This question pops up quite often here, even if just implicitly when users mistag their iOS questions. So, what’s the difference between Xcode, Objective-C and Cocoa?
Objective-C is a programming language. It could be said that it’s just a description of what valid Objective-C programs look like and what they mean. If you have a source code listing written in Objective-C, you need an interpreter or a compiler to put the listing to work. Languages like Objective-C are usually compiled, so most people use a compiler (like LLVM). Objective-C is almost exclusively used to develop for iOS and OS X, but there are other uses, too – as an example, some people write Objective-C for Linux.
You can use a text editor to write the sources and a compiler to turn them into an actual programs, but with modern technologies there’s much more to take care of, so that there is another program to make your job easier. These are called Integrated Development Environments, or IDEs. An IDE offers you a convenient way to edit the sources, compile them, debug the resulting programs, read the documentation, and many other things. Xcode is one such IDE. An important observation here is that Xcode does not compile your sources itself, it just calls the standalone compiler (LLVM). And Xcode is not the only IDE you can use to develop Objective-C apps – there’s AppCode, for example.
Writing iOS or OS X apps from scratch each time would be very time-consuming. That’s why Apple provides the developers with a good set of libraries. The libraries are simply a huge amount of source code written by Apple, and this source code takes care of most things that apps have in common. These libraries are called Cocoa.
Now, if you can’t figure out how to extend a class, you are most probably talking about Objective-C. It doesn’t have anything to do with Xcode or Cocoa, you could be very well writing some GNUstep code for Linux using Vim as an IDE and GCC as a compiler. On the other hand, if your Xcode build process fails because of some mysterious setting, or if you’re trying to build a static library in Xcode, that’s clearly an Xcode issue. And if you can’t figure out how to use some NSObject facility or the NSFileManager class, that’s Cocoa. (But it doesn’t have to be Xcode-related, as you could use AppCode or TextMate as your IDE!)
Originally available on my blog. Feel free to link to the blog post or this question when retagging or explaining the difference.
Xcode is the integrated development environment (IDE)—the application—that developers use to write software for iOS and/or OS X. It includes the editor, the build system (determining what to build to produce the desired target), and quite a few other things.
Objective-C is the main language that developers write such software in. They may write bits of it in pure C, use C++ or combine it with Objective-C (producing Objective-C++), or write some or all of the program in another language entirely, such as MacRuby, Java (with j2objc), or C# (with MonoTouch).
Xcode includes the Clang compiler, which turns code written in Objective-C, C, and a few other languages into executable code. Most error messages come from Clang, and Xcode relies heavily on it for search indexing, syntax highlighting, and name completion of Objective-C code.
Cocoa and Cocoa Touch are application frameworks. Each one is a suite of many individual frameworks (libraries stored in folders named blahblah.framework), such as:
Foundation (both): General object-oriented utilities, including NSString, NSURL, NSFileManager, etc.
Core Foundation (both): Mostly the same thing, but different, mainly in having a C-based API rather than Objective-C
Application Kit (Mac): Application and windowing framework
UIKit (iOS): Application and windowing framework
Core Graphics (both): Drawing
Core Animation (both): Sprite-management and animation framework
(and many, many more where they came from, especially on the Mac)
So:
You can use a framework besides Cocoa or Cocoa Touch, but you'll have to have some Cocoa/Cocoa Touch code, at some level, in order for your application to talk to the system, receive events, draw, etc. Frameworks that specifically target Mac and/or iOS will include the relevant wrappers for you, at varying levels of quality.
You can use a language besides Objective-C, but you'll have lots of syntactic awkwardness, as most of Cocoa and Cocoa Touch are designed for Objective-C's unique syntactic features (particularly selectors).
You can use an editor besides Xcode, and you can even use a build system besides Xcode (such as make), but Apple's App Stores expect apps built a particular way (especially with regard to code signing), so unless you're not targeting the App Stores, any other build system has to replicate what Xcode does or risk its users getting rejections.
A clear mistake is failing to differentiate Xcode from everything else. Xcode is the tool you are using to program in - to edit code, run code, etc. So if you are having trouble with the tool (e.g., the window doesn't show you your code properly, or you're having trouble drawing your interface, etc.), that's an Xcode problem.
If you don't understand why your code doesn't work, you're probably having an Objective-C problem or a Cocoa problem. But you won't necessarily know which.
It's an Objective-C problem if the root of your trouble is that you don't know how the language works (e.g. you don't know what the asterisk is for, or that declaration is not instantiation, or that messages to nil do not error out but don't do anything either).
It's a Cocoa problem if you don't grasp the delegate architecture or how a view controller works.
