So I have a class with a NSInteger in it and now I want to return the NSInteger value. For some kind of reason, the code for that is not working. I have already declared the #property for the NSInteger class.
#property (readwrite, assign, nonatomic) NSInteger numberFun;
- (NSInteger)sampleMethod {
...
return sample.numberFun;
}
The compiler says "Return from pointer without a cast". I'm pretty sure that means that I'm using a C type for an objective-c method. I want to know the work around for this. (Though I don't want it to return a casted NSInteger as a NSNumber).
Thanks
The following code sample compiles fine. I suggest you present a more complete example of your problem so we can figure out what you are doing wrong.
#interface MyObject : NSObject
{ }
#property (readwrite, assign, nonatomic) NSInteger numberFun;
#end
#implementation MyObject
#synthesize numberFun;
#end
#interface MyObject2 : NSObject
{ }
#property (nonatomic, copy) MyObject* sample;
#end
#implementation MyObject2
#synthesize sample;
- (NSInteger)sampleMethod { return sample.numberFun; }
#end
Related
Can I assign 'NSNotFound' to a property of type NSInteger? So here is what I have:
#interfcae MyClass()
#property (nonatomic) NSInteger sectionNumber;
#end
#implementation MyClass
- (id)init
{
[my_switch isOn] ? self.sectionNumber = 0 : self.sectionNumber = NSNotFound;
}
#end
This throws an error saying "Assignment to readonly property". Even if I just try "self.sectionNumber = NSNotFound", I get the same error.
Can I not assign NSNotFound to a property? If not what could be the other options I have?
Your code should be:
- (id)init {
self.sectionNumber = [my_switch isOn] ? 0 : NSNotFound;
}
And Wain makes a good point about this init method. Either rename this to something other than init or make this a proper init method.
Update:
Based on your comment you have the following in the .h:
#property (nonatomic, readonly) NSInteger sectionNumber;
This means in the .m you need:
#property (nonatomic, readwrite) NSInteger sectionNumber;
#implementation Fruit{
-(void) setWeight: (int)a{
weight=a;
}
-(void) setType:t{
Type=t;
}
-(void) setName:n{
name=n;
}
the error is in the 2nd line shown. i tried the show invisible spaces trick and it didnt work.
You've got an open bracket { next to your implementation, delete that and make sure your file ends in #end
Edit: The other problems are
You're writing your setters incorrectly. You need to provide a type like you did for setWeight int, for the type and name.
If you're going to make your own setters it needs to be _type = t, and _name = n
I just wrote this code and it builds without issue:
#interface Fruit : NSObject
#property (nonatomic) int weight;
#property (nonatomic, strong) NSString *type;
#property (nonatomic, strong) NSString *name;
#end
#import "Fruit.h"
#implementation Fruit
-(void) setWeight: (int)a{
_weight=a;
}
-(void) setType:(NSString *)t{
_type=t;
}
-(void) setName:(NSString *)n{
_name=n;
}
#end
You don't need brackets around your #implementation. Instead, you just need to put a #end after it
#implementation Fruit
...
#end
Right before my model class sends the variable stringToDisplay, NSLog shows me that it has a value. But when I try to use it in my ViewController, I just get (null). Any thoughts about what I'm doing wrong?
(The good news is that, while working on this, I had sort of a breakthrough in understanding how models and controllers relate to each other. I'm still a complete newbie, but I don't feel quite as lost as I did.)
