C# - 获取枚举描述 - 使用增量源生成器
<h1 id="前言">前言</h1><blockquote>
<p>C# 获取枚举描述的方法有很多, 常用的有通过 <code>DescriptionAttribute</code> 反射获取, 进阶的可以加上缓存机制, 减少反射的开销。今天我们还提供一种更加高效的方法,通过增量源生成器生成获取枚举描述的代码。这是在编译层面实现的, 无需反射, 性能更高。</p>
</blockquote>
<blockquote>
<p>本文的演示代码基于 VS2022 + .NET 8.0 + .NET Standard 2.0</p>
</blockquote>
<h1 id="1-基本反射">1. 基本反射</h1>
<blockquote>
<p>这种方法是最常用的方法, 但是反射开销比较大。</p>
</blockquote>
<pre><code class="language-csharp">public enum Color
{
Red,
Green,
Blue
}
public static string GetDescription(Color color)
{
var fieldInfo = typeof(Color).GetField(color.ToString());
var descriptionAttribute = fieldInfo.GetCustomAttribute<DescriptionAttribute>();
return descriptionAttribute?.Description;
}
</code></pre>
<h1 id="2-反射--缓存">2. 反射 + 缓存</h1>
<blockquote>
<p>缓存机制可以减少反射的开销, 避免反射过于频繁。</p>
</blockquote>
<pre><code class="language-csharp">private static readonly Dictionary<Color, string> _descriptionCache = new Dictionary<Color, string>();
public static string GetDescription(Color color)
{
if (_descriptionCache.TryGetValue(color, out var description))
{
return description;
}
var fieldInfo = typeof(Color).GetField(color.ToString());
var descriptionAttribute = fieldInfo.GetCustomAttribute<DescriptionAttribute>();
description = descriptionAttribute?.Description;
_descriptionCache.Add(color, description);
return description;
}
</code></pre>
<h1 id="3-反射--缓存--泛型类-推荐">3. 反射 + 缓存 + 泛型类 (推荐)</h1>
<blockquote>
<p>泛型可以减少代码重复。下面的代码为基本实现, 没有考虑线程安全问题。线程安全问题可以通过锁机制解决。可以使用静态构造函数初始化缓存。或者使用 ConcurrentDictionary 代替 Dictionary。或者使用 Lazy<t> 代替缓存。</t></p>
</blockquote>
<pre><code class="language-csharp">public class EnumDescription<T> where T : Enum
{
private static readonly Dictionary<T, string> _descriptionCache = new Dictionary<T, string>();
public static string GetDescription(T value)
{
if (_descriptionCache.TryGetValue(value, out var description))
{
return description;
}
var fieldInfo = typeof(T).GetField(value.ToString());
var descriptionAttribute = fieldInfo.GetCustomAttribute<DescriptionAttribute>();
description = descriptionAttribute?.Description;
_descriptionCache.Add(value, description);
return description;
}
}
</code></pre>
<h1 id="4-增量源生成器-消除反射">4. 增量源生成器 (消除反射)</h1>
<h3 id="创建增量源生成器类库项目-net-standard-20">创建增量源生成器类库项目 (.NET Standard 2.0)</h3>
<ol>
<li>
<p>创建一个基于 .NET Standard 2.0 的类库项目名为: <code>SourceGenerator</code></p>
</li>
<li>
<p>添加 NuGet 包 <code>Microsoft.CodeAnalysis.CSharp</code> 版本 <code>4.8.0</code></p>
</li>
</ol>
<pre><code class="language-csharp"><Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFramework>netstandard2.0</TargetFramework>
<LangVersion>latest</LangVersion>
<EnforceExtendedAnalyzerRules>true</EnforceExtendedAnalyzerRules>
</PropertyGroup>
<ItemGroup>
<PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.8.0" />
</ItemGroup>
</Project>
</code></pre>
<ol start="3">
<li>添加 <code>EnumDescriptionGenerator</code> 类, 实现 <code>IIncrementalGenerator</code> 接口</li>
</ol>
<pre><code class="language-csharp">using System.Linq;
using System.Text;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Text;
public class EnumDescriptionGenerator : IIncrementalGenerator
{
public void Initialize(IncrementalGeneratorInitializationContext context)
{
var enumDeclarations = context.SyntaxProvider
.CreateSyntaxProvider(
