构建错误“您是否缺少 using 指令或程序集参考"- 目标框架版本 4 [英] Build error "Are you missing a using directive or assembly reference" - target framework version 4

问题描述

我有一个使用库的项目(来自 nuget)
我项目的目标框架目前是4.0

I've got a project that uses a library (from nuget)
The target framework for my project is currently 4.0

我正在使用库中的对象和方法，我获得了智能感知等...

I'm using objects and methods from the library, I get intellisense etc...

但是，当我构建时，编译失败

However, when I build, compilation fails with

找不到类型或命名空间.您是否缺少 using 指令或程序集引用?

The type or namespace could not be found. Are you missing a using directive or assembly reference?

如果我将项目的目标框架更改为 4.5，它会编译.

If I change the target framework of the project to 4.5, it compiles.

有没有办法解决这个问题?

Is there a way round this?

编辑

作为一个具体示例，以下是在一个特定情况下重现此问题的步骤.

As a specific example, here are the steps to reproduce this problem in one particular case.

• 文件 -> 新建项目
• 新的控制台应用程序

• 将目标框架设置为 4.0

• File -> New Project
• New Console application

• Set Target framework to 4.0

Nuget 安装 paymill 包装器

使用 Paymill 包装器中的一种类型.例如:

Use one of the types in the Paymill wrapper. For example:

using PaymillWrapper.Models;
using PaymillWrapper.Service;  

public class MyClass
{
    private readonly PaymentService _paymentService;
}

VS 没有抱怨.
编译

VS doesn't complain.
Compile

接收错误:

找不到类型或命名空间名称ClientService"(您是否缺少 using 指令或程序集引用?)

The type or namespace name 'ClientService' could not be found (are you missing a using directive or an assembly reference?)

推荐答案

答案在于构建输出:

2>C:WindowsMicrosoft.NETFrameworkv4.0.30319Microsoft.Common.targets(1605,5):警告 MSB3274:无法解析主要引用PaymillWrapper"，因为它是针对.NETFramework,Version=v4.5"框架.这是比当前目标框架.NETFramework,Version=v4.0"更高的版本.

2>C:WindowsMicrosoft.NETFrameworkv4.0.30319Microsoft.Common.targets(1605,5): warning MSB3274: The primary reference "PaymillWrapper" could not be resolved because it was built against the ".NETFramework,Version=v4.5" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.0".

2>C:WindowsMicrosoft.NETFrameworkv4.0.30319Microsoft.Common.targets(1605,5):警告 MSB3268:无法解析主要引用PaymillWrapper"，因为它具有间接依赖关系在当前目标框架中无法解决的框架程序集System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"上..NETFramework，版本 = v4.0".要解决此问题，请删除引用PaymillWrapper"或将您的应用程序重定向到包含System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"的框架版本.

2>C:WindowsMicrosoft.NETFrameworkv4.0.30319Microsoft.Common.targets(1605,5): warning MSB3268: The primary reference "PaymillWrapper" could not be resolved because it has an indirect dependency on the framework assembly "System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which could not be resolved in the currently targeted framework. ".NETFramework,Version=v4.0". To resolve this problem, either remove the reference "PaymillWrapper" or retarget your application to a framework version which contains "System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a".

换句话说，NuGet 包使用对 .NET 4.5 的引用，因此您只能在 .NET 4.5+ 项目中使用它.

In other words, the NuGet package uses a reference to .NET 4.5, so you can only use it on .NET 4.5+ projects.

您可能想询问 Paymill Wrapper 的作者，看看他们是否可以发布针对 .NET 4 的版本.

You might want to ask the authors of Paymill Wrapper to see if they could publish a version which targets .NET 4 instead.

请注意，NuGet 包页面 甚至声明了这一点:

Note that the NuGet package page even states this:

依赖
- .NETFramework 4.5

Dependencies
- .NETFramework 4.5

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