I'm tearing my hair out over this.. I've no idea what's going wrong.
I've created a very simple Coordinates2D class to store two NSInteger values, as well as a string representation for use with NSLog. I'm running this code in the iOS 4.3 iPad simulator bundled with the latest version of xCode.
For some reason the integer values passed to the initX:Y: constructor gets lost. The code below provides Coordinates2D and some code to print an arbitrary float value in its original form, cast as an int, cast as an NSInteger, and then inside the Coordinates2D object.
You should see, as I do, that the value gets lost inside the Coordinates2D constructor; the 'coords.x' argument in NSLog is printed as a random, large integer indicating its value has been lost in memory.
Can anyone help me see why this happens? I can't see what I'm doing wrong.
Many thanks!
Coordinates2D.h
#import <Foundation/Foundation.h>
#interface Coordinates2D : NSObject {
NSInteger x,y;
NSString *asString;
}
#property (nonatomic) NSInteger x,y;
#property (nonatomic, retain) NSString *asString;
-(void)updateStringRepresentation;
-(id)initX:(NSInteger)x Y:(NSInteger)y;
#end
Coordinates2D.m
#import "Coordinates2D.h"
#implementation Coordinates2D
#synthesize x,y,asString;
-(id)initX:(NSInteger)x_ Y:(NSInteger)y_ {
NSLog(#"coords: %i, %i",x_,y_);
if ((self = [super init])) {
self.x = x_;
self.y = y_;
NSLog(#"Coordinates stored %i as %i",x_,self.x);
[self updateStringRepresentation];
}
return self;
}
/*
-(void)setX:(NSInteger)newX {
x = newX;
[self updateStringRepresentation];
}
-(void)setY:(NSInteger)newY {
y = newY;
[self updateStringRepresentation];
}
*/
-(void)updateStringRepresentation {
self.asString = [NSString stringWithFormat:#"%i,%i",x,y];
}
-(void)dealloc {
[asString release];
[super dealloc];
}
#end
Example of problem:
Coordinates2D *coords = [[Coordinates2D alloc] initX:(NSInteger)(202.566223/200.00) Y:0.0f];
NSLog(#"202.566223/200.00 = %f, as int:%i, as NSInteger:%i, as Coordinates2D:%i",
202.566223/200.00, (int)(202.566223/200.00), (NSInteger)(202.566223/200.00), coords.x);
I read awhile ago that you should never use the property accessor in init methods.
I think you want to change:
#property (nonatomic) NSInteger x,y;
to:
#property (nonatomic, assign) NSInteger x,y;
That should fix the error, as it runs fine when I put it in an xcode project.
Related
I have a simple Answer class that looks like this:
#interface Answer : NSObject {
NSString *_text;
NSNumber *_votes;
}
#property(nonatomic, retain) NSString *text;
#property(nonatomic, retain) NSNumber *votes;
+(id)initFromAnswerData:(NSSet *)data;
-(id)initWithText:(NSString *)answer;
#end
The implementation looks like this:
#import "Answer.h"
#import "AnswerData.h"
#import "AppDelegate.h"
#implementation Answer
#synthesize text = _text;
#synthesize votes = _votes;
-(id)initWithText:(NSString *)answer {
if( (self=[super init])) {
_text = answer;
_votes = 0;
}
return self;
}
#end
If I create an array of Answers in a view controller using the initWithText: method I inevitably have EXC_BAD_ACCESS errors when I take an Answer in the array and try to find it's text value.
However if I initialize a new Answer, set the text value and then add it to the array I don't have this access issue.
So this causes problems down the line:
[arrayOfAnswers addObject:[[Answer alloc] initWithText:#"Hello"]];
But this doesn't:
Answer *newAnswer = [[Answer alloc] initWithText:nil];
newAnswer.text = #"Hello";
[arrayOfAnswers addObject:newAnswer];
Can anyone explain why?
You're using the attribute _text and _votes directly but not their setters.
So, you're not retaining the input parameter answer for the line
_text = answer;
You should either change to
_text = [answer retain];
or
self.text = answer;
Are you retaining the array that you put your Answers into? That would be my guess at what's wrong.
as you see , your
#property(nonatomic, retain) NSString *text; // this property is retain.
so the setter method of this should be- (void) setText:(NSString*)text{
[_text release];
_text = text;
[_text retain];
so when you call newAnswer.text = #"hello" ,it works, newAnswer holds the text.
but in your initWithText, there's no retain symbol, so sucks.