Here's what I think is the relevant code:
CalculatorBrain.h
#import <Foundation/Foundation.h>
#interface CalculatorBrain : NSObject
#property (nonatomic) NSMutableString *stringToAdd;
#property (nonatomic,strong) NSString *stringForDisplay;
- (double)performOperation:(NSString *)operation withArray:(NSMutableArray *)particularStackYouNeedToPopOff;
CalculatorBrain.m
#implementation CalculatorBrain
#synthesize stringToAdd = _stringToAdd;
#synthesize stringForDisplay = _stringForDisplay;
#synthesize whatHappenedSinceLastClear = _whatHappenedSinceLastClear;
- (double)performOperation:(NSString *)operation withArray:(NSMutableArray *)particularStackYouNeedToPopOff
{
<long code that I think doesn't matter because this NSLog produces exactly what I want it to:>
NSLog(#"%#",stringForDisplay);
return result;
}
CalculatorViewController.h
#import <UIKit/UIKit.h>
#interface CalculatorViewController : UIViewController
#property (nonatomic) NSArray *arrayOfDictionaries;
#property (nonatomic) NSDictionary *dictionary;
#property (weak, nonatomic) IBOutlet UILabel *variablesUsed;
#property (nonatomic, strong) NSString *operation;
#end
CalculatorViewController.m
#import "CalculatorViewController.h"
#import "CalculatorBrain.h"
#interface CalculatorViewController ()
#property (nonatomic,strong) CalculatorBrain *brain;
#end
#implementation CalculatorViewController
#synthesize display = _display;
#synthesize history = _history;
#synthesize brain = _brain;
#synthesize operation = _operation;
- (IBAction)operationPressed:(UIButton *)sender
{
NSString *otherString=[self.brain stringForDisplay];
if (self.userIsEnteringNumber) [self enterPressed];
NSString *operation = sender.currentTitle;
double result = [self.brain performOperation:operation withArray:[self.brain whatHappenedSinceLastClear]];
self.display.text = [NSString stringWithFormat:#"%g",result];
self.history.text = otherString;
NSLog(#"%#",otherString);
}
And the NSLog in that last line of code give me (null).
Any thoughts?
Maybe I'm missing something but your property is declared in the class extension of CalculatorBrain so nobody outside CalculatorBrain.m knows about this property.
So if you want to expose this property to other objects, you will have to declare it in CalculatorBrain.h instead.
Oh - your declaration of the property whatHappenedSinceLastClear isn't exposed to other classes that import CalculatorBrain.h because you put the property declaration in an interface extension in the .m file, which other classes will not see.
To make it publicly accessible move the #property line for whatHappenedSinceLastClear to CalculatorBrain.h, not the .m file.
I can guess that problem lies in the way you assign your stringForDisplay, eg.:
if you use something like
stringForDisplay_ = anotherString;
setter for property doesn't fire, so you have to retain your variable yourself otherwise it'll live just until your method finishes;
If so - use property setters, eg.:
self.stringForDisplay = anotherString;
that way ARC will do all the memory management.
It really depends how you set stringForDisplay inside the performOperation:withArray: method.
for a blind guess, try using
NSString *otherString = self.brain.stringForDisplay;
after this line
double result = [self.brain performOperation:operation withArray:[self.brain whatHappenedSinceLastClear]];
I have a hierarchy of model objects which I will be displaying on different type of UITableViewCell subclasses. All decision is made on the fly as to which model object should be used and corresponding UITableViewCell subclass' object is spawned and then set the model object to the UITableViewCell's subclass object so that it can fetch values from it.
My UITableViewCell hierarchy is something like this:
The base class Cell hierarchy:
#interface BaseCell : UITableViewCell
{
Base *baseObj_;
}
#end
The subclass of cell hierarchy:
#interface DerivedCell : BaseCell
{
}
#property (nonatomic, retain) Derived *derivedObject;
#end
#implementation DerivedCell
#synthesize derivedObject = baseObj_;
#end
The base class of Model object:
#interface Base : NSObject
{
NSString *title_;
}
#property (nonatomic, retain) NSString *title;
#end
The subclass of model hierarchy
#interface Derived : Base
{
NSString *detailedText_;
}
#property (nonatomic, retain) NSString *detailedText;
#end
When I do so, I am having errors in this line:
#synthesize derivedObject = baseObj_;
Which reads:
Property 'derivedObject' attempting to use ivar 'baseObj_' declared in super class BaseCell.
Type of property 'derivedObject' (Derived*) does not match type of ivar 'baseObj_' ('Base * __strong')
I want to use properties and synthesize them so that I can leverage the uses of properties (like using dot notation etc.). I have for now used accessors and setters which solves the problem:
#interface DerivedCell : BaseCell
{
}
-(Derived*)derivedObject;
-(void)setDerivedObject:(Derived*)newDerivedObject;
#end
But I was just wondering if I could somehow fix these errors to use the properties only.
