Xamarin.Forms + Xamarin.ios Entityframework Core 2.1.1 生成错误

Question

我正在使用Xamarin.ios应用程序使用Microsoft.EntityframeworkCore.Sqlite版本2.1.1与Xamarin.forms。网络标准2.0版本。我无法在iPhone上构建应用程序，出现以下错误：

MTOUCH：错误 MT3001：无法对程序集"project_name/iOS/obj/iPhone/Debug/device-builds/iphone10.2-11.0.2/mtouch-cache/Build/Microsoft.EntityFrameworkCore.dll"(MT3001((project_name.iOS(

任何人都可以帮助我解决错误，我试图将实体框架版本降级到 2.0.0，并将 Microsoft.extension.* 版本降级到 2.0.0。

链接器行为：不链接/仅链接SDK SDK 版本：11.0

Answer 1

我在我正在处理的项目中实现EntityFrameworkCore时遇到了类似的错误。对我来说，解决方案是将文件添加到我的iOS项目中，并包含这些内容。另外，我目前正在运行Microsoft.EntityFrameworkCore.Sqlite版本2.0.2，没有任何问题。

<?xml version="1.0" encoding="utf-8" ?>
<linker>
<!-- LinkDescription.xml. File added to iOS project by @cwrea for adaptation to EF Core.
Prevents runtime errors when reflection is used for certain types that are not otherwise referenced
directly in the project, and that would be removed by the Xamarin linker.
These kinds of runtime errors do occur in particular when using Entity Framework Core on iOS. EF Core's
query parser does reference certain .NET methods _only_ via reflection, and it is those reflection-only
instances that we need to guard against by ensuring the linker includes them. For the curious, search
for mentions of "GetRuntimeMethod" at https://github.com/aspnet/EntityFramework. Use of EF Core more
advanced than this sample may require additional types/methods added to those below.
Include the following in the project build settings under "Additional mtouch arguments":
[hyphen][hyphen]xml=${ProjectDir}/LinkDescription.xml
There is supposed to be a "LinkDescription" build action for this linker config file so the step above
shouldn't be necessary, but at time of writing Visual Studio 2017 for PC doesn't show that build action
in iOS projects, even though it is an option within iOS projects on Visual Studio 2017 for Mac.
-->
<assembly fullname="mscorlib">
<type fullname="System.String">
<method name="Compare"></method>
<method name="CompareTo"></method>
<method name="ToUpper"></method>
<method name="ToLower"></method>
</type>
</assembly>
<assembly fullname="System.Core">
<type fullname="System.Linq.Expressions.Expression`1"></type>
<type fullname="System.Linq.Queryable"></type>
</assembly>
</linker>

您还需要将该文件Build Action设置为链接描述。此外，您无需将该文件复制到输出目录。它仅在构建期间使用。

在iOS项目的项目设置中，您需要将--xml=${ProjectDir}/LinkDescription.xml放在iOS Build的Additional mtouch arguments部分中。

希望这有帮助！