OC静态库里NSClassFromString得到nil的解决

如果你在静态库中有从类名反射回类的代码, 如下:

NSString *myClassStr = @"myClass";  
Class myClazz = NSClassFromString(myClassStr);  
if (myClazz) {  
    id myClassInit = [[myClazz alloc] init];  
}

有时候(经常)会出现得到了Class为nil的情况, 网上搜索, 一般是这么说的:

The class object named by aClassName, or nil if no class by that name is currently loaded. If aClassName is nil, returns nil.

来自于64位系统的一个bug:

IMPORTANT: For 64-bit and iPhone OS applications, there is a linker bug that prevents -ObjC from loading objects files from static libraries that contain only categories and no classes. The workaround is to use the -all_load or -force_load flags. -all_load forces the linker to load all object files from every archive it sees, even those without Objective-C code. -force_load is available in Xcode 3.2 and later. It allows finer grain control of archive loading. Each -force_load option must be followed by a path to an archive, and every object file in that archive will be loaded.

就我的实测
首先, 你需要在你的主项目(的target)对build setting进行更改, 而不是静态库的项目!
其次, -all_load有效, -force_load甚至编译都过不了
最后, 结合上面, 就是在主项目(引用静态库的项目)的build setting里面搜索other linker flags, 然后把-all_load加进去就行了

OC静态库里NSClassFromString得到nil的解决

原文：http://www.cnblogs.com/walkerwang/p/4534527.html