I guess this is quite basic, but I am struggling with getting data (in this case a simple string) from a class.
My class is quite simple; it looks like this:
#interface myBook : NSObject {
NSString *titleName;
NSString *titleColour;
}
And then I have all the #property and #synthesise calls. I import this (#import myBook.h) in my viewController, where I want to add books to my library. So I have this set of variables to control my library:
NSMutableArray *myLibrary;
NSUInteger currentBookNumber;
myBook *currentBook;
and:
#property (nonatomic, retain) NSMutableArray *myLibrary;
#property (nonatomic, assign) NSUInteger currentBookNumber;
#property (nonatomic, readonly) NoteBook *currentBook;
I then set up my library like so:
-(void) setupLibrary {
myBook *newBook = [[myBook alloc] init];
newBook.titleName = #"Test";
newBook.titleColour = #"orange";
[myLibrary addObject:newBook];
[myLibrary addObject:newBook];
[myLibrary addObject:newBook];
currentBookNumber = 0;
}
In order to get data from the current book I have the following method:
-(NmyBook *) currentBook {
myBook *thisBk = [self.myLibrary
objectAtIndex:self.currentBookNumber];
return thisBk;
}
Now my problem is that if I want to get data from myLibrary and call this in my viewDidLoad, I will only get nil for the title... where did I go wrong?
- (void)viewDidLoad {
[self setupLibrary];
NSLog(#"TitleName:%#", currentBook.titleName);
Issues I see:
Number 1:
I hope the currentBook method return type is a typo. I'm seeing a -(NmyBook *)... shouldn't that be a - (myBook *)?
Number 2:
You never initialized the currentBook object. Before you call the NSLog, you should go
currentBook = [self currentBook];
Where [self currentBook] calls the currentBook method and sets the returned object as the currentBook object.
Finally, try not having the same names for variables and methods :)
Hope that helps.
You have to use self.currentBook.titleName. currentBook.titleName won't trigger your accessor.
By the way, your setupLibrary is leaking. You'll want to add [newBook release] after the last [myLibrary addObject:newBook] call.
You had called one property currentBook and one method currentBook :
Normally it works but you should call the method getCurrentBook;
and the right to access to a property in his class is to use :
[self.theProperty method];
Use :
newBook.titleName = [NSString stringWithFormat:#"Test"];
newBook.titleColor = [NSString stringWithFormat:#"Orange"];
After you can call :
NSLog(#"TitleName:%#", self.currentBook.titleName);
Related
Let say i have an class named as MyTestClass.h.
Class structure is look like
#interface MyTestClass : NSObject {
NSString *testString;
}
#property (nonatomic, retain)NSString * testString;
#end
.m file
#implementation MyTestClass
#synthesize testString;
-(id) init{
[self setTestString:#""];
return self;
}
-(void)dealloc{
[self.testString release];
testString = nil;
[super dealloc];
}
#end
Now i created an object of MyTestClass and assigned testString twice
MyTestClass * myTestClass = [[MyTestClass alloc] init];
[myTestClass setTestString:#"Hi"];
[myTestClass setTestString:#"Hello"];
Now i think, two times my testStrings memory is leaked!! (one through init() and another one through my first setTestString method)
Am i correct? or will #property (nonatomic, retain) handle/release previous allocated memory?
or ,in this kind of cases ,will i need to override the setTestString() in MyTestClass.m like below code
-(void)setTestString:(NSString *)tempString{
[testString release];
testString = nil;
testString = [tempString retain];
}
Any help on this question is appreciated.
Thanks.
Any help on this question is appreciated.
I'll take this as a licence to make sone observations not necessarily directly related to your question.
Firstly, if you declare a retain property (as you have done) and synthesize it, the automatically generated getters and setters handle memory management correctly for you.
If you manually create setter (which you are allowed to do even with an #synthesize existing), you have to do the memory management yourself. Use either of trojanfoe's examples.
The setter in your question contains a bug in that if testString == tempString i.e. you assign the value of the property to itself, you could end up with assigning a dangling pointer to the property because you effectively release tempString and then retain it.
This is an implementation detail that you an safely ignore, but string literals e.g. #"blah" are compiled into the executable and will never be deallocated no matter how many times they are released. So, with your example, even if the setter did not do correct memory management, there will be no leak.
