• 什么事.pch文件?

File > New > File > iOS > Other > PCH File

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*设置pch 文件名为： projectName-Prefix.pch

*设置pch 文件内容

//
// Prefix header
//
// The contents of this file are implicitly
// included at the beginning of every source file
//

#import <Availability.h>

#ifndef __IPHONE_5_0
#warning "This project uses features only available in iOS SDK 5.0 and later."
#endif

#ifdef __OBJC__
   #import <UIKit/UIKit.h>
   #import <Foundation/Foundation.h>
#endif

• Project > Build Settings > Search for “Prefix Header“

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6.) 输入：$(SRCROOT)/YourProject-Prefix.pch
7.) Clean 并且 build你的工程