I get the feeling that this is a very stupid question, but I cannot find an answer anywhere. I've created a new class in an XCode project called "Word", with its own .h and .m files, which inherits from NSString, and has its own declared instance variable, method, etc. How do I access it within the viewcontroller.h and .m files? I though it would just show up in the little suggestion box in XCode, like the pre-made classe, but it doesn't. How do I use my new class?
#import "Word.h"
I will note that subclassing NSString is extremely uncommon and almost never what you mean to do. You probably meant to have Word have an NSString property.
in your .h, at the top type #import " then start typing Word.h. It should autocomplete if the .h and .m files are in your project correctly.
You just need to add the following to your ViewController.h
#import "Word.h"
Related
I noticed a strange thing in sample code downloaded from apple dev center. the sample code is Footprint: Indoor Positioning with Core Location. There is no #interface and #end in AAPLMKMapRecRotated.h file. But it works well in simulator. Can anyone explain why? Thanks!
"#interface" and "#end" are necessary wherever you want to declare the interface to an Objective-C class. If you don't declare the interface of an Objective-C class in your header, it's obviously not needed. If you declare interfaces of three Objective-C classes in your header, you'll need it three times. If you declare the interface of an Objective-C class in a .m file, so nobody outside that file can see it, then you put it into the .m file.
#interface ... #end declare a ObjC class.. Not all .h file nor all Apple API rely on ObjC, a lot of C is used thorough their framework (CoreAudio, CoreMidi, CoreGraphic, GrandCentralDispatch...) in those framework .h file are classic C header used as such and therefore no #interface .. #end...
I am learning Objective-C and the tutorials I am watching are using an outdated version of Xcode. So, I am not sure whether I created a wrong type of class or if there is something wrong with the code.
In Xcode I Did Command+N do create a new file, clicked 'Source' under 'OS X' and clicked Objective-C File. Then I for file type I chose Category and class: NSObject. In the tutorial the guy made a subclass and since this was the only Objective-C related file in the new Xcode I decided to use this. After making the header and main files, I created the following text.
#import <Foundation/Foundation.h>
#interface NSObject (Person){
NSString *myName;
NSNumber *myAge;
NSNumber *myGrade;
}
#end
Thanks alot, Coler234
A category is an extension of an existing class with some new methods. To indicate you are defining a category rather than a new class, follow the class name with the category name in parentheses as you did in your code(Person). What you actually wanted, though, is a subclass of NSObject called Person, so you need to say
#interface Person : NSObject
I've started a new iOS 5 project and noticed something new at the top of each .m file
#import "HomeViewController.h"
#interface HomeViewController ()
#end
#implementation HomeViewController
#synthesize ...
Is this extra #interface ... required if I have a separate .h file?
Why did this not show up in pre iOS 5 projects?
Can I use this instead of having a separate .h file?
What is the best practice for this going forward?
That's a class extension. You can use it to make declarations that you don't want to be in the .h file.
This was used by many developers, even before, who manually added the extension in the .m file. So I guess Apple included this in the template because it is widely used and is considered a good practice.
In fact, the .h file should only be used to make declarations that are going to be used from other files. You may have to declare some properties, methods or constants that will only be used inside the .m file. For those declarations, it is better to make them in the class extension.
So to answer your questions:
Is this extra #interface ... required if I have a separate .h file?
No, it is not required but is a best practice.
Why did this not show up in pre iOS 5 projects?
Even if this was a commonly used practice, it was not included in the template.
Can I use this instead of having a separate .h file?
No. The class extension doesn't replace the .h file where you have to declare the "public" interface of your class.
What is the best practice for this going forward?
You should put in the class extension all the declarations that don't need to be visible outside of the .m file.
The interface section in the implementation file allows you to declare variables, properties, and methods that are private, meaning that they won't be seen by other classes.
No, it's not required at all. But I use it as much as possible and only make public those things that other classes need to see.
I'm trying to learn some of the basics of developing OS X apps with XCode and Objective-C, but I am already running into problems.
