Xcode6在ios7上编译framework报错

错误描述：

dyld: Symbol not found: _OBJC_CLASS_$_UIPresentationController

 Referenced from: /var/mobile/Applications/ 2296090E-900A-47DE-9D6F-972CAAE4524F/FamilySchoolPro    copy.app/FamilySchoolPro copy

 Expected in: /System/Library/Frameworks/   UIKit.framework/UIKit

in /var/mobile/Applications/2296090E-900A-47DE-9D6F-972CAAE4524F/FamilySchoolPro copy.app/FamilySchoolPro copy

错误原因：

框架（UIKit.framework）在低版本的设备上找不到，加载不上

解决方法：

Xcode6在ios7上编译framework报错

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