I'm trying to teach myself Objective-C and as an exercise, I'm trying to write an app with one button and one label. When I click on the button, I want to trigger a calculation then see the results in the label. The following code compiles and runs with no errors or warnings but as far as I can tell, the [object method] 'call' doesn't do anything. I've spent hours on this and just don't see what's wrong. Can anyone explain the problem? Thanks.
*** testMethodViewController.h ****
#import <UIKit/UIKit.h>
#import "testBrain.h"
#interface testMethodViewController : UIViewController
{
IBOutlet UILabel *display;
testBrain *model;
}
- (IBAction)cellPressed:(UIButton *)sender;
#end
*** testMethodViewController.m ****
#import "testMethodViewController.h"
#implementation testMethodViewController
- (testBrain *)model
{
if (!model) {model = [[testBrain alloc] init];}
return model;
}
- (IBAction)cellPressed:(UIButton *)sender
{
int x = [model check:3]; //This method call doesn't work. But gets no errors.
NSLog(#"Results from model: %i", x); //Says x = 0, but I expect 6
NSString *xAsString = [NSString stringWithFormat: #"testBrain: %i", x];
display.text = xAsString; //Label is updated and displays: testBrain: 0
} //I expect: testBrain: 6
#end
*** testBrain.h ****
#import <Foundation/Foundation.h>
#interface testBrain : NSObject {}
- (int) check:(int) anInteger;
#end
*** testBrain.m ****
#import "testBrain.h"
#implementation testBrain
- (int) check:(int) anInteger //3 passed as the parameter.
{
int r = anInteger + anInteger;
NSLog(#"inside check %i", r); //Debugging line: doesn't print.
return r;
}
#end
When this code runs:
int x = [model check:3];
model is nil. In Objective-C, messages sent to nil silently do nothing, and return 0. So, as you see, x is 0 and -check: is never called.
Apparently you were expecting this method to be called automatically:
- (testBrain *)model
{
if (!model) {model = [[testBrain alloc] init];}
return model;
}
However, that method will be called only if you do it yourself, by saying [self model] or self.model. So, this line would fix it:
int x = [[self model] check:3];
Try it and see.
Going a little further: It would be clearer to remove the model method entirely, and create the instance variable model when the UIViewController is created. That way, we can guarantee that model is valid anytime any code in the testMethodViewController class runs.
You would do that by overriding UIViewController's designated initializer:
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// Now you can initialize your instance variables
model = [[testBrain alloc] init];
}
return self;
}
With your model method, you are halfway towards Lazy Instantiation, however to properly achieve this, you must always acess the lazily instantiated object through its accessor method. You aren't doing this in your button action, so your messages are going to nil, which is silently ignored.
This is one of the reasons you often see instance variables in objective-c declared with a leading or trailing underscore. If you then typed model anywhere in the rest of your class, it would be a compiler error, forcing you to use the accessor. Typically this is implemented with properties and the synthesize statement:
In your interface:
#property (nonatomic, strong) TestBrain* model;
In your implementation:
#synthesize model = model_;
Your model method would be:
-(TestBrain*)model
{
if (!model_)
model_ = [[TestBrain alloc] init];
return model_;
}
You would then use self.model instead of model throughout the rest of the class.
If you are just starting out, the Stanford iOS course on iTunes U is an excellent resource, a lot of this sort of material is covered.
int x = [model check:3];
This line should be:
int x = [self.model check:3];
you are almost there. You need to use #property and #synthesize in order to complete this. The #synthesize directive will direct the compiler to create the setters and getters for a particular property. The #synthesize directive tells the compiler that variable is a property. Properties allow you to use the dot syntax. i.e. self.model which will automatically the call the getter or setter method, depending on the context.
In your testMethodViewController.h file change it to look like this:
#interface testMethodViewController : UIViewController
{
IBOutlet UILabel *display;
testBrain *model;
}
#property (nonatomic,retain) testBrain *model;
- (IBAction)cellPressed:(UIButton *)sender;
#end
then in the .m implementation you need to use #synthesize after the #implementation. Like this:
#implementation testMethodViewController
#synthesize model; // tells the compiler to synthesize the setter and getter for you
- (testBrain *)model
{
if (!model) {model = [[testBrain alloc] init];}
return model;
}
then in your cellPressed: method, you need to use self.model in order for the getter to be called:
- (IBAction)cellPressed:(UIButton *)sender
{
int x = [self.model check:3]; //This method call doesn't work. But gets no errors.
NSLog(#"Results from model: %i", x); //Says x = 0, but I expect 6
NSString *xAsString = [NSString stringWithFormat: #"testBrain: %i", x];
display.text = xAsString; //Label is updated and displays: testBrain: 0
}
Hope this helps.