By the way, the normal pattern for an init method is
-(id) init
{
self = [super init];
if (self != nil)
{
// init stuff
}
return self;
}
or logical equivalent.
You should get into the habit of using it because you need to call the super class's init method and it is allowed to change the value of self, even to nil.
Also, while it is very good practice normally to set the object reference to nil after releasing it, in both cases when you do it, it is unnecessary. the first time, the variable is about to go out of scope and the second time you immediately assign it from some other object.
It's not a leak. Synthesized variable are correctly handled.
A synthesized method is implemented in this way (for a retain keyword)
#property (nonatomic, retain) NSString *string;
//backed by variable NSString *_string;
- (void)setString:(NSString*)newString
{
if (newString != _string) {
[_string release];
_string = [newString retain];
}
}
Of course this is a leak:
- (void)aMethod //of my class with string property
{
NSString *aString = [[NSString alloc] initWithString:#"hello"];
self.string = aString; //retain count of 2
self.string = #"hello2"; //retain count of 1 for aString
//now I don't release aString.... leak
}
If you use the auto-generated setter (in your case, setTestString:, which is also called by self.testString = ...;), the previous value of a retain property is released before being set. So no, there is no leak in the code you posted above.
The synthesized setter method should do the right thing. Here's an example of it's implementation:
- (void)setTestString:(NSString *)tempString
{
[tempString retain];
[testString release];
testString = tempString;
}
or:
- (void)setTestString:(NSString *)tempString
{
if (tempString != testString)
{
[testString release];
[tempString retain];
testString = tempString;
}
}
the dealloc is only called when the instance is destructed.
if you do :
[myTestClass setTestString:#"Hi"];
[myTestClass setTestString:#"Hello"];
in the same block, you're juste calling twice the setter. there is no memory leak.
When you use #synthesize on a property that specifies retain, the setter that's generated will handle the retain/release correctly for multiple assignments. As long as you use self. rather than going directly to the backing variable and do a final release in dealloc you should be fine.
What I am doing is
//ClassB.h
#property (strong, nonatomic) NSString *name;
and
//ClassA.h
#interface ClassA : NSObject
+(ClassA*)methodA:(NSData*)data;
-(id)initWithData:(NSData*)data;
#property (nonatomic, strong) NSMutableArray *arr;
#property (nonatomic, strong) RXMLElement *rxmlRoot;
#end
//ClassA.m
#implementation ClassA
#synthesize arr;
#synthesize rxmlRoot;
+(ClassA*)methodA:(NSData*)data {
return [[ClassA alloc] initWithData:data];
}
-(id)initWithData:(NSData*)data {
self = [super init];
if (self) {
arr = [NSMutableArray array];
rxmlRoot = [RXMLElement elementFromXMLData:data];
/*****edit : just been added to make codes clear*****/
NSString *node = #"players.player";
[rxmlRoot iterate:node with:^(RXMLElement *e){
ClassB *classB = [[[ClassB alloc] init] autorelease];
[classB setName: [e attribute:#"name"]];
// adding ClassB into arr
[arr addObject:classB];
}];
}
return self;
}
#end
So now I am having ClassA object whose arr contains ClassB
Question : later on, when I try to access an particular property of ClassB like
((ClassB*)[classA.arr objectAtIndex:0]).name
and I am getting EXC_BAD_ACCESS at above line..
Please advice me on this issue and how to correct the error. Any comments are welcomed here
Thanks
This line
[arr addObject:ClassB]
makes no sense. Is your intention to put an instance of ClassB into that array, or the class itself (i.e. [ClassB class])? Presumably you must intend to put an instance of ClassB in there, otherwise trying to access its properties later on (e.g. firstName) would make no sense. Also, does your ClassB even have a firstName property, because the piece of ClassB's interface that you show us only mentions a name property.
Update:
Since you are using manual memory management, you need to retain the objects (arr, rxmlRoot) you create in your initializer using convenience constructors, which return autoreleased objects. For example, the code should be
arr = [[NSMutableArray array] retain];
Post your ClassB.m .
Are you making the #synthesize name?
Also make the Alloc for arr.
This line is so wrong:
((ClassB*)[classA.arr objectAtIndex:0]).firstName
Your string is called name , not firstName. It should be :
((ClassB*)[classA.arr objectAtIndex:0]).name
The code in the question has changed substantially, so my previous answer now makes no sense and I have removed it. Given revised code, the first thing to do is to log what's going on.
