Objective-C，is a reflective, object-oriented programming language that adds Smalltalk-style messaging to the C programming language.Today, it is used primarily on Apple's Mac OS X and iOS: two environments derived from the OpenStep standard, though not compliant with it.[1] Objective-C is the primary language used for Apple's Cocoa API, and it was originally the main language on NeXT's NeXTSTEP OS. Generic Objective-C programs that do not use these libraries can also be compiled for any system supported by gcc or Clang.
1. Define and implement a class
int the *.h file
@interface ClassName : ItsSuperclass
{
instance variable declarations
}
//method declarations
+ alloc; //class methods are preceded by a plus sign can be used by class objects,
- (void)display;// instance methods are marked with a minus sign can be used by instances of class
Class methods are methods which are declared as static. The method can be called without creating an instance of the class. Class methods can only operate on class members and not on instance members as class methods are unaware of instance members. Instance methods of the class can also not be called from within a class method unless they are being called on an instance of that class.
Instance methods on the other hand require an instance of the class to exist before they can be called, so an instance of a class needs to be created by using the new keyword. Instance methods operate on specific instances of classes. Instance methods are not declared as static.
@end
in the *.m file
@implementation ClassName : ItsSuperclass
{
instance variable declarations
}
//method definitions
-(void)display
{ // implement }
@end
Declaring a Class, notes:
1 Every class should subclass NSObject;
2 class that inherits NSObject Provides a lot of basic functionality, including memory management;
3 No constructors but Apple uses conventional initializers
4 Override –[NSObject dealloc] to free resources and memory, Always call super’s implementation
Never access any ivar or call methods after the call to [super dealloc].
Never call dealloc directly!
2. Calling method
[object method];
[object methodWithInput:input];
3.Creating Objects
example:NSString* myString = [[NSString alloc] init];
This is a nested method call. The first is the alloc method called on NSString itself. This is a relatively low-level call which reserves memory and instantiates an object.
The second piece is a call to init on the new object. The init implementation usually does basic setup, such as creating instance variables. The details of that are unknown to you as a client of the class.
In some cases, you may use a different version of init which takes input:
NSNumber* value = [[NSNumber alloc] initWithFloat:1.0];
4 Muti-input function
(method type) FuncName: (type of arg 1) name of arg1 Name of arg2: (type of arg2) arg3 name …. ;
example；
-(void) setKids: (NSString *)myOldestKidName secondKid: (NSString *) mySecondOldestKidName thirdKid: (NSString *) myThirdOldestKidName;
5 Difference between C and Objective C
BOOL，YES，NO：YES is equal to the true in C# or Java，NO is equal to false。But the value of YES is 1，NO is 0
nil means a null pointer.
”String” is a C string, @”"convert a C string to NSString.
define the access type:
@property( attributes) type name; attributes includes readwrite readonly assign retain copy noatomic
example: @property(readwrite, assign) int fido;
Basic Constructs
Objective-C Summary
| Language Example |
Description |
[ class_name method ];
object = [[ class_name alloc] init ];
object = [ class_name new ];
[ object method ];
[ object free ];
[ object release ];
class_name *object;
object = [[ class_name alloc] init ];
object = [ class_name new ];
[ object method ];
[ object free ];
[ object release ];
class_name *object; |
Invoking methods. Some methods sent to class, some to object.
alloc/init are the same as new.
For objects derived from Object class.
For objects derived from NSObject.
You can’t instantiate an object on the stack; you can only have pointers to them. |
@interface class_name : base_class
{
int data_member;
}
- (return_type) object_method;
+ (return_type) class_method;
@end
int data_member;
}
- (return_type) object_method;
+ (return_type) class_method;
@end |
Class declaration. |
@implementation class_name;
- (return_type) object_method
{
}
+ (return_type) class_method
{
}
@end |
Class definition. |
| @class class_name; |
Forward declaration of class. |
- (void) method;
[ object method ];
- (return_type) method: (type) arg;
val = [ object method:1 ];
- (void) method: (type) arg1 arg_name: (type) arg2;
[ object method:1 arg_name:2 ];
name is ìmethod:arg_name:î
[ object method ];
- (return_type) method: (type) arg;
val = [ object method:1 ];
- (void) method: (type) arg1 arg_name: (type) arg2;
[ object method:1 arg_name:2 ];
name is ìmethod:arg_name:î |
No argument, no return.
Single argument with return value.
If more than one argument, their names are part of the method name. Using the names on calls is optional but recommended.
Use this name in @selector. |
SEL selector = @selector(method);
SEL selector = @selector(method:);
SEL selector = @selector(method:arg:);
[ object perform:selector ]; |
Gives a selector to a method. If it has arguments they are part of the name. A method with one argument ends in a colon.
Invoke a method specified by a selector. |
id
id object; |
Object of any type; often used as a return value.
Notice no *: can hold an object of any type, but if you invoke a method it doesn't have, you crash. |
| #import |
An #include that's only included once. |
self
[ self method ]
[ self class ]
[ self method ]
[ self class ] |
The object whose method is being executed.
Invoke one of your own methods.
Returns the class you belong to; useful if you've been subclassed. |
super
[ super method ];
[ super method ]; |
The parent object; always exists because everything is derived from Object or NSObject. |
class_obj = [ class_name class ];
class_obj = [ object class ];
f = [ object isKindOf:class_obj ];
f = [ object isMemberOf:class_obj ];
f = [ object respondsTo:selector ];
f = [ class_name instancesRespondTo:selector ]; |
Gives the class object for the named class.
Gives the class object for the named object.
Is object a member of class_obj or one of its descendants?
Is object a member of class_obj ?
Can object respond to the method described by the selector?
Can instances of the given class respond to the method? |
f = [ object isKindOfClass:class_obj ];
f = [ object isMemberOfClass:class_obj ];
f = [ object respondsToSelector:selector ];
f = [ object isMemberOfClass:class_obj ];
f = [ object respondsToSelector:selector ]; |
NSObject versions of the introspection messages. |
@public
@protected
@private
@protected
@private |
You can specify scope for data members only.
Allows access via object->data_member.
The default for instance variables.
Only methods of this class (not derived classes) can access this member. |
@interface class_name(category)
@interface class_name(category) <protocol> |
Categories define new methods or data members for an existing class.
You can override a method from the original class definition, but then that original is lost; subclassing might be better. |
@protocol p1
- methods
@end
@protocol p1 <p2>
@interface class_name : base_class <p1, p2>
f = [ object conformsTo: @protocol(p1) ];
id <p1> object;
id <p1, p2> object;
@protocol p1 <p2>
@interface class_name : base_class <p1, p2>
f = [ object conformsTo: @protocol(p1) ];
id <p1> object;
id <p1, p2> object; |
Protocols define a set of methods shared between classes. You must define these methods, but don't declare them in the interface.
A protocol can include another one.
This class is based on two protocols.
True if the object conforms to a protocol; if so you can use all its methods.
Restricts the object pointer to a type that conforms to these protocols. |
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posted on 2012-05-18 14:31
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