Objective，objectivec

Objective，objectivec

 

Objective - c   Chapter 1  Hello world    

1.1

1.2.On the Welcome screen, click "Create a new Xcode project" (see Figure 2-1), or just choose
File ->New ->New Project.

 

1.3.在main裡寫如下代碼

 

#import <Foundation/Foundation.h>int main(int argc, const char * argv[]) {    @autoreleasepool {        // insert code here...        NSLog(@"Hello, World!");    }    return 0;}

　

Build and run the program by clicking the Run button or pressing ⌘R.

Open the Xcode console window (by selecting View Debug Area Activate Console or pressing ⌘⇧C), which displays your program's output,

 

 

 

Now Let's pull it apart and see how it works .

 

1.4.1

#import

#import <Foundation/Foundation.h>

#import guarantees that a header file will be included only once, no matter how many times the #import directive is actually seen for that file.

#import 保證標頭檔只能被包含一次，不論#import 引入多少次這個檔案。

 

1.4.2 

Introducing Frameworks

A framework is a collection of parts—header files, libraries, images, sounds, and more—collected together into a single unit.

一個架構套件含了標頭檔，庫，圖片，聲音甚至更多到一個單元中。

The header files for the Foundation framework take up nearly a megabyte of disk storage and contain more than 14,000 lines of code, spread across over a hundred files. When you include the master header file with #import <Foundation/Foundation.h>, you get that whole vast collection.

 

Xcode is smart: it speeds up the task by using precompiled headers, a compressed and digested form of the header that's loaded quickly when you #import it.

Xcode 很聰明： 它使用先行編譯標頭檔，壓縮

1.4.3 

NSLog and @"Strings " 

NSLog (@"Hello, Objective-C!");

 

The NS Prefix: A Prescription Against Name Collisions

NS首碼： 預防名字衝突。

Rather than break compatibility with code already written for NextSTEP, Apple just continued to use the "NS" prefix. It's a historical curiosity now, like your appendix.

曆史原因，原來NestStep的縮寫NS。所以一直這麼簡寫了。

1.4.4

NSString: Where it's @

 

A string in double quotes preceded by an at sign means that the quoted string should be treated as a Cocoa NSString element.

一個在雙引號前加at 符號@ 意思是說被引用的字串應該視為cocoa NSSting 元素。

an NSString is a sequence of characters in Cocoa.

一個NSstring是一些列在cocoa中得字元。

NSString elements have a huge number of features packed into them and are used by Cocoa any time a string is needed. Here are just a few of the things an NSString can do:

   Tell you its length
   Compare itself to another string
   Convert itself to an integer or floating-point value

 

You can tell Xcode to always treat warnings as  errors . 

設定xcode使得對待警告如同錯誤。

 

 

 

1.5 Are you the  boolean type ?

Many languages have a Boolean type, which is, of course, a fancy term for variables that store true and false values. Objective-C is no exception.

oc 也有Boolean 類型。

類型是Bool 。