NSLog(#"classA: %#", classA);
NSLog(#"classA.arr: %#", classA.arr);
((ClassB*)[classA.arr objectAtIndex:0]).name
If it blows up on the first log statement, things are really bad. But then at least you know that classA is pointing to something rotten and you can work back from there.
You can achieve the same thing in the debugger, by setting a break point ahead of the line and inspecting. Given that you are getting an EXC_BAD_ACCESS one of the pointers is pointing to a dodgy object, e.g. one that has been released. It looks as if you are using ARC (because you have strong in your property), which should help manage the memory - but then again, you have an autorelease in there, so maybe not.
I have seen that a few others have had this problem as well.
I'm trying to follow a tutorial online that shows how to create animated pins on a MapView.
I have implemented the code as shown in the tutorial and the project builds fine except I receive this exception:
-[MKPointAnnotation iconN]: unrecognized selector sent to instance
I have a subclass of 'MKPinAnnotationView' and in the .m file I create this method:
- (void)setAnnotation:(id<MKAnnotation>)annotation {
[super setAnnotation:annotation];
//Place *place = [[Place alloc] init];
Place *place = (Place *)annotation;
//The following line is where the program sends "SIGABRT"
icon = [UIImage imageNamed:[NSString stringWithFormat:#"pin_%d.png", [place.iconN intValue]]];
[iconView setImage:icon];
}
Here are a few parts from my "model" which is called Place.h/.m.
Here is where I create the property for 'iconN'.
#property (retain, nonatomic) NSNumber *iconN;
And here I synthesize it:
#synthesize iconN = _iconN;
Any help is greatly appreciated.
EDIT:
Here is the Place.h and Place.m
#import <MapKit/MapKit.h>
#import <CoreLocation/CoreLocation.h>
#interface Place : NSObject <MKAnnotation> {
CLLocationCoordinate2D coordinate;
NSString *title;
}
#property (retain, nonatomic) NSNumber *iconN;
#property (nonatomic, copy) NSString *title;
#property (nonatomic) CLLocationCoordinate2D coordinate;
- (id)initWithLong:(CGFloat)lon Lat:(CGFloat)lat iconNumber:(NSNumber *)iconNumber;
#end
And the Place.m
#import "Place.h"
#implementation Place
#synthesize coordinate;
#synthesize iconN = _iconN;
#synthesize title;
- (id)initWithLong:(CGFloat)lon Lat:(CGFloat)lat iconNumber:(NSNumber *)iconNumber {
self = [super init];
if (self) {
coordinate = CLLocationCoordinate2DMake(lat, lon);
self.iconN = iconNumber;
}
return self;
}
- (NSString *)title {
return [NSString stringWithFormat:#"Bus: %d", [self.iconN intValue]];
}
- (NSString *)subtitle {
return [NSString stringWithFormat:#"bus[%d] from database.", [self.iconN intValue] - 1];
}
#end
You cannot convert a MKAnnotation to a Place just by casting it. This line is wrong.
Place *place = (Place *)annotation;
You should post your Place.h and Place.m files if you're still stuck. You need to either set the iconN property on a new Place object, or create an init method in the Place class that accepts the MKAnnotation object as a parameter and sets it own internal values accordingly.
In the line
Place *place = (Place *)annotation;
has the variable place of annotation variable class (MKPointAnnotation), you are not able to bring the master class variable to a subclass in this way. Instead you'll have to make a constructor for Place from MKPointAnnotation and perform a check in the setAnnotation method that annotation is of MKPointAnnotation.
You are sending the message to the annotation but you seem to have subclasses the annotation view.
Posting as an answer what was originally just a comment:
I'm not familiar with the MapKit, but the thing that sticks out for me in this: -[MKPointAnnotation iconN]: unrecognized selector sent to instance is that the class is MKPointAnnotation. So the annotation you're receiving isn't actually a Place object, it's an MKPointAnnotation object - you can't just cast to Place. I suspect the root of your problem is where you create your annotation object in the first place.
Cocoa newbie here. I am working on an iPhone UITableViewController-based widget that can be used to edit date and text properties in an object set during initiation. Currently, I am attempting to do this with a #selector and NSInvocation as below. Note: the "targetObject" is the object set when the controller is initialized.
