Xamarin.Forms + Xamarin.ios Entityframework Core 2.1.1 构建错误

Question

我正在使用 Microsoft.EntityframeworkCore.Sqlite 版本 2.1.1 和 Xamarin.forms .NetStandard 2.0 版本开发 Xamarin.ios 应用程序。我无法在 iPhone 上构建应用程序，出现以下错误：

MTOUCH：错误 MT3001：无法 AOT 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)

谁能帮我解决这个错误，我尝试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

在我正在处理的项目中实现EntityFrameworkCore 时，我遇到了类似的错误。我的解决方案是在我的 iOS 项目中添加一个文件，并拥有这些内容。另外，我目前正在运行Microsoft.EntityFrameworkCore.Sqlite 2.0.2 版，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 LinkDescription。此外，您不需要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 放入Additional mtouch arguments 部分的iOS Build。

希望这会有所帮助！