.pch文件也是一種頭文件，它的內(nèi)容能被項(xiàng)目中的其他所有源文件共享和訪問(wèn)。是一個(gè)預(yù)編譯文件。
pch文件的作用：
1.存放一些全局的宏(整個(gè)項(xiàng)目中都用得上的宏)
2.用來(lái)包含一些頭文件(整個(gè)項(xiàng)目中都用得上的頭文件)
3.能自動(dòng)打開(kāi)或者關(guān)閉日志輸出功能
Xcode新建pch文件
Xcode配置pch文件
pch文件的簡(jiǎn)單例子
一個(gè)小項(xiàng)目的pch文件：
#ifndef PrefixHeader_pch
#define PrefixHeader_pch
// Include any system framework and library headers here that should be included in all compilation units.
// You will also need to set the Prefix Header build setting of one or more of your targets to reference this file.
#import "ARSearchBar.h"
#import <FMDB.h>
#import "ARSqliteTool.h"
#import <AFNetworking.h>
#import <SSZipArchive.h>
#import <MobileCoreServices/MobileCoreServices.h>
#import <SystemConfiguration/SystemConfiguration.h>
#define ARUserDefaults [NSUserDefaults standardUserDefaults]
#define ARScreenBounds [UIScreen mainScreen].bounds
#define ARScreenWidth [UIScreen mainScreen].bounds.size.width
#define ARScreenHeight [UIScreen mainScreen].bounds.size.height
#define WeakSelf __weak typeof(self) weakSelf = self;
/**
* 1.返回一個(gè)RGBA格式的UIColor對(duì)象
*/
#define RGBA(r, g, b, a) [UIColor colorWithRed:r/255.0f green:g/255.0f blue:b/255.0f alpha:a]
/**
* 2.返回一個(gè)RGB格式的UIColor對(duì)象
*/
#define RGB(r, g, b) RGBA(r, g, b, 1.0f)
#endif /* PrefixHeader_pch */
