I have a variable x in one class.And I want to access the updated x value in some other class.
There is so much of confusion.Can I use property?.Please help me.
Thanks in advance
Do you mean that you want to be told when the value changes? Have a look at Key Value Observing
To simply access an iVar in one class from another, a property is exactly what you want.
The syntax is :
in your .h
#interface myclass : NSObject {
UIWindow *window;
}
#property (nonatomic, retain) UIWindow *window;
#end
in your .m
#implementation myclass
#synthesize window;
...
#end
The #synthesize directive instructs the compiler to produce a lot of boilerplate code (as directed by the (nonatomic, retain) specifiers. In this case to handle thread safety and memory management.
Also note that in Objective-C 2.0 the iVar declaration UIWindow *window; is not required.
If you want to be notified in your second class when an iVar is updated, you need to look at key value observing. Unless you are writing a framework or some very dynamic code, that is probably overkill.
Maybe this tutorial will help you out..
If this is not what you mean, please rephrase the question, because i don't understand it..
Edit: Or a shared Instance can be used
you could access it by #import Classname, and then just use the getter that is created with the property. but first initialize the class you have imported..
#import "ClassY.h"
#implementation ClassX
ClassY * classY;
NSString * name;
...
name = [classY name];
...
#end
Related
I'm trying convert my code to Modern Objective-C style. How i read here http://www.techotopia.com/index.php/The_Basics_of_Modern_Objective-C": "In the case of Modern Objective-C, however, the synthesis takes place by default, making the use of #synthesize declarations unnecessary. When using default property synthesize, instance variable properties are accessible from within code using the property name prefixed with an underscore."
However, I have:
Relationship.h
#interface Relationship : NSObject <NSCoding>
//...
#property(nonatomic, weak) Person* first;
//...
#end`
OtherRelationship.h
#import "Relationship.h"
#interface OtherRelationship : Relationship
#end
OtherRelationship.m
#import "OtherRelationship.h"
#implementation OtherRelationship
#synthesize first = _first;
- (void)foo
{
NSLog(#"%#", _first);
}
and it's working. But when i delete
#synthesize first = _first;
i get "Use of undeclared identifier '_first'" error. Does inheritanced variables doesn't work with autosynthesize or should i looking for problem elsewhere?
The backing ivar in the superclass is #private to the subclass. That is, the subclass may call self.first, but not _first. If you want to #synthesize again, use a different name because you can't refer to _first. For example, replace with #synthesize first = _ffirst; or just drop the #synthesize.
I'm having a hard time understanding why the following textfield is declared twice in some tutorials.
In the .h file:
# include <UIKit/UIKit.h>
#interface MyViewController : UIViewController {
UITextField *name; // <----- What do I need this for? Is it the same as below?
}
#property (nonatomic, strong) IBOutlet UITextField *name; // <----- Same as this?
#end
At first I thought this would be something like an instance variable, but they are only declared here in the .m file, right?
.m file
#import "MyViewController.h"
#implementation UIViewController {
NSString *myString; // <----- This is an instance variable, right?
}
What's the "UITextField *name;" for? Don't I only need the second one with the #property in front? Thank you.
This is an old way, just use property is OK.
If you declare both, you must use #synthesize name; in your .m file to make self.name same as name.
XCode4.2 auto synthesize name = _name. So use self.name as much as possible in your .m file.
Variable in {} just use for internal or private, when you don't want implement setter and getter.
If you are targeting iPhone OS or 64-bit Mac OS X then you do not need to define ivars for your properties. Take a look at Dynamic ivars: solving a fragile base class problem
I may not have worded the question right, but I am not sure if what I am asking makes 100% so here goes:-)
In Xcode you can set a #class (name of class) above the #interface in the header file.
Is this the same as changing the the UIViewController in the name of the class? See code below:
So is this the same -
#class CoreDataClass;
#interface FlipsideViewController : UIViewController <UITableViewDataSource, UITableViewDelegate>
{
}
//This file declares the UITableView
#property (nonatomic, retain) IBOutlet UITableView *mainTableView;
#property (nonatomic, retain) CoreDataClass *cdc;
As this:
#interface FlipsideViewController : CoreDataClass <UITableViewDataSource, UITableViewDelegate>
{
}
//This file declares the UITableView
#property (nonatomic, retain) IBOutlet UITableView *mainTableView;
#property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;
#end
??
If this is not the same, how is it different and what are advantages to the different implementation?
The Difference is only really asked if they are similar:-)
#class is not used to create a class, but to forward declare another one. See this question for a good explanation.
They are not the same at all. The first case is a 'forward declaration' - you are telling the compiler that the class CoreDataClass exists, so that you can refer to it in your header file without actually importing the files that define it.
The second case, you are declaring that FlipsideViewController is a subclass of CoreDataClass, and inherits all its methods and instance variables.
They're not even related. The difference is that the superclass ("parent" class) of your view controller will be different (and this can lead to nice unrecognized selector errors...). Forward-declaring a class using the #class keyword is just a convenient way of referring to a class when one doesn't want to import a whole framework header hierarch just in order to refer to one class. I. e., if you don't need to know anyting about a class except that it exists, you can use this keyword. Be careful, however, if you maks heavy use of the class - in those cases, the class forward-declaration is not considered a good solution.
In first case when you use #class it's inform XCode that you will be using CoreDataClass somewhere and you will #import header for example in .m file, in second case you're inherit from CoreDataClass (you will get access to all public and protected properties)
I am getting an error as:
protocol declaration not found
I couldn't find out what's the reason. Now I am using ARC. I doubt that the issue is due to that. Here is the code I am using for protocol declaration
//This is the first page we are declaring the Delegate
.h
#protocol ImageDelegate
#optional
-(void)ImageSelected:(UIImage *)ImageName;
#end
#interface GetAddedMovieList : UIViewController<UITableViewDataSource,UITableViewDelegate>{
id<ImageDelegate> delegate;
}
#property(nonatomic, strong)id<ImageDelegate> delegate;
#end
.m
#synthesize delegate;
//This is page in which i tried to set delegate. Here I am getting the error.