I have a project I made from a while back which worked very well for me, however, when I try to replicate the results I had last time, I run into numerous errors.
I have two files, a .c and a .h named "AppDelegate"
in AppDelegate.h:
#import <Cocoa/Cocoa.h>
#import <WebKit/WebView.h>
#interface AppDelegate : NSObject {
IBOutlet WebView *gameFrame;
}
#end
then, in AppDelegate.c:
#import "AppDelegate.h"
#implementation AppDelegate
-(void)awakeFromNib
{
}
#end
In IB, there is an NSObject named 'AppDelegate' and its class is 'AppDelegate'.
However, when I try to run this, I get 11734 errors...
When I click on the error icon at the bottom of the XCode window, it lists a bunch of code that seems to be involving NSStrings, but I cant make any sense of it...
Also, within my code, the
#end
line in both the .c and the .h are highlighted with an error saying:
'Expected identifier or '(' before '#' token.'
I don't understand what XCode is tripping up on when it tries to compile, I don't see any logical place for a '(' to go and I don't think I left anything unidentified.
Any help would be appreciated.
That's because that isn't valid C code.
You named your module file AppDelegate.c, which indicates that it contains source code written in (more or less) pure C. But it does not: You wrote a class interface and implementation in Objective-C, which is a superset of C (all C is valid Objective-C, but not all Objective-C is valid C—in particular, classes aren't).
For this, you must name the module file AppDelegate.m (or anything else, as long as it ends with .m; naming it after the class is a convention worth following). The .m suffix indicates a module (usually containing a class implementation) written in Objective-C.
So, just rename your module file from AppDelegate.c to AppDelegate.m. Make sure you do this in Xcode, not the Finder: If you do it in the Finder, Xcode will only care that there is no longer a file named AppDelegate.c; it won't notice the rename.
For your convenience in creating future classes, Xcode provides a template in the “New File” panel for creating subclasses of certain Cocoa classes; your AppDelegate should be a subclass of NSObject, and templates are also provided for NSView, NSDocument, UIView, UIViewController, and a few others. The files created by the template will already have the correct extensions.
I've run into an Objective-C problem that doesn't seem to make any sense to me. I am a relatively well-versed ObjC programmer and understand the whole "forward declaration" concept, but this one has me scratching my head. So here's the deal:
ClassA is a class in my Xcode project that is project-only.
ClassB is a subclass of ClassA which is public and is imported into my framework's header.
I am getting a "Cannot find interface declaration for 'ClassA', superclass of 'ClassB'..." error when building. I have already put the #class ClassA; forward declaration in ClassB.h, but that does not seem to solve the problem. When I change the #class ClassA; to #import ClassA.h, it works fine. However, since ClassA is project-only, dependent projects cannot build ClassB because it cannot access ClassA's source.
Any help would be appreciated and I hope that makes sense. Thanks!
The problem is that you have an infinite loop in your #imports.
The solution: all #imports go in the implementation file and all classes needed are declared in the .h files.
To subclass a class, the superclass's full declaration must be available to the compiler. #class just enables references to instances of said class -- allows for A *foo;.
Subclassing requires more metadata (at least, it did under the legacy runtime -- I think it might be possible to support subclassing without the full super's #interface. Technically possible, but probably not useful.)
I have an answer: You must check your '#import' order. Before you use the superclass it should be imported and compiled.
I had an issue where I was using categories in a superclass method and was getting this inheritance error. Once I moved the categories .h imports to the superclass .m file thing started getting better.
Just carry out all possible headers from .h to .m file of superclass and see which one is the matter of the problem. I'm sure that it's one of common headers used in both classes.
Like #Igor said, the order of imports matters:
I had to change
#import <KeychainItemWrapper/KeychainItemWrapper.h>
#import <Foundation/Foundation.h>
to
#import <Foundation/Foundation.h>
#import <KeychainItemWrapper/KeychainItemWrapper.h>