predicate: (syntaxNode, _) => syntaxNode is EnumDeclarationSyntax,
transform: (generatorSyntaxContext, _) =>
{
var enumDeclaration = (EnumDeclarationSyntax)generatorSyntaxContext.Node;
var enumSymbol = generatorSyntaxContext.SemanticModel.GetDeclaredSymbol(enumDeclaration) as INamedTypeSymbol;
return new { EnumDeclaration = enumDeclaration, EnumSymbol = enumSymbol };
})
.Where(t => t.EnumSymbol != null)
.Collect();
var compilationAndEnums = context.CompilationProvider.Combine(enumDeclarations);
context.RegisterSourceOutput(compilationAndEnums, (sourceProductionContext, tuple) =>
{
var compilation = tuple.Left;
var enums = tuple.Right;
foreach (var item in enums)
{
var enumDeclaration = item.EnumDeclaration;
var enumSymbol = item.EnumSymbol;
if (!enumSymbol.GetMembers("GetDescription").Any())
{
var source = GenerateSourceCode(enumSymbol);
sourceProductionContext.AddSource($"{enumSymbol.Name}Descriptions.g.cs", SourceText.From(source, Encoding.UTF8));
}
}
});
}
// 生成枚举描述扩展方法的代码
private static string GenerateSourceCode(INamedTypeSymbol enumSymbol)
{
var enumName = enumSymbol.Name;
var namespaceName = enumSymbol.ContainingNamespace?.ToString() ?? "Global";
var sb = new StringBuilder();
sb.AppendLine($"namespace {namespaceName};");
sb.AppendLine($"public static partial class {enumName}Extensions");
sb.AppendLine("{");
sb.AppendLine($" public static string GetDescription(this {enumName} value) =>");
sb.AppendLine(" value switch");
sb.AppendLine(" {");
// 4. 遍历枚举成员
foreach (var member in enumSymbol.GetMembers().Where(m => m.Kind == SymbolKind.Field))
{
var description = member.GetAttributes()
.FirstOrDefault(a => a.AttributeClass?.Name == "DescriptionAttribute")
?.ConstructorArguments.FirstOrDefault().Value?.ToString()
?? member.Name;
sb.AppendLine($" {enumName}.{member.Name} => \"{description}\",");
}
sb.AppendLine(" _ => string.Empty");
sb.AppendLine(" };");
sb.AppendLine("}");
return sb.ToString();
}
}
</code></pre>
<h3 id="创建控制台主项目-mainproject">创建控制台主项目 <code>MainProject</code></h3>
<ol>
<li>使用 .NET 8.0 , 引用 <code>SourceGenerator</code> 项目, 注意引用方式如下:</li>
</ol>
<pre><code class="language-csharp"><Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net8.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
</PropertyGroup>
<ItemGroup>
<ProjectReference Include="..\SourceGenerator\SourceGenerator.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" />
</ItemGroup>
</Project>
</code></pre>
<ol start="2">
<li>在 <code>MainProject</code> 中使用生成的枚举描述扩展方法</li>
</ol>
<pre><code class="language-csharp">namespace MainProject;
class Program
{
static void Main()
{
foreach (var color in Enum.GetValues<Color>())
{
Console.WriteLine(color.GetDescription());
}
Console.ReadKey();
}
}
</code></pre>
<ol start="3">
<li>编译运行, 编译器会自动生成枚举描述扩展方法的代码。</li>
</ol>
<h1 id="演示程序截图">演示程序截图:</h1>
<p><img src="https://img2024.cnblogs.com/blog/776421/202503/776421-20250322163840591-441405763.png" alt="image" loading="lazy"></p>
<p><img src="https://img2024.cnblogs.com/blog/776421/202503/776421-20250322164350209-1779171688.png" alt="image" loading="lazy"></p>
<h1 id="总结">总结</h1>
<p>通过增量源生成器, 我们可以在编译期自动生成获取枚举描述的代码, 无需反射, 性能更高。</p><br><br>
来源：https://www.cnblogs.com/broadm/p/18786843
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