如何解决Xamarin Forms iOS错误MT5202：本机链接失败
对于我的Xamarin Forms iOS项目，我始终将“链接器行为”设置为“仅链接框架SDK”，并且过去可以使用，但是突然我不能再使用它了。尝试编译时出现以下错误。
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,3): error : undef: _OBJC_CLASS_$_MLModelConfiguration
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,3): error : undef: _OBJC_CLASS_$_MLModel
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,3): error : undef: _OBJC_CLASS_$_MLDictionaryFeatureProvider
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,3): error : undef: _OBJC_CLASS_$_MLFeatureValue
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,3): error : undef: _OBJC_CLASS_$_MLMultiArray
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,3): error MT5211: Native linking Failed,undefined Objective-C class: MLModelConfiguration. The symbol '_OBJC_CLASS_$_MLModelConfiguration' Could not be found in any of the libraries or frameworks linked with your application.
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,undefined Objective-C class: MLModel. The symbol '_OBJC_CLASS_$_MLModel' Could not be found in any of the libraries or frameworks linked with your application.
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,undefined Objective-C class: MLDictionaryFeatureProvider. The symbol '_OBJC_CLASS_$_MLDictionaryFeatureProvider' Could not be found in any of the libraries or frameworks linked with your application.
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,undefined Objective-C class: MLFeatureValue. The symbol '_OBJC_CLASS_$_MLFeatureValue' Could not be found in any of the libraries or frameworks linked with your application.
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,undefined Objective-C class: MLMultiArray. The symbol '_OBJC_CLASS_$_MLMultiArray' Could not be found in any of the libraries or frameworks linked with your application.
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,3): warning MT5215: References to 'System' might require additional -framework=XXX or -lXXX instructions to the native linker
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,3): warning MT5215: References to 'System.Net.Security' might require additional -framework=XXX or -lXXX instructions to the native linker
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,3): warning MT5215: References to 'Kernel32' might require additional -framework=XXX or -lXXX instructions to the native linker
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,3): warning MT5215: References to 'libEGL' might require additional -framework=XXX or -lXXX instructions to the native linker
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,3): error MT5202: Native linking Failed. Please review the build log.
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(885,3): error : linker command Failed with exit code 1 (use -v to see invocation)
有人知道这意味着什么吗？当我将“链接器行为”设置为“不链接”时，项目构建就没有问题。如果此信息有帮助，我不使用Firebase。
解决方法
在将多个NuGet软件包更新到最新版本后，我遇到了这个问题。花了一段时间才找出是谁的罪魁祸首，但在我的情况下是Scandit.BarcodePicker.Xamarin;使用5.17.0.10版本时，我会得到与您相同的错误，但是使用5.16.0.10版本时，一切都会很好。
根据您的情况，可能是其他包装。如果您的项目处于版本控制之下，则可以尝试恢复为较早的提交，并查看它是否可以在此构建和运行。您可能还需要清洁溶液。
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