参数列表语法

Question

我试图理解这样的结构：

  - (void)someMethodWithArgs:(type?) param, ...
{
        ???
}

[self someMethodWithArgs:arg1, arg2, arg3];

• 如何访问参数列表？
• 应该'type'是指针，还是'int'，例如？

Answer 1

Objective-C功能的工作方式。

声明

- (void) someMethodWithArgA:(type)paramName argB:(typeB)paramNameB
{
     // do something with paramName and paramNameB 

}

<强>调用

[self someMethodWithArgA:val argB:valB];

---

C等价物将是：

void someMethodWithArgs(type paramName, typeB paramNameB)
{
     // do something with paramName and paramNameB    
}

someMethodWithArgs(val,valB);

---

当然，和C一样，变量类型可以是任何（为什么它们只是指针？）。

---

一个简单的例子：

- (int)addNum:(int)a withNum:(int)b
{
      int c = a+b;
      return c;
}

int k = [self addNum:2 withNum:3];
// k = 5

---

参考

  

面向对象编程的Objective-C模型基于   消息传递给对象实例。在Objective-C中，没有   简单地调用一个方法;一个人发送消息。

http://en.wikipedia.org/wiki/Objective-C#Messages

---

的更新

使用可变数量的参数实现方法

#import <Cocoa/Cocoa.h>

@interface NSMutableArray (variadicMethodExample)

- (void) appendObjects:(id) firstObject, ...; // This method takes a nil-terminated list of objects.

@end

@implementation NSMutableArray (variadicMethodExample)

- (void) appendObjects:(id) firstObject, ...
{
     id eachObject;
     va_list argumentList;
     if (firstObject) // The first argument isn't part of the varargs list,
     {                                   // so we'll handle it separately.
          [self addObject: firstObject];
          va_start(argumentList, firstObject); 
          // Start scanning for arguments after firstObject.

          // As many times as we can get an argument of type "id"
          while (eachObject = va_arg(argumentList, id)) 
                 [self addObject: eachObject]; 

          va_end(argumentList);
     }
}

@end

来自：http://developer.apple.com/library/mac/#qa/qa1405/_index.html

Answer 2

在ObjC中，参数列表语法产生C参数列表语法。

- (void) appendObjects:(id) firstObject, ...
{
id eachObject;
va_list argumentList;
va_start(argumentList, firstObject); // Start scanning for arguments after firstObject.
while (eachObject = va_arg(argumentList, id)) // As many times as we can get an argument of type "id"
  [self addObject: eachObject]; // that isn't nil, add it to self's contents.
va_end(argumentList);
}

您可以在此处找到更多信息：developer.apple.com

更新：ooops，我有点晚了：）

Answer 3

Matt Gallagher提供了一个关于变量参数列表的精彩教程：

Variable argument lists in Cocoa

在Apple的文档中，还有一篇关于此主题的简短技术Q＆amp; A QA1405：

Variable arguments in Objective-C methods