c# - ReSharper 声称我的表达总是正确的？它是正确的还是错误？

Question

ReSharper 声称我对 serviceProvider 的空检查始终为真，这很奇怪。我认为 serviceProvider 很可能为空。我在这里错了吗，或者这是一个 ReSharper 错误？

public override object ProvideValue(IServiceProvider serviceProvider)
{
    switch (Mode)
    {
        case BindingMode.TwoWay:
            throw new InvalidOperationException("Invalid binding mode.");

        case BindingMode.OneWayToSource:
            throw new InvalidOperationException("Invalid binding mode.");

        case BindingMode.OneWay:
        case BindingMode.OneTime:
            break;

        case BindingMode.Default:
            if (serviceProvider != null) // Expression is always true?? O.o
            {
                // Returns something possibly...
            }

            throw new InvalidOperationException("Invalid binding mode.");

        default:
            throw new InvalidOperationException("Unexpected binding mode.");
    }

    return base.ProvideValue(serviceProvider);
}

更新:

我创建了一个控制台应用程序，下面的代码也给出了警告(来自 ReSharper)Possible null assignment to entity marked with 'NotNull' attribute.

var binding = new CustomBinding();
binding.ProvideValue(null);

Answer 1

摘自 http://msdn.microsoft.com/en-us/library/system.windows.markup.typeextension.providevalue%28v=vs.110%29.aspx 的文档

You can pass null for serviceProvider, but only if this TypeExtension instance was established with an initial true type in the constructor rather than a typeName. Otherwise, this markup extension implementation relies on services based on the passed serviceProvider. It must not be null. The serviceProvider is expected to provide a service for IXamlTypeResolver.

您还可以查看 When can a generic parameter never be null有关这方面的更多信息。

显然，如果我是正确的，这个方法的参数有一个约定 [NotNull]，因为一些实现在 null 参数上抛出错误。