c# - Error.ArgumentNull() 在哪里/什么？

Question

有时我会在代码示例中看到这一点：

throw Error.ArgumentNull("someParameter");

这里有一个例子，在第 89 行。

我想Error在我自己的代码中使用。我在哪里可以找到它？

（我试图自己找到它，我尝试using了该文件顶部的命名空间，并试图让 Visual Studio 找到它，但到目前为止没有运气。）

Answer 1

它是由库的创建者定义的帮助器类，以使他们的生活更轻松。

错误.cs文件：

internal static ArgumentNullException ArgumentNull(string parameterName, string messageFormat, params object[] messageArgs)
{
    return new ArgumentNullException(parameterName, Error.Format(messageFormat, messageArgs));
}

---

如果您正在寻找类似的功能，请查看Code Contracts（适用于 Visual Studio 的非 Express 版本）。然后你可以写这样的东西：

using System.Diagnostics.Contracts;

void MyMethod(string someParameter)
{
    Contract.Requires<ArgumentNullException>(someParameter != null);

    // ...
}

...and it will throw an exception at run-time when this condition has not been met.

Answer 2

It is an internal helper class, with internal visibility. That's why you haven't been able to locate it.

Microsoft source code uses this pattern in a variety of places.

But why do it? It enables you to throw a consistent, nicely-formatted, localized exception without having to put that logic in every exception handler.

Taking that a step further, some definitions even contain compiler directives, such as:

        internal static ArgumentException InvalidEnumArgument( string parameterName, int invalidValue, Type enumClass ) {
#if NETFX_CORE
            return new ArgumentException(Error.Format(CommonWebApiResources.InvalidEnumArgument, parameterName, invalidValue, enumClass.Name), parameterName);
#else
            return new InvalidEnumArgumentException( parameterName, invalidValue, enumClass );
#endif
        }

Other methods (such as PropertyNull()) are decorated with code analysis suppression messages.

Again, it's simply a convenience/consistency mechanism to avoid repeating this code all over the place.

I probably wouldn't suggest trying to use this exact code in your own project, because your needs will be different. But you can certainly use it as a pattern.

Answer 3

那是一个自定义的内部类型，它在 BCL 中不存在。

namespace System.Web.Http
{
    /// <summary>
    /// Utility class for creating and unwrapping <see cref="Exception"/> instances.
    /// </summary>
    internal static class Error
    {}
 }

你可以从那里复制它，如果你愿意的话。