Thanks,
Raj
Try the below code I have modified your code a bit as shown below
Since you can assign class Base object to class Derived in #synthesize, it can be achieved by this way, I know you have tried it already, I have tried it with the below code and able to access the variables with dot, try the below code and let me know if it is not working
#interface DerivedCell : BaseCell
{
Derived *derivedObject;
}
#property (nonatomic, retain) Derived *derivedObject;
#end
#implementation DerivedCell
#dynamic derivedObject;
- (void)setDerivedObject:(Base *)baseObj {
if (self.derivedObject == nil) {
derivedObject = [[Derived alloc] init];
}
derivedObject.detailedText = baseObj.title;
}
- (Derived *)derivedObject {
return derivedObject;
}
#interface Derived : Base
{
NSString *detailedText_;
}
#property (nonatomic, retain) NSString *detailedText;
#end
#implementation Derived
#synthesize detailedText = detailedText_;
#end
#interface BaseCell : UITableViewCell
{
Base *baseObj_;
}
#property (nonatomic, retain) Base *baseObj;
#end
#implementation BaseCell
#synthesize baseObj = baseObj_;
#end
#interface Base : NSObject
{
NSString *title_;
}
#property (nonatomic, retain) NSString *title;
#end
#implementation Base
#synthesize title = title_;
#end
Base *b = [[Base alloc] init];
b.title = #"Hello Raj";
BaseCell *bc = [[BaseCell alloc] init];
bc.baseObj = b;
DerivedCell *dc = [[DerivedCell alloc] init];
dc.derivedObject = b;
NSLog(#"Derive dc %#", dc.derivedObject.detailedText);
Another Solution which I have provided has an issue when I checked it
#interface BaseCell : UITableViewCell
{
NSString *baseTitle_;
}
#property (nonatomic, retain) NSString *baseTitle;
#end
#implementation BaseCell
#synthesize baseTitle = baseTitle_;
#end
#interface DerivedCell : BaseCell
{
NSString *derivedTitle_;
}
#property (nonatomic, retain) NSString *derivedTitle;
#implementation DerivedCell
#synthesize derivedTitle = baseTitle;
#end
When I created instance for the class and as shown below
DerivedCell *dCell = [[DerivedCell alloc] init];
dCell.baseTitle = #"Hello";
NSLog(#"%#",dCell.baseTitle);//Output was Hello
NSLog(#"%#",dCell.derivedTitle);//Output was (null)
It didn't assign the value to derivedTitle, If it is working for you please let me know
Another solution with memory referncing
#interface BaseCell : UITableViewCell
{
NSMutableString *baseTitle_;
}
#property (nonatomic, retain) NSMutableString *baseTitle;
#end
#implementation BaseCell
#synthesize baseTitle = baseTitle_;
#end
#interface DerivedCell : BaseCell
{
}
#property (nonatomic, retain) NSMutableString *derivedTitle;
#end
#implementation DerivedCell
#synthesize derivedTitle;
- (id) init
{
if ( self = [super init] )
{
baseTitle_ = [[NSMutableString alloc] init];
derivedTitle = baseTitle_;
}
return self;
}
#end
DerivedCell *dCell = [[DerivedCell alloc] init];
[dCell.baseTitle appendString:#"Hello"];
NSLog(#"baseTitle : %#",dCell.baseTitle);
NSLog(#"derivedTitle :%#",dCell.derivedTitle);
Console Output baseTitle : Hello derivedTitle :Hello
One pattern I've used for situations like this is to re-declare the property in a category on the derived class. The one structural change this approach requires from the code you posted is that it requires a same-named property (or equivalent getter/setter methods) to be defined in the base class. Consider the following snippet:
#interface BaseModel : NSObject
#end
#interface DerivedModel : BaseModel
#end
#interface BaseCell : UITableViewCell
{
BaseModel *baseObj_;
}
#property (nonatomic, retain) BaseModel *modelObject;
#end
#interface DerivedCell : BaseCell
#end
#interface DerivedCell (DowntypedPropertyCategory)
#property (nonatomic, retain) DerivedModel *modelObject;
#end
#implementation BaseModel
#end
#implementation DerivedModel
#end
#implementation BaseCell
#synthesize modelObject = baseObj_;
#end
#implementation DerivedCell
#end
In this pattern, the base class declares the iVar and the base-typed property, and synthesizes the implementation. The derived class declares the downcast-typed property in a category. Being in a category, the compiler won't force you to implement methods for that property. This gets you out of trying to synthesize against a superclass's iVar, instead relying on implementations that exist in the superclass, but declaring them to be of a different type. At runtime, the runtime will just end up calling the superclass methods (since Obj-C method dispatch is based on selector only, and does not have multiple dispatch.) As a result, clients of these properties can do stuff like this without any compile time warnings or errors:
#interface UnrelatedObject : NSObject
#end
#implementation UnrelatedObject
- (void)unrelatedMethod: (DerivedCell*)dc
{
DerivedModel* dm = dc.modelObject;
NSLog(#"dm: %#", dm);
}
#end
Again, the catch/minor difference is that in order for this to work, the base class must define a property of the same name (or equivalent getter/setter methods). That said, the property/methods in the base class could be declared (or in the case of methods, NOT even delayed) and defined in the base class's implementation file only, and thus would not be visible to other files merely including the header.
