xcode basic explanation needed

I am actually a newby at xcode. I can make out a few things be myself but have questions about what some things do and why they are put there. I have tried to read many e-books, watched tutorials, but they never go into the basics, alway just say "Add this, Click here etc"

Could someone give me some answers to a few questions please. Ok, I know an ios app is mostly made out of Views, views are controlled by controllers. Each controller has a header (.h) file and a module?class? file (.m). The .h file contains the declarations of variables and functions used in the .m file. The whole app is controlled by a master "controller" called the "delegate". Definitions in .h file may be for example an action IBAction or IBLabel or something.

What raises questions for me is for example these lines:

@class FlipsideViewController;

@protocol FlipsideVi开发者_如何学编程ewControllerDelegate
- (void)flipsideViewControllerDidFinish:(FlipsideViewController *)controller;
@end

@interface FlipsideViewController : UIViewController

@property (nonatomic, assign) id <FlipsideViewControllerDelegate> delegate;

- (IBAction)done:(id)sender;

and why are sometimes in another view controller the delegate class loaded

@class MainViewController;

what does the following do, meaning what is the @interface declaration?

@interface flipAppDelegate : NSObject <UIApplicationDelegate>

what is

nonatomic, retain

sorry for asking really stupid questions, but every tutorial just skips these things. I can follow a youtube video or a manual, but it doesn't teach me a lot...

Let me try to answer your questions, one at a time.

what is the @interface declaration?

The interface declares a class. By declaring a class, I mean it specifies the instance variables and private/public methods that it contains. Again, the header file only contains the declaration of the methods, and the implementation/body of the methods lies in the module class. So, here-

@interface FlipsideViewController : UIViewController

The class FlipsideViewController derives from/subclasses/extends UIViewController. i.e Is a type of UIViewController but adds its own features.

Similarly

@interface flipAppDelegate : NSObject <UIApplicationDelegate>

Subclasses NSObject and implements the UIApplicationDelegate protocol. A protocol is essentially a set of methods that a class promises to implement (although there can be optional methods).

why are sometimes in another view controller the delegate class loaded

The delegate pattern allows a class to delegate its work to another class that implements the delegate protocol. So, here, FlipsideViewController keeps an instance of the delegate object, so that its flipsideViewControllerDidFinish: can be called.

what is nonatomic, retain

It means that when you set a value to your instance variable, the value's refcount will be incremented and set to your variable. Also, it will not happen as an atomic operation. You need atomic only in a multi-threaded environment.

@synthesize is simply a shortcut to generate getters and setters for your variables.

You really need to read the Objective-C Programming Language from Apple. It's pretty brief, and runs down the basics of the architecture, concepts, and syntax.

To address, briefly, some specifics:

• The @class directive is used to declare the name of a class without importing it's header file. It is often used in a .h file declaring a protocol, because a protocol has no implementation, it doesn't need to import the interfaces of other classes (their .h files).
• A protocol is a way of declaring what methods and properties a class should have in order to "implement" the protocol.
• @interface is used in an interface file (.h) to declare a class, meaning to describe the methods and properties it will have, the protocols it will implement, and the superclasses from which it will inherit. In your example, the class will be called flipAppDelegate, which inherits all of the methods and properties of the NSObject class, and which implements the UIApplicationDelegate protocol.
• In your class (.m) file, you will define (with all your code) all of the methods and properties that you declared in your interface file. You include the methods and properties you declared yourself, and from the protocols you implement.
• @synthesize is used in a class implementation file (.m) to "synthesize" --- that is, automatically create the code for --- all the properties you declared in your interface (.h) file. Since properties normally just need basic accessors (a "getter" that just returns the current value, and a "setter" that just sets the current value), using @synthesize is a shortcut to let the compiler create the variable to store the value, the getter method, and the setter method for you automatically.

• Xcode = An IDE (Integrated Development Environment)
• Objective-C = A Language
• Cocoa Touch, Media FrameWork, Core FrameWork = Frameworks used in developing for iOS

I'd highly recommend starting by learning Objective-C. At least with a primer first:

https://developer.apple.com/library/ios/#referencelibrary/GettingStarted/Learning_Objective-C_A_Primer/_index.html

There's a wealth of tutorials and videos available from Apple for developers you might want to start on the developer portal.