Objective-C知识总结（抄）

暗夜 posted @ 2010年11月11日 19:51 in 未分类 , 1728 阅读

刚刚使用Objective-C 写了一个面向对象的程序，现在将一些知识点归结如下：

1）Objective-C的类定义包含两个部分，一是类接口的声明，二是类方法的实现。
2）所有的 Objective-C的所有编译指示都以@打头。
a)类接口以@interface开始以@end结束。
b)类的实现以@implementation开始以@end结束。
c)每个实现文件必须包含它自己对应的接口文件，这样实现文件中就可以安全的将父类名删除，将类的 instance变量声明删除，只关注类的方法的实现；可以这样做的原因是我们没有必要重复接口文件中同样的声明。
d)不要将源文件中的函数参数命名成与该类成员变量同名的变量，否则函数的参数名会覆盖类的成员变量，导致在该函数的实现中看不到类定义中的成员变量。
如在头文件中一个类接口声明如下：


@interface Circle:NSObject
{
ShapeRect bounds;
ShapeColor fillColor;
}
- (void) SetFillColor: (ShapeColor) fillColor;
- (void) SetBounds: (ShapeRect) bounds;
- (void) draw;
@end //Circle

我们源文件中类的实现如下：

@implementation Circle

- (void) SetFillColor: (ShapeColor)c
{
fillColor = c;
}

- (void) SetBounds: (ShapeRect)b
{
bounds = b;
}

- (void) draw
{
NSLog(@"drawing a circle at (%d,%d,%d,%d) in %@",bounds.x,bounds.y,bounds.width,bounds.hight,colorName(fillColor));
}
@end //circle

3）id 比较独特，在Objective-C中它是一种泛型，该类型的变量可以存储指向任何一个对象的指针。

4）向一个对象发送一个消息，那么该对象又是如何去执行该消息所对应的代码呢？
每个对象都包含一个指向其类的指针，而类也包含一个指针该指针指向该类的代码区域。
这样当对象收到一个消息，对象通过其包含的指向找到其所属的类对象，通过类对象的代码区指针又可以找到与消息对应的函数。
每个对象都包含一个名叫isa的指针，就是该指针指向类。

5）Objective-C中的基本术语：
类：类是一种结构，它用于表示一个对象的类型。对象通过isa指针来引用类来获得与本身有关的所有信息，尤其是像4）中所说的如何执行每种操作的代码。

对象：也是一种结构，该结构主要包含成员变量的值和指向其类的隐藏指针（isa）；同一类的所有象共享一份代码。

实例：是“对象”的另外一种称呼。
消息：是对象可以执行的操作，用于通知对象去做什么，一个对象能响应哪些消息可以从接口定义中知道。
方法：为响应消息而运行的代码。根据对象的类，消息可以调用不同的方法。
接口：是对对象的类应该提供的特性的描述。相当于是告诉其他使用该类的客户，该类的对象可以接收哪几个消息。与上面说的“消息”术语一致。
实现：是使接口正常工作的代码，也就是使对象消息正常工作的代码。与上面的“实现”术语一致。

6）有些方法名后有冒号，有些没有呢？如何判断什么时候有，什么时候没有？
如果方法使用参数，则需要冒号；否则不需要冒号。如上面的代码片断。

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