But my experience of the way people pose questions is that you may be ignorant of which of these you are ignorant of. I don't mean you personally, I mean all of us. This can make it difficult to pose the question properly because you don't know what exactly it is that you don't know — if you did, you'd know it and you probably wouldn't be having a problem (you'd be fixing the problem and on to the next thing).
Are there frameworks/generators for producing iOS code from any other language?
A dynamic language like JavaScript, ruby or Python are preferred. Googling for iOS code generators was largely fruitless.
The problem with systems like PhoneGap is that their output is a full-fledged application. What I need to produce is a library (.a & .h file eventually) that other Objective-C developers can reuse in their projects.
RubyMotion may or may not do what you want. I haven't seen much about the practicalities of it yet, but I'm thinking since it's statically compiled chances are good that it can produce libraries that can be simply linked into Objective-C projects. One might need another tool to produce the header files.
Of course, this is all speculation.
I think the best solution for what you're looking for is Titanium. It has its own sdk (in JavaScript), a complete IDE and allows you to have one codebase for all major platforms (iOS, Android included). What it's really awesome is the fact that it actually generates native code (a valid XCode project or a Java one for Android). It's also free and open source. Definetely worth a look.
I've never seen code generators, but there are a variety of "spoofs" as it were.
http://xamarin.com/monotouch - iOS on C#
http://phonegap.com/ - iOS on HTML, CSS , Javascript
http://ipodtoucher55.blogspot.com/2010/06/how-to-create-iphone-apps-in-flash-cs5.html - one of several tutorials for flash on iOS
I've seen links to python libraries and I think java too.
When it comes down to it though, they're all work arounds, not direct development.
I was looking at doxygene and I noticed that its output for objective-C is less than optimal, so I was looking at doxygene's internals(in which all syntax analyzers consolidated into a huge blob), and then I decided that it was going to take a lot of work just to figure out where to begin with that.
So I thought, ok let's start by creating a dictionary/tree from an objective-c source file which it seems Xcode does already(because symbols are search able). And it seems to use LLVM"clang" somehow. Does anyone know how I can invoke "clang" to return a structure of the symbols in a project/document?
Xcode doesn't directly use the "clang++" binary for this purpose. The clang++ binary is actually a very small wrapper around the Clang C++ libraries. Xcode uses libclang (a C wrapper around the C++ libraries) for its C++ parsing needs.
Thus, to get the information you want, you will need to use libclang. On this page are the slides and video of a presentation Doug Gregor (the main developer of Clang) gave at the 2010 dev meeting entitled "libclang: Thinking Beyond the Compiler".
Many people in the clang community have expressed interest in replacing Doxygen's parser with clang. So you are not alone. However, I believe it is not a small project.
I would like to know how I can import a library into Objective-C at runtime. I'm new to Objective-C and this may be a complex question, but I'm fairly proficient in C/C++,
I'm developing a modular application where specific modules (libraries) are loaded as needed. Basically I have a name in runtime, like "nodeX", and I want to load a library that has it.
I've been searching for a way to do this but have been unsuccessful.
Thanks!
See NSBundle.
Note that you can't safely unload code on Mac OS X, Objective-C or otherwise, unless you are so terribly careful that it just isn't worth the effort to do so.
Note, also, that you can't dynamically load code on iOS.
I'm trying to re-write an old image-viewing plugin for the mac. The old version uses QuickDraw (I said it was old) and resources (really really old) and so it doesn't work in Firefox 3.6 (which is why I'm re-writing it)
I know some Objective C, and so I figure I'm going co re-write this in that using new-fangled Mac routines and nibs, etc. However, I don't know how to start. I've got the BasicPlugin example that comes with mozilla source, so I know how to create a plugin with entrypoints, etc. However, I don't know how to create the nib, and how to interface Obj-C with the entrypoints, etc.
Does anyone know of a more advanced sample for mac than BasicPlugin.bundle? (Preferably simple enough that I can just look at it and understand it...)
thanks.
Sadly i don't really know of any good "intermediate" example. However, integrating Obj-C isn't that difficult. Thus, following is a short overview of what needs to be done.
You can use Obj-C and C/C++-sources in the same project, its just recommendable to keep them seperated to some extent. This can for example be done by letting the source file with the entry-points and other NPAPI-interfacing stay plain C or C++ files and e.g. forward calls into the plugin from there.
Opaque pointers help to keep a clean seperation, see e.g. here.
The main changes to your plugin include switching to different drawing and event models. These have to be negotiated in NPP_New(), here is an example for the drawing model. When using Cocoa and to support 64bit enviroments, you need to use the Cocoa event model.
To draw UI elements you should be able to use a NSGraphicsContext from the CGContextRef and then draw an NSView in the context. See also the details provided in this post and its follow-ups.