使用 roslyn 獲取屬性參數

Question

我嘗試使用 Roslyn 獲取MyAttribute的命名參數。

var sourceCode = (@"
    public class MyAttribute : Attribute
    {
        public string Test { get; set; }
    }

    [MyAttribute(Test = ""Hello"")]
    public class MyClass { }
");

var syntaxTree = CSharpSyntaxTree.ParseText(sourceCode);
var mscorlib = MetadataReference.CreateFromFile(typeof(object).Assembly.Location);
var compilation = CSharpCompilation.Create("MyCompilation", new[] { syntaxTree }, new[] { mscorlib });
var semanticModel = compilation.GetSemanticModel(syntaxTree);

var syntaxRoot = syntaxTree.GetRoot();
var classNode = syntaxRoot.DescendantNodes().OfType<ClassDeclarationSyntax>().Skip(1).First();
var classModel = (ITypeSymbol)semanticModel.GetDeclaredSymbol(classNode);
var firstAttribute = classModel.GetAttributes().First();

但是firstAttribute.AttributeClass.Kind等於ErrorType ，因此firstAttribute.NamedArguments包含任何元素。

代碼不是分析器，也不是我有更完整上下文的東西，比如解決方案。

我看不出 roslyn 缺少任何參考資料或其他內容。 我該怎么做才能全面分析屬性？

Answer 1

您需要完全限定Attribute類型名稱：

var sourceCode = (@"
    public class MyAttribute : System.Attribute // < here
    {
        public string Test { get; set; }
    }

    [MyAttribute(Test = ""Hello"")]
    public class MyClass { }
");

然后它將按預期工作：

var firstNamedArg = firstAttribute.NamedArguments[0];
var key = firstNamedArg.Key; // "Test"
var value = firstNamedArg.Value.Value; // "Hello"

或者，您可以using System;添加using System; 在頂部：

var sourceCode = (@"
    using System;
    public class MyAttribute : Attribute
    {
        public string Test { get; set; }
    }

    [MyAttribute(Test = ""Hello"")]
    public class MyClass { }
");

Answer 2

您可以使用語法API來獲取atttribute的參數信息，而不是使用Roslyn的SemanticModel ：

        var firstAttribute = classNode.AttributeLists.First().Attributes.First();
        var attributeName = firstAttribute.Name.NormalizeWhitespace().ToFullString();
        Console.WriteLine(attributeName);
        // prints --> "MyAttribute"

        var firstArgument = firstAttribute.ArgumentList.Arguments.First();

        var argumentFullString = firstArgument.NormalizeWhitespace().ToFullString();
        Console.WriteLine(argumentFullString);
        // prints --> Test = "Hello"

        var argumentName = firstArgument.NameEquals.Name.Identifier.ValueText;
        Console.WriteLine(argumentName);
        // prints --> Test

        var argumentExpression = firstArgument.Expression.NormalizeWhitespace().ToFullString();
        Console.WriteLine(argumentExpression);
        // prints --> "Hello"

Answer 3

一旦你有你的xxxDeclaredSymbol你就可以得到所有的屬性

var attributes = methodSymbol.GetAttributes().ToArray();

然后，您可以遍歷數組中的每個AttributeData並使用我編寫的這個擴展，它將為您提供所有名稱+ 傳遞給屬性構造函數的值的列表，無論它們是否已命名...

// Used as a 3 value tuple for Name + TypeName + actual value
public class NameTypeAndValue
{
    public string Name { get; private set; }
    public string TypeFullName { get; private set; }
    public object Value { get; private set; }

    public NameTypeAndValue(string name, string typeFullName, object value)
    {
        Name = name;
        TypeFullName = typeFullName;
        Value = value;
    }
}

public static class ITypeSymbolExtensions
{
    // Converts names like `string` to `System.String`
    public static string GetTypeFullName(this ITypeSymbol typeSymbol) =>
        typeSymbol.SpecialType == SpecialType.None
        ? typeSymbol.ToDisplayString()
        : typeSymbol.SpecialType.ToString().Replace("_", ".");
}

public static bool TryGetAttributeAndValues(
    this AttributeData attributeData,
    string attributeFullName,
    SemanticModel model,
    out IEnumerable<NameTypeAndValue> attributeValues)
{
    var attributeValuesList = new List<NameTypeAndValue>();
    var constructorParams = attributeData.AttributeConstructor.Parameters;

    // Start with an indexed list of names for mandatory args
    var argumentNames = constructorParams.Select(x => x.Name).ToArray();

    var allArguments = attributeData.ConstructorArguments
        // For unnamed args, we get the name from the array we just made
        .Select((info, index) => new KeyValuePair<string, TypedConstant>(argumentNames[index], info))
        // Then we use name + value from the named values
        .Union(attributeData.NamedArguments.Select(x => new KeyValuePair<string, TypedConstant>(x.Key, x.Value)))
        .Distinct();

    foreach(var argument in allArguments)
    {
        attributeValuesList.Add(
            new NameTypeAndValue(
                name: argument.Key,
                typeFullName: argument.Value.Type.GetTypeFullName(),
                value: argument.Value.Value));
    }
    attributeValues = attributeValuesList.ToArray();
    return true;
}