If you're building from Unity3D 5 and also using a Prime31 plugin and you're getting this error it's probably due to a duplicate .dll. If you look through your warnings in Unity's editor one of them will tell you this and warn that it could cause build errors. To see if this is the case, type P31 in your project search field and it should pop right up, maybe even more than one. The duplicate's will have a ' 1' at the end of the file name. This is probably caused from updating the plugin in editor via the store or the Prime31 menu tab.

在我的例子中，我添加了一个必须使用Objective c++的框架。我找到了这个帖子:

XCode .m vs. mm

这说明了主要的。M需要重命名为main。mm，这样objective - c++类也可以被编译。

这为我解决了问题。

另一个可能导致“未定义符号”链接错误的原因是试图从.mm文件调用C函数。在这种情况下，您需要使用extern“C”{…}当您导入头文件时。

从objective - c++调用C-Function链接器错误

如果您在释放模式下构建您的Flutter项目时遇到了这个问题-这对我有帮助:

Set your build system to New Build System in File > Project Settings… delete folders ios and build_ios from your project folder. create ios module by executing flutter create . from your project folder. open Xcode and: set the IOS Deployment Target to at least 9.0 in PROJECT > Runner check your Signing & Capabilities make sure your Build Configuration is set to Release in Edit Scheme... and build for Generic iOS Device execute pod install from your project folder execute flutter pub get from your project folder

现在打开你的Xcode并构建或存档它:Product > build(或archive)

目标中可能缺少一些类。这通常发生在你重命名/删除/添加新的类文件到你的项目。若要修复，请将新添加的类添加到某些目标。

在Project Navigator中选择类(右侧栏)，打开Utilities侧栏(右侧栏)，从Utilities中选择File Inspector (File like icon)，在Target Membership选项卡下勾选你的目标。这都是为了避免“删除引用”，并再次添加“添加到目标”的技巧。

所以:选择Class -> Utilities (File Inspector) -> Target Membership ->勾选你想要的目标。

我有这个警告，当在另一个类的.h文件中写两个类时，但忘记在.m文件中写这个类的实现。