[Objective-C] Classes 筆記 (1) - 基本的實作與宣告

@interface - 可以宣告在header file(.h) 或是 implement file(.m)

• Declare a class

@interface MyClass : NSObject {
}

• Declare View Controller Class

@interface MyViewController : UIViewController {
}

@implementation

• MyClass.m

#import "MyClass.h"

@implementation MyClass

@end

@class

如果要用到此程式以外的Class, 用#import 載入

Example: 在MyClass中Import AnotherClass

• AnotherClass.h

//--AnotherClass.h--
#import <Foundation/Foundation.h>

@interface AnotherClass : NSObject {
}

@end

• MyClass.h

//--MyClass.h
#import <Foundation/Foundation.h>
#import "AnotherClass.h"

@interface MyClass : NSObject {
  //--an object from AnotherClass--
  AnotherClass *anotherClass;
}

@end

如果在AnotherClass中也要用到MyClass, 不能在AnotherClass中也#import MyClass, 要用 @class

• AnotherClass.h

//--AnotherClass.h--
#import <Foundation/Foundation.h>

@class MyClass;

@interface AnotherClass : NSObject {
}

@end

• MyClass.h

//--MyClass.h
#import <Foundation/Foundation.h>
@class AnotherClass;

@interface MyClass : NSObject {
  //--an object from AnotherClass--
  AnotherClass *anotherClass;
}

@end

@class 只是先告訴Compiler, 這個anotherClass變數是Class, 稍後再定義這個變數
如果真正要使用到這個Class的方法(method)和資料成員(field), 還是必須import "AnotherClass.h"進來


Class Instantiation (實例化)

MyClass *myClass = [MyClass alloc];

在Objective-C 當你宣告物件時, 必須在變數名稱前加上 * 星號

如果是primitive type(float, int, CGRect, NSInteger)則不用。

CGRect frame;  //--CGRect is a structure--
int number;    //--int is a primitive type--
NSString *str; //--NSString is a class

你也可以用 id type來宣告變數, id type代表這變數可以指定為任何類型(type)或是物件(object)

id myClass = [MyClass alloc];
id str;

Field (物件資料成員)

#import <Foundation/Foundation.h>

@class AnotherClass;

@interface MyClass : NSObject {
  AnotherClass *anotherClass;
  float rate;
  NSString *data;
}

@end

Access Privileges (存取權限)

所有物件資料成員 fields的預設權限都為 @protected

• @private  -- visible only to the class that declare it (只能在宣告的class中存取)
• @public -- visible to all classes (所有classes都能存取)
• @protected -- visible to the class that declares it as well as to inheriting classes(能在宣告的class和繼承的class中存取)

#import <Foundation/Foundation.h>

@interface MyClass : NSObject {

@public
  float rate;
  NSString *name;
}

@end

可以直接在外部Class存取設成@public的這兩個變數

MyClass *myClass = [myClass alloc];
myclass->rate = 5;
myClass->name = @"Hank Wang";

Reference

Beginning-iOS-4-Application-Development
The Objective-C Programming Language: Defining a Class