c# - Visual Studio 2015 和 IFormatProvider 中的字符串插值 (CA1305)

Question

Visual Studio 2015 中新的字符串插值样式是这样的:

Dim s = $"Hello {name}"

但如果我使用它，代码分析会告诉我我破坏了 CA1305: Specify IFormatProvider

以前我是这样做的:

Dim s = String.Format(Globalization.CultureInfo.InvariantCulture, "Hello {0}", name)

但是新样式怎么办呢？

我必须提到我正在寻找 .Net 4.5.2 的解决方案(for .Net 4.6 dcastro has the answer)

Answer 1

您将使用 System.FormattableString 或 System.IFormattable 类:

IFormattable ifs = (IFormattable)$"Hello, {name}";
System.FormattableString fss = $"Hello, {name}";

// pass null to use the format as it was used upon initialization above.
string ifresult = ifs.ToString(null, CultureInfo.InvariantCulture);
string fsresult = fss.ToString(CultureInfo.InvariantCulture);

您需要针对 Framework 4.6 进行编译，因为 IFormattable 和 FormattableString 是旧版本中不存在的类。因此，如果您的目标是较旧版本的 .NET 框架，则无法在不触发错误的情况下使用插值语法。

除非你应用一些技巧( adapted to compile against 4.6 RTM from Jon Skeet's gist 和 forked to my own account )。只需将一个类文件添加到您的项目中，其中包含:

Update

There is now also a Nuget package available that will provide the same functionality to your project (thanks for bringing this to my attention @habakuk).

install-package StringInterpolationBridge

或者，如果您想在不向产品添加额外组件的情况下实现相同的目的，请将以下代码添加到您的项目中:

namespace System.Runtime.CompilerServices
{
    internal class FormattableStringFactory
    {
        public static FormattableString Create(string messageFormat, params object[] args)
        {
            return new FormattableString(messageFormat, args);
        }
    }
}

namespace System
{
    internal class FormattableString : IFormattable
    {
        private readonly string messageFormat;
        private readonly object[] args;

        public FormattableString(string messageFormat, object[] args)
        {
            this.messageFormat = messageFormat;
            this.args = args;
        }

        public override string ToString()
        {
            return string.Format(messageFormat, args);
        }

        public string ToString(string format, IFormatProvider formatProvider)
        {
            return string.Format(formatProvider, format ?? messageFormat, args);
        }

        public string ToString(IFormatProvider formatProvider)
        {
            return string.Format(formatProvider, messageFormat, args);
        }
    }
}

参见:

• https://msdn.microsoft.com/en-us/library/dn961160.aspx