以下代码用于复制我尝试在新的ASP.NET Core 3.0 API项目中创建的一些扩展名出错的情况。
using ClassLibrary1;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;
namespace WebApplication1
{
public class Program
{
public static void Main(string[] args)
{
CreateHostBuilder(args).Build().Run();
}
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseStartup<Startup>();
webBuilder.ConfigureAppConfiguration((context, config) =>
{
// this works fine
var env = context.HostingEnvironment;
});
webBuilder.CustomConfigureAppConfiguration();
})
.ConfigureAppConfiguration((context, config) =>
{
// this works fine
var env = context.HostingEnvironment;
})
.CustomConfigureAppConfiguration();
}
}
Extensions
类需要位于不同的项目中。当在同一主项目中时似乎可以正常工作。
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;
// This project can be either netstandard2.0 or netcoreapp3.0
namespace ClassLibrary1
{
public static class Extensions
{
public static IWebHostBuilder CustomConfigureAppConfiguration(this IWebHostBuilder hostBuilder)
{
hostBuilder.ConfigureAppConfiguration((context, config) =>
{
// this fails with System.MissingMethodException: 'Method not found: 'Microsoft.AspNetCore.Hosting.IHostingEnvironment Microsoft.AspNetCore.Hosting.WebHostBuilderContext.get_HostingEnvironment()'.'
var env = context.HostingEnvironment;
});
return hostBuilder;
}
public static IHostBuilder CustomConfigureAppConfiguration(this IHostBuilder hostBuilder)
{
hostBuilder.ConfigureAppConfiguration((context, config) =>
{
// this fails with System.MissingMethodException: 'Method not found: 'Microsoft.Extensions.Hosting.IHostingEnvironment Microsoft.Extensions.Hosting.HostBuilderContext.get_HostingEnvironment()'.'
var env = context.HostingEnvironment;
});
return hostBuilder;
}
}
}
只有在运行时访问HostingEnvironment
时才会出现故障。当删除/注释var env = context.HostingEnvironment;
赋值时,我仍然可以在调试中检查和查看它。
你知道我在这里缺少什么吗?
编辑
将ClassLibrary1
项目更新到netcoreapp3.0
并像下面添加<FrameworkReference Include="Microsoft.AspNetCore.App" />
即可解决:
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFramework>netcoreapp3.0</TargetFramework>
</PropertyGroup>
<ItemGroup>
<FrameworkReference Include="Microsoft.AspNetCore.App" />
<PackageReference Include="Microsoft.AspNetCore.Hosting.Abstractions" Version="2.2.0" />
</ItemGroup>
</Project>
如果可能的话,我仍然希望将项目保持为netstandard2.0
。也许需要一些特定的NuGet包吗?