One other note: by using this approach you're missing out on compile time checks for things like mismatch between the property specifiers ([nonatomic|atomic], [readonly|readwrite], [assign|retain|copy]). I've found this pattern incredibly useful, but there are some potential pitfalls to keep an eye out for.
I hope I understand the question correctly, how about typing the model as id?
#interface BaseCell : UITableViewCell
#property(retain, nonatomic) id model;
#end
#implementation BaseCell
#synthesize model;
#end
Then the derived cells can use whatever model classes they want.
When you initialize an instance variable through synthesize, that variable is not accesible from any class that may inherit it.
It looks like you may have been trying to point synthesize to a public instance variable and I'm not sure if that is possible. It may be trying to declare a new variable with the same name which I'm sure would generate some compiler warnings at the least since that new declaration would hide an existing one and is less accessible.
You could simply write your own getter and setter to expose the instance variable.
- (Base *) baseObj {
return _baseObj;
}
- (void) setBaseObj:(Base *)val {
if( val != _baseObj ) {
[_baseObj release];
_baseObj = [val retain];
}
}
Hope this helps!
I rarely ask questions, but this one is frustrating me as I can not find an answer anywhere!
I just need to call the function in GameChallenges.m and return the value to the view controller. GameChallenges.m will be called by different view controllers, thats why its separate. Please help!
I have a separate class file called GameChallenges.
This has a function/method in it:
in the .h
#class StatsViewController;
#interface GameChallenges : NSObject {
StatsViewController* statsController;
NSString* challengeTitle;
}
#property (nonatomic, retain) IBOutlet StatsViewController* statsController;
#property (assign) NSString* challengeTitle;
-(NSString*)checkChallenge:(int)challegeID;
#end
in the .m
#import "GameChallenges.h"
#import "StatsViewController.h"
#implementation GameChallenges
#synthesize challengeTitle,statsController;
-(NSString*)checkChallenge:(int)challegeID{
if(challegeID==1){
self.challengeTitle = #"Some Text.";
return challengeTitle;
}else if(challegeID==2){
self.challengeTitle = #"Some Other Text.";
return challengeTitle;
}
}
From a view controller called StatsViewController I am calling this method
in the .h
#class GameChallenges;
#interface StatsViewController : UIViewController {
UILabel* challengeIDDescText;
}
#property (nonatomic, retain) IBOutlet UILabel* challengeIDDescText;
#property (nonatomic, retain) IBOutlet GameChallenges* challenges;
#end
in the .m
[challenges checkChallenge:tempString];
challengeIDDescText.text = challenges.challengeTitle;
Your code is quite weird, I'd say this is what's happening:
-[GameChallenges checkChallenge] seems to expect an int and you call it with a variable called tempString that I guess is an NSString *. More likely than not, your method is ending without assigning challengeTitle and without a valid return value. Fix it with return nil as last statement and passing an int.
This kind of problems are very easy to solve using the debugger.
Also, have a look to Apple samples.
I'm beginner in objective-C, however, code in the GameChallenges.m looks weird to me... Wouldn't this be better?
challengeIDDescText.text = [challenges checkChallenge:challengeId];