Objective-C iOS Development for Legacy & Enterprise Apps · 课时

类、对象与方法

学习定义类、创建对象，并实现实例方法和类方法来封装行为。

类、对象与方法 是 CoddyKit 上的免费 Objective-C iOS Development for Legacy & Enterprise Apps 课时。这是第 1 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 Objective-C iOS Development for Legacy & Enterprise Apps 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Objective-C iOS Development for Legacy & Enterprise Apps 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

OOP Basics: Classes & Objects

Welcome to Object-Oriented Programming (OOP) in Objective-C! OOP helps organize code into reusable blueprints called classes.

From these blueprints, we create individual items called objects. Think of a class as a cookie cutter, and an object as a cookie!

Your First Class: Header File

Every Objective-C class has two main files: a .h (header) and a .m (implementation) file.

The header file (.h) declares what your class is and what it can do. It's like the public blueprint.

Here's how to declare a simple Person class:

// Person.h
#import <Foundation/Foundation.h>

@interface Person : NSObject

// Method declaration
- (void)sayHello;

@end

Class Implementation: Source File

The implementation file (.m) contains the actual code that makes your class work. It defines the behavior declared in the header.

Here, we implement the sayHello method for our Person class:

// Person.m
#import "Person.h"

@implementation Person

- (void)sayHello {
  NSLog(@"Hello from a Person object!");
}

@end

Bringing Classes to Life: Objects

Now that we have a Person class, let's create an object from it! Creating an object is also called instantiation.

In Objective-C, we use the alloc and init methods to create new objects. alloc reserves memory, and init initializes it.

Try running this example:

#import <Foundation/Foundation.h>

// Person.h (declared here for runnable example)
@interface Person : NSObject
- (void)sayHello;
@end

// Person.m (implemented here for runnable example)
@implementation Person
- (void)sayHello {
  NSLog(@"Hello from a Person object!");
}
@end

int main(int argc, const char * argv[]) {
  @autoreleasepool {
    // Create a Person object
    Person *person1 = [[Person alloc] init];
    NSLog(@"Created a Person object: %@", person1);
  }
  return 0;
}

Instance Methods: Object Actions

Instance methods are actions that an individual object can perform. They usually work with data specific to that object.

To tell an object to perform an action, you send it a message. The syntax is [object methodName];.

Let's make our person1 object say hello:

#import <Foundation/Foundation.h>

@interface Person : NSObject
- (void)sayHello;
@end

@implementation Person
- (void)sayHello {
  NSLog(@"Hello from a Person object!");
}
@end

int main(int argc, const char * argv[]) {
  @autoreleasepool {
    Person *person1 = [[Person alloc] init];
    [person1 sayHello]; // Sending the 'sayHello' message
  }
  return 0;
}

Methods with Arguments

Methods can also take arguments (or parameters) to customize their behavior. Objective-C uses a unique syntax for method arguments, making methods very descriptive.

The first argument is part of the method name, and subsequent arguments are labeled.

Let's add a method to our Person class that takes a name:

#import <Foundation/Foundation.h>

@interface Person : NSObject
- (void)sayHelloTo:(NSString *)name; // Method with one argument
@end

@implementation Person
- (void)sayHelloTo:(NSString *)name {
  NSLog(@"Hello, %@ from a Person object!", name);
}
@end

int main(int argc, const char * argv[]) {
  @autoreleasepool {
    Person *person1 = [[Person alloc] init];
    [person1 sayHelloTo:@"Alice"]; // Sending message with argument
  }
  return 0;
}

Class Methods: Type Actions

Unlike instance methods, class methods (also known as static methods) belong to the class itself, not to a specific object.

They start with a + sign in their declaration and implementation. You call them directly on the class name, like [ClassName methodName];.

Class methods are often used for creating objects or utility functions related to the class.

#import <Foundation/Foundation.h>

@interface Person : NSObject
+ (void)aboutThisClass; // Class method declaration
@end

@implementation Person
+ (void)aboutThisClass {
  NSLog(@"This is the Person class, used to create person objects.");
}
@end

int main(int argc, const char * argv[]) {
  @autoreleasepool {
    [Person aboutThisClass]; // Calling a class method
  }
  return 0;
}

Class vs. Instance: Key Difference

Here's a quick summary of the main differences:

Instance Methods (-): Operate on a specific object's data. You need an object instance to call them.
Class Methods (+): Operate on the class itself, not an instance. You call them directly on the class name. They don't have access to instance variables.

Choose the right type based on whether the action needs specific object data or general class-related functionality.

Sending Messages in Objective-C

In Objective-C, calling a method is formally called sending a message to an object (or class).

The syntax [receiver messageName:argument]; means we're sending the messageName: message to the receiver object (or class).

This message-sending mechanism is a core part of Objective-C's dynamic nature.

Quick Check: Classes & Methods

Test your knowledge of Objective-C OOP fundamentals.

Recap: Classes, Objects & Methods

Great job! In this lesson, you learned:

What classes are (blueprints) and objects are (instances).
How to declare a class in a .h file and implement it in a .m file.
How to create objects using alloc and init.
The difference between instance methods (-) and class methods (+).
How Objective-C uses message sending to invoke methods.

You're now ready to build more complex, organized Objective-C applications!

常见问题解答

「类、对象与方法」课时是免费的吗？

是的 — 「类、对象与方法」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Objective-C iOS Development for Legacy & Enterprise Apps 课程的其余内容，请升级到 CoddyKit PRO。 Objective-C iOS Development for Legacy & Enterprise Apps 课程共包含 4 节课。

「类、对象与方法」这节课中我会学到什么？

学习定义类、创建对象，并实现实例方法和类方法来封装行为。你通过在浏览器中直接运行的动手代码来练习 Objective-C iOS Development for Legacy & Enterprise Apps，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Objective-C iOS Development for Legacy & Enterprise Apps 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Objective-C iOS Development for Legacy & Enterprise Apps 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。这是第 1 节课，共 4 节。

「类、对象与方法」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Objective-C iOS Development for Legacy & Enterprise Apps 课中编写并运行代码吗？

能。每节 Objective-C iOS Development for Legacy & Enterprise Apps 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

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