我有一个类,它看起来像这样:

public class Field
{
    public string FieldName;
    public string FieldType;
}

和一个对象列表<字段>值:

{"EmployeeID","int"},
{"EmployeeName","String"},
{"Designation","String"}

我想创建一个类,看起来像这样:

Class DynamicClass
{
    int EmployeeID,
    String EmployeeName,
    String Designation
}

有什么办法可以做到吗?

我希望它在运行时生成。我不希望在文件系统中驻留一个物理CS文件。


当前回答

正如Hans所建议的,您可以使用Roslyn动态创建类。

完整的资料来源:

using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;

namespace RoslynDemo1
{
    class Program
    {
        static void Main(string[] args)
        {
            var fields = new List<Field>()
            {
                new Field("EmployeeID","int"),
                new Field("EmployeeName","String"),
                new Field("Designation","String")
            };

            var employeeClass = CreateClass(fields, "Employee");

            dynamic employee1 = Activator.CreateInstance(employeeClass);
            employee1.EmployeeID = 4213;
            employee1.EmployeeName = "Wendy Tailor";
            employee1.Designation = "Engineering Manager";

            dynamic employee2 = Activator.CreateInstance(employeeClass);
            employee2.EmployeeID = 3510;
            employee2.EmployeeName = "John Gibson";
            employee2.Designation = "Software Engineer";

            Console.WriteLine($"{employee1.EmployeeName}");
            Console.WriteLine($"{employee2.EmployeeName}");

            Console.WriteLine("Press any key to continue...");
            Console.ReadKey();
        }

        public static Type CreateClass(List<Field> fields, string newClassName, string newNamespace = "Magic")
        {
            var fieldsCode = fields
                                .Select(field => $"public {field.FieldType} {field.FieldName};")
                                .ToString(Environment.NewLine);

            var classCode = $@"
                using System;

                namespace {newNamespace}
                {{
                    public class {newClassName}
                    {{
                        public {newClassName}()
                        {{
                        }}

                        {fieldsCode}
                    }}
                }}
            ".Trim();

            classCode = FormatUsingRoslyn(classCode);


            var assemblies = new[]
            {
                MetadataReference.CreateFromFile(typeof(object).Assembly.Location),
            };

            /*
            var assemblies = AppDomain
                        .CurrentDomain
                        .GetAssemblies()
                        .Where(a => !string.IsNullOrEmpty(a.Location))
                        .Select(a => MetadataReference.CreateFromFile(a.Location))
                        .ToArray();
            */

            var syntaxTree = CSharpSyntaxTree.ParseText(classCode);

            var compilation = CSharpCompilation
                                .Create(newNamespace)
                                .AddSyntaxTrees(syntaxTree)
                                .AddReferences(assemblies)
                                .WithOptions(new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));

            using (var ms = new MemoryStream())
            {
                var result = compilation.Emit(ms);
                //compilation.Emit($"C:\\Temp\\{newNamespace}.dll");

                if (result.Success)
                {
                    ms.Seek(0, SeekOrigin.Begin);
                    Assembly assembly = Assembly.Load(ms.ToArray());

                    var newTypeFullName = $"{newNamespace}.{newClassName}";

                    var type = assembly.GetType(newTypeFullName);
                    return type;
                }
                else
                {
                    IEnumerable<Diagnostic> failures = result.Diagnostics.Where(diagnostic =>
                        diagnostic.IsWarningAsError ||
                        diagnostic.Severity == DiagnosticSeverity.Error);

                    foreach (Diagnostic diagnostic in failures)
                    {
                        Console.Error.WriteLine("{0}: {1}", diagnostic.Id, diagnostic.GetMessage());
                    }

                    return null;
                }
            }
        }

        public static string FormatUsingRoslyn(string csCode)
        {
            var tree = CSharpSyntaxTree.ParseText(csCode);
            var root = tree.GetRoot().NormalizeWhitespace();
            var result = root.ToFullString();
            return result;
        }
    }

    public class Field
    {
        public string FieldName;
        public string FieldType;

        public Field(string fieldName, string fieldType)
        {
            FieldName = fieldName;
            FieldType = fieldType;
        }
    }

    public static class Extensions
    {
        public static string ToString(this IEnumerable<string> list, string separator)
        {
            string result = string.Join(separator, list);
            return result;
        }
    }
}

其他回答

您还可以使用DynamicExpressions动态地创建类。

因为'Dictionary'有紧凑的初始化器并处理键冲突,所以你会想这样做。

  var list = new Dictionary<string, string> {
    {
      "EmployeeID",
      "int"
    }, {
      "EmployeeName",
      "String"
    }, {
      "Birthday",
      "DateTime"
    }
  };

或者,您可能希望使用JSON转换器将序列化的字符串对象构造为可管理的对象。

然后使用System.Linq.Dynamic;

  IEnumerable<DynamicProperty> props = list.Select(property => new DynamicProperty(property.Key, Type.GetType(property.Value))).ToList();

  Type t = DynamicExpression.CreateClass(props);

剩下的就是使用System.Reflection。

  object obj = Activator.CreateInstance(t);
  t.GetProperty("EmployeeID").SetValue(obj, 34, null);
  t.GetProperty("EmployeeName").SetValue(obj, "Albert", null);
  t.GetProperty("Birthday").SetValue(obj, new DateTime(1976, 3, 14), null);
}  

