)privateMethod;
#end
// Full implementation of MyClass
#implementation MyClass
#synthesize internalVar;
#synthesize publicVar;
#synthesize publicVarDiffInternal = myFooVar
- (void)privateMethod
{
}
- (void)publicMethod
{
}
- (id)init
{
if ((self = [super init]))
{
defaultSize = 512;
self.internalVar = nil;
self.publicVar = nil;
self.publicVarDiffInternal = nil; // initialize myFooVar
}
return self;
}
#end
You can give MyClass.h to anyone with just your public API and public properties. On MyClass.m you declare your member variable private and public, and your private methods, on your class extension.
Like this it's easy to expose public interfaces and hide detail implementation. I used on my project without any troubles.
According to the documentation I've been looking at there is no problem. All you have to do to hide instance variables is to declare them at the start of the #implementation section, inside { ... }. However, I'm a relative newcomer to Objective C and there's a chance I have misunderstood something - I suspect that the language has changed. I have actually tried this system, using XCode 4.2, building code for the iPad, and it seems to work fine.
One of my sources for this idea is the Apple developer documentation at http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/objectivec/Chapters/ocDefiningClasses.html, which gives this pattern:
#implementation ClassName
{
// Instance variable declarations.
}
// Method definitions.
#end
Two possibilities:
It could be taking advantage of the modern runtime's ability to synthesize instance variables, as bbum suggested.
The property might not have an underlying instance variable in that class. Properties do not necessarily have a one-to-one mapping with instance variables.
No you can't. But you can do this if you're not using #property:
.h
#interface X : Y {
struct X_Impl* impl;
}
-(int)getValue;
#end
.m
struct X_Impl {
int value;
};
...
#implementation X
-(void)getValue {
return impl->value * impl->value;
}
#end
How about a macro trick?
Have tested code below
have tested with dylibs - worked fine
have tested subclassing - Warning! will break, I agree this makes the trick not that useful, but still I think it tells some about how ObjC works...
MyClass.h
#interface MyClass : NSObject {
#ifdef MYCLASS_CONTENT
MYCLASS_CONTENT // Nothing revealed here
#endif
}
#property (nonatomic, retain) NSString *name;
#property (nonatomic, assign) int extra;
- (id)initWithString:(NSString*)str;
#end
MyClass.m
// Define the required Class content here before the #import "MyClass.h"
#define MYCLASS_CONTENT \
NSString *_name; \
int _extra; \
int _hiddenThing;
#import "MyClass.h"
#implementation MyClass
#synthesize name=_name;
#synthesize extra=_extra;
- (id)initWithString:(NSString*)str
{
self = [super init];
if (self) {
self.name = str;
self.extra = 17;
_hiddenThing = 19;
}
return self;
}
- (void)dealloc
{
[_name release];
[super dealloc];
}
#end
DON'T do this, but I feel it should be noted that the runtime has the ability to add ivars whenever you want with class_addIvar
I was able to do the following in my library:
myLib.h:
#interface MyClass : SomeSuperClass <SomeProtocol> {
// Nothing in here
}
- (void)someMethods;
#end
myLib.m
#interface MyClass ()
SomeClass *someVars;
#property (nonatomic, retain) SomeClass *someVars;
#end
#implementation MyClass
#synthesize someVar;
- (void)someMethods {
}
#end
The protocol is optional of course. I believe this also makes all your instance variables private though I'm not 100% certain. For me it's just an interface to my static library so it doesn't really matter.
Anyway, I hope this helps you out. To anyone else reading this, do let me know if this is bad in general or has any unforeseen consequences. I'm pretty new to Obj-C myself so I could always use the advice of the experienced.
I don't think the following code written in another answer is working as expected.
The "SomeClass *someVars" defined in the extension class is not an instance variable of MyClass. I think it is a C global variable. If you synthesize someVars, you will get compile error. And self.someVars won't work either.
myLib.h
#interface MyClass : SomeSuperClass <SomeProtocol> {
// Nothing in here
}
- (void)someMethods;
#end
myLib.m
#interface MyClass ()
SomeClass *someVars;
#property (nonatomic, retain) SomeClass *someVars;
#end
#implementation MyClass
#synthesize someVar;
- (void)someMethods {
}
#end