问题描述
我正在寻找一种方法来检查，如果它的类定义，进口和使用的框架之前的框架存在，和/或。具体来说，框架是资产库。
I'm looking for a way to check if a framework exists and/or if it's classes are defined, before importing and using that framework. Specifically, the framework is Assets Library.
目前，我能够与核心数据框架，要做到这一点，因为该框架有一个名为CoreDataDefines.h文件，它提供了一个preprocessor指令_COREDATADEFINES_H。这让我简单地检查了确定指标，像这样：
Currently, I'm able to do this with the Core Data framework, since that framework has a file called CoreDataDefines.h which provides a preprocessor directive _COREDATADEFINES_H. This allows me to simply check for that defintion like so:
#ifdef _COREDATADEFINES_H
#import <CoreData/CoreData.h>
// do something with Core Data
#else
// do something without using Core Data
#endif
不幸的是，资产库并没有提供一个明确的定义头文件，所以我在寻找一种方式来写我自己的#define语句，可以导入前检查框架的存在，就像我有以上核心数据完成的。
Unfortunately, the Assets Library does not provide a clear definitions header file so I'm looking for a way to write my own #define statement that can check for the framework's existence before importing it, much like I have done for Core Data above.
我已经试过这样：
#if __IPHONE_OS_VERSION_MAX_ALLOWED >= 40000
// import assets library if defined !
#define ASSETSLIBRARY_DEFINE (NSClassFromString(@"ALAsset") != nil)
#if ASSETSLIBRARY_DEFINE
#import <AssetsLibrary/AssetsLibrary.h>
#endif
#endif
...但没有运气。
编译器告诉我，令牌不在preprocessor SUBEX pression有效的二元运算符。
... but no luck.
The compiler tells me that the "Token is not a valid binary operator in a preprocessor subexpression."
任何帮助始终是多少AP preciated。
Any help is always much appreciated.
推荐答案
如果你知道你可以查阅一下类应与框架导入，如果它被加载：
If you know what class should be imported with the framework you can check if it is loaded:
BOOL isFrameworkLoaded = (NSClassFromString(@"MyClassNameFromTheFramework") != nil);
这篇关于条件编译支票框架在导入前的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！