- (IBAction)saveDate:(id)sender {
//The selector below would normally be passed in when the controller is initialized
[self setDoneSelector:#selector(setDate:)];
NSMethodSignature * sig = nil;
sig = [[targetObject class] instanceMethodSignatureForSelector:[self doneSelector]];
NSInvocation * myInvocation = nil;
myInvocation = [NSInvocation invocationWithMethodSignature:sig];
[myInvocation setTarget:targetObject];
[myInvocation setSelector:doneSelector];
NSDate * myDate = [datePicker date];
[myInvocation setArgument:&myDate atIndex:2];
NSString * result = nil;
[myInvocation retainArguments];
[myInvocation invoke];
}
This works fine on most objects, but I am running into trouble when passing in a Core Data (NSManagedObject) as the targetObject. The object looks like this:
Transaction.h
#import <CoreData/CoreData.h>
#interface Transaction : NSManagedObject
{
}
#property (nonatomic, retain) NSString * message;
#property (nonatomic, retain) NSDate * date;
#end
Transaction.m
#import "Transaction.h"
#implementation Transaction
#dynamic message;
#dynamic date;
#end
If I set this object in my controller as the targetObject, I can call the "setDate:" method directly without issue.
[targetObject setDate:[datePicker date]];
But when I try to invoke it with the #selector, I get 'Program received signal: "EXC_BAD_ACCESS”.'
I imagine this has something to do with the #dynamic methods used in the NSManagedObject and when they are created, but I don't know enough about that process to know how to or if I can workaround this to get it working. I have tried explicitly creating the "setDate:(NSDate *)aDate" method in the Transaction object, and that works, but I am wondering if I should do that and how it might the NSManagedObject.
Can I access these setter methods with a #selector without explicitly defining them?
Agreed w/ NSD here. You should start by simplifying this code to the much simpler -performSelector:withObject: version:
- (IBAction)saveDate:(id)sender {
[self.targetObject performSelector:self.doneSelector withObject:[self.datePicker date]];
}
If that still has trouble, we can start debugging where the real problem is. NSInvocation is a very fancy object for solving this kind of simple problem.
If you still get the crash, then you'll want to look at the actual stacktrace to see what variable is not being correctly initialized or being over-released.
I'm writing an iPhone app. I have a header file that looks like this:
#interface EditTagsViewController : UITableViewController {
NSMutableArray *allTags;
NSMutableArray *selectedTags;
NSInteger currentFavorite;
}
#property (nonatomic, retain) NSMutableArray *allTags;
#property (nonatomic, retain) NSMutableArray *selectedTags;
#property (nonatomic) NSInteger currentFavorite;
#end
In the implementation file, my viewDidLoad method looks like this:
- (void)viewDidLoad {
NSMutableArray *aTags = [[NSMutableArray alloc] initWithArray:[Tag findAllTags]];
self.allTags = aTags;
[aTags release];
NSMutableArray *sTags = [[NSMutableArray alloc] initWithArray:[Tag findByFavoriteId:currentFavorite]];
self.selectedTags = sTags;
[sTags release];
UIBarButtonItem *add = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:#selector(addNewTag:)];
self.navigationItem.rightBarButtonItem = add;
[add release];
[super viewDidLoad];
}
Here is my dealloc method:
- (void)dealloc {
[allTags release];
[selectedTags release];
[super dealloc];
}
What's confusing to me is that when I run the app both in the simulator and on the device itself, using Instruments (memory leaks), it tells me that this line in my viewDidLoad method is leaking an array:
self.selectedTags = sTags;
It's confusing because I'm using the exact same technique with 2 different variables, and yet no leak is reported with the first one.
I feel like I'm missing something obvious here. Any ideas?
Your code looks correct to me. Is it possible that one of [Tag findAllTags] or [Tag findByFavoriteId:] is leaking? Are you making sure to set self.allTags and self.selectedTags to nil in dealloc?
Be mindful of the difference between saying self.allTags = ... and allTags = .... Because allTags is a property and has the retain attribute, whenever you assign via self.allTags = ..., it implicitly calls the setter method [self setAllTags:...], which invokes retain on the new value and release on the old value (if any). You're doing it correctly in this code sample, but if elsewhere you're assigning straight to allTags (without the self.), you're not releaseing the old value, which may be the source of the leak. Likewise for selectedTags.
Have a look at findByFavoriteId is there a retain there? That is the only difference I can see between the aTags and sTags are used in your example