您还可以使用DynamicObject动态创建类。

public class DynamicClass : DynamicObject
{
    private Dictionary<string, KeyValuePair<Type, object>> _fields;

    public DynamicClass(List<Field> fields)
    {
        _fields = new Dictionary<string, KeyValuePair<Type, object>>();
        fields.ForEach(x => _fields.Add(x.FieldName,
            new KeyValuePair<Type, object>(x.FieldType, null)));
    }

    public override bool TrySetMember(SetMemberBinder binder, object value)
    {
        if (_fields.ContainsKey(binder.Name))
        {
            var type = _fields[binder.Name].Key;
            if (value.GetType() == type)
            {
                _fields[binder.Name] = new KeyValuePair<Type, object>(type, value);
                return true;
            }
            else throw new Exception("Value " + value + " is not of type " + type.Name);
        }
        return false;
    }

    public override bool TryGetMember(GetMemberBinder binder, out object result)
    {
        result = _fields[binder.Name].Value;
        return true;
    }
}

我将所有类字段连同它们的类型和值一起存储在字典_fields中。这两种方法都可以获取或设置一些属性的值。必须使用dynamic关键字创建该类的实例。

使用你的例子:

var fields = new List<Field>() { 
    new Field("EmployeeID", typeof(int)),
    new Field("EmployeeName", typeof(string)),
    new Field("Designation", typeof(string)) 
};

dynamic obj = new DynamicClass(fields);

//set
obj.EmployeeID = 123456;
obj.EmployeeName = "John";
obj.Designation = "Tech Lead";

obj.Age = 25;             //Exception: DynamicClass does not contain a definition for 'Age'
obj.EmployeeName = 666;   //Exception: Value 666 is not of type String

//get
Console.WriteLine(obj.EmployeeID);     //123456
Console.WriteLine(obj.EmployeeName);   //John
Console.WriteLine(obj.Designation);    //Tech Lead

编辑:下面是我的类Field的外观:

public class Field
{
    public Field(string name, Type type)
    {
        this.FieldName = name;
        this.FieldType = type;
    }

    public string FieldName;

    public Type FieldType;
}

您可以考虑使用动态模块和类来完成这项工作。唯一的缺点是它仍然加载在应用程序域中。但是。net 4.0支持可收集的动态程序集,因此你可以动态地重新创建类/类型。

这需要一些工作,但肯定不是不可能的。

我所做的是:

在字符串中创建c#源代码(不需要写入文件), 通过Microsoft.CSharp.CSharpCodeProvider (CompileAssemblyFromSource)运行它 查找生成的类型 并创建该类型的实例(Activator.CreateInstance)

这样您就可以处理已经知道的c#代码,而不必发出MSIL。

但是,如果你的类实现了一些接口(或从一些基类派生),这是最好的工作,否则调用代码(阅读:编译器)如何知道将在运行时生成的类?

根据@danijels的回答,在VB中动态创建一个类。NET:

Imports System.Reflection
Imports System.Reflection.Emit

Public Class ObjectBuilder

Public Property myType As Object
Public Property myObject As Object

Public Sub New(fields As List(Of Field))
    myType = CompileResultType(fields)
    myObject = Activator.CreateInstance(myType)
End Sub

Public Shared Function CompileResultType(fields As List(Of Field)) As Type
    Dim tb As TypeBuilder = GetTypeBuilder()
    Dim constructor As ConstructorBuilder = tb.DefineDefaultConstructor(MethodAttributes.[Public] Or MethodAttributes.SpecialName Or MethodAttributes.RTSpecialName)

    For Each field In fields
        CreateProperty(tb, field.Name, field.Type)
    Next

    Dim objectType As Type = tb.CreateType()
    Return objectType
End Function

Private Shared Function GetTypeBuilder() As TypeBuilder
    Dim typeSignature = "MyDynamicType"
    Dim an = New AssemblyName(typeSignature)
    Dim assemblyBuilder As AssemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(an, AssemblyBuilderAccess.Run)
    Dim moduleBuilder As ModuleBuilder = assemblyBuilder.DefineDynamicModule("MainModule")
    Dim tb As TypeBuilder = moduleBuilder.DefineType(typeSignature, TypeAttributes.[Public] Or TypeAttributes.[Class] Or TypeAttributes.AutoClass Or TypeAttributes.AnsiClass Or TypeAttributes.BeforeFieldInit Or TypeAttributes.AutoLayout, Nothing)
    Return tb
End Function

Private Shared Sub CreateProperty(tb As TypeBuilder, propertyName As String, propertyType As Type)
    Dim fieldBuilder As FieldBuilder = tb.DefineField("_" & propertyName, propertyType, FieldAttributes.[Private])

    Dim propertyBuilder As PropertyBuilder = tb.DefineProperty(propertyName, PropertyAttributes.HasDefault, propertyType, Nothing)
    Dim getPropMthdBldr As MethodBuilder = tb.DefineMethod("get_" & propertyName, MethodAttributes.[Public] Or MethodAttributes.SpecialName Or MethodAttributes.HideBySig, propertyType, Type.EmptyTypes)
    Dim getIl As ILGenerator = getPropMthdBldr.GetILGenerator()

    getIl.Emit(OpCodes.Ldarg_0)
    getIl.Emit(OpCodes.Ldfld, fieldBuilder)
    getIl.Emit(OpCodes.Ret)

    Dim setPropMthdBldr As MethodBuilder = tb.DefineMethod("set_" & propertyName, MethodAttributes.[Public] Or MethodAttributes.SpecialName Or MethodAