我正在尝试将Vungle广告网络应用到我的应用中。我按照文档here进行了操作。当我构建并运行时，它失败了：
Undefined symbols for architecture i386:
"_OBJC_CLASS_$_SKStoreProductViewController", referenced from:
objc-class-ref in libvunglepub.a(UIViewController+VGAppStoreViewController.o)
"_SKStoreProductParameterITunesItemIdentifier", referenced from:
-[UIViewController(VGAppStoreViewController) prepareStoreViewController:] in libvunglepub.a(UIViewController+VGAppStoreViewController.o)
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)
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