I dont see anywhere in the testMethodViewController.h file
IBOutlet UIButton *button;
Also check if u have properly connected all IBOutlet, IBAction & delegate, datasource.
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.
It's the first time I'm trying to use typedef. Admittedly I don't have a very clear idea of what's going on but my understanding was that the values inside typedef get assigned integers starting with 0. I've tried to use them as integers but I get various warnings and errors. One of them is "[NSCFNumber objectForKey:]: unrecognized selector sent to instance". I don't know how to troubleshoot this. I also haven't written dynamic getters/setters much, so my approach might be wrong. Please help.
// MyView.h
typedef enum
{
STYLE_A,
STYLE_B,
STYLE_C,
STYLE_D
} MyShapeStyle;
#interface MyView : UIView
{
MyShapeStyle shapeStyle;
CALayer *myLayer;
MyLayerDelegate *myLayerDelegate;
}
#property (nonatomic) MyShapeStyle shapeStyle;
#property (nonatomic, retain) CALayer *myLayer;
#property (nonatomic, retain) MyLayerDelegate *myLayerDelegate;
#end
// MyView.m
#import "MyView.h"
#implementation MyView
#dynamic shapeStyle;
#synthesize myLayer;
#synthesize myLayerDelegate;
- (id)initWithFrame:(CGRect)frame
{
if ((self = [super initWithFrame:frame]))
{
// Initialization code
MyLayerDelegate *delegate = [[MyLayerDelegate alloc] init];
self.myLayerDelegate = delegate;
CALayer *myLayer = [CALayer layer];
[myLayer setDelegate:delegate];
[self.layer addSublayer:myLayer];
self.myLayer = myLayer;
self.shapeStyle = STYLE_C;
[delegate release];
}
return self;
}
-(MyShapeStyle)shapeStyle
{
return [[self.myLayer valueForKey:#"style"] integerValue];
}
- (void)setShapeStyle:(MyShapeStyle)style
{
[self.myLayer setValue:[NSNumber numberWithInt:style] forKey:#"style"];
}
// MyLayerDelegate.m
-(void)drawLayer:(CALayer *)theLayer inContext:(CGContextRef)theContext
{
int id = [[theLayer valueForKey:#"style"] integerValue];
if( id == STYLE_A )
{
}else if ( id == STYLE_B ){
}
}
There is no reason to use valueForKey: in that code; just get/set the various properties directly.
-(MyShapeStyle)shapeStyle
{
return (MyShapeStyle) self.myLayer.style;
}
There is also no need for the #dynamic in that code. That is only needed if you are going to dynamically generate the methods.
As for why the objectForKey: does-not-respond error, there isn't anything in that code that should trigger that. Could be a retain/release issue or it could be a problem in some other code that you haven't shown.
I have a Class that runs the following method (a getter):
// the interface
#interface MyClass : NSObject{
NSNumber *myFloatValue;
}
- (double)myFloatValue;
- (void)setMyFloatValue:(float)floatInput;
#end
// the implementation
#implementation
- (MyClass *)init{
if (self = [super init]){
myFloatValue = [[NSNumber alloc] initWithFloat:3.14];
}
return self;
}
// I understand that NSNumbers are non-mutable objects and can't be
// used like variables.
// Hence I decided to make make the getter's implementation like this
- (double)myFloatValue{
return [myFloatValue floatValue];
}
- (void)setMyFloatValue:(float)floatInput{
if ([self myFloatValue] != floatInput){
[myFloatValue release];
myFloatValue = [[NSNumber alloc] initWithFloat:floatInput;
}
#end
When I mouse over the myFloatValue object during debugging, it does not contain a value. Instead it says: "out of scope".
I would like to be able to make this work without using #property, using something other than NSNumbers, or other major changes since I just want to understand the concepts first. Most importantly, I would like to know what mistake I've apparently made.
I can see a couple of mistakes:
The line #implementation should read #implementation MyClass
The function setMyFloatValue is missing a closing ] and } —it should read:
- (void)setMyFloatValue:(float)floatInput{
if ([self myFloatValue] != floatInput){
[myFloatValue release];
myFloatValue = [[NSNumber alloc] initWithFloat:floatInput];
}
}
I've just tested it in Xcode and it works for me with these changes.
Why not just set property in interface and synthesize accessors in implementation?
#interface MyClass : NSObject {
float *myFloat
}
#property (assign) float myFloat;
#end
#implementation MyClass
#synthesize myFloat;
#end