#interface ImageEnlarge : UIViewController<ImageDelegate>{
IBOutlet UIImageView *imgEnlarge;
NSString *stgImageName;
}
I see several (possible) issues in your code.
#property(nonatomic, strong)id<ImageDelegate> delegate;
delegates should be weak. GetAddedMovieList do now own the delegate by any mean and therefore shouldn't have an impact on its life cycle.
#synthesize delegate = delegate;
By default #synth uses either ivar_ or _ivar lately. With the latest LLVM #synth aren't necessary anymore btw, neither ivars.
#synthesize outside an #implementation ?
Have you checked your #imports?
It's probably an import loop. Do you #import the correct file for where you are using the protocol? And are you importing that file in the protocol file? If so then you have an import loop. Use forward declaration in the protocol's header instead and that should solve it. (#class)
You are putting an #interface on a .m file, are you trying to create a private #interface? With an IBOutlet declared there?
After seeing your edit, I am guessing there is only missing an import on the .h of your ImageEnlarge class.
Try like it.
#protocol ImageDelegate<NSObject>
#optional
-(void)ImageSelected:(UIImage *)ImageName;
#end
And also add this property.
#property(nonatomic,assign)id<ImageDelegate> delegate;
I think it will be helpful to you.
I've attempted to compile, but every time I do, one method throws a strange "expected a type" error. I have a method in the header:
-(ANObject *)generateSomethingForSomethingElse:(NSString *)somethingElse;
The error points at the return type for this method. I've imported ANObject into the header using #import "ANObject.h" and ANObject is compiling fine..
Why is this happening?
This is to do with the order that the source files are compiled in. You are already probably aware that you can't call a method before it is defined (see below pseudocode):
var value = someMethod();
function someMethod()
{
...
}
This would cause a compile-time error because someMethod() has not yet been defined. The same is true of classes. Classes are compiled one after the other by the compiler.
So, if you imagine all the classes being put into a giant file before compilation, you might be able to already see the issue. Let's look at the Ship and BoatYard class:
#interface BoatYard : NSObject
#property (nonatomic, retain) Ship* currentShip;
#end
#interface Ship : NSObject
#property (nonatomic, retain) NSString* name;
#property (nonatomic, assign) float weight;
#end
Once again, because the Ship class has not yet been defined, we can't refer to it yet. Solving this particular problem is pretty simple; change the compilation order and compile. I'm sure you're familliar with this screen in XCode:
But are you aware that you can drag the files up and down in the list? This changes the order that the files will be compiled in. Therefore, just move the Ship class above the BoatYard class, and all is good.
But, what if you don't want to do that, or more importantly, what if there is a circular relationship between the two objects? Let's increase the complexity of that object diagram by adding a reference to the current BoatYard that the Ship is in:
#interface BoatYard : NSObject
#property (nonatomic, retain) Ship* currentShip;
#end
#interface Ship : NSObject
#property (nonatomic, retain) BoatYard* currentBoatYard;
#property (nonatomic, retain) NSString* name;
#property (nonatomic, assign) float weight;
#end
Oh dear, now we have a problem. These two can't be compiled side-by-side. We need a way to inform the compiler that the Ship* class really does exist. And this is why the #class keyword is so handy.
To put it in layman's terms, you're saying, "Trust me man, Ship really does exist, and you'll see it really soon". To put it all together:
#class Ship;
#interface BoatYard : NSObject
#property (nonatomic, retain) Ship* currentShip;
#end
#interface Ship : NSObject
#property (nonatomic, retain) BoatYard* currentBoatYard;
#property (nonatomic, retain) NSString* name;
#property (nonatomic, assign) float weight;
#end
Now the compiler knows as it compiles BoatYard, that a Ship class definition will soon appear. Of course, if it doesn't, the compilation will still succeed.
All the #class keyword does however is inform the compiler that the class will soon come along. It is not a replacement for #import. You still must import the header file, or you will not have access to any of the class internals:
#class Ship
-(void) example
{
Ship* newShip = [[Ship alloc] init];
}
This cannot work, and will fail with an error message saying that Ship is a forward declaration. Once you #import "Ship.h", then you will be able to create the instance of the object.
I found this error hapenning when there is circular dependency on the headers. Check if the .h file where you declare this method is imported in ANObject.h
You basically add
#class ANObject;
before #interface!
So, for some reason I was getting this error while trying to set a method with an enum type in the parameters. Like so:
- (void)foo:(MyEnumVariable)enumVariable;
I had previously used it like this and never had an issue but now I did. I checked for circular dependency and could find none. I also checked for typos multiple times and no dice. What ended up solving my issue was to adding 'enum' before I wanted to access the variable. Like so:
- (void)foo:(enum MyEnumVariable)enumVariable;
{
enum MyEnumVariable anotherEnumVariable;
}
Usually when I see an error like this it's because I have a typo on a previous line, such as an extra or missing parenthesis or something.
It may sound stupid, but wrong shelling or wrong use of uppercase/lowercase letterwrong case this.
I got this message, when the variable type was misspelled. See below this below
e.g.
-(void)takeSimulatorSafePhotoWithPopoverFrame:(GCRect)popoverFrame {
instead of.....
-(void)takeSimulatorSafePhotoWithPopoverFrame:(CGRect)popoverFrame {
Strangely enough, changing the order of my imports has fixed this in the past... Try moving the import to the bottom after all your other imports.
I solved it by adding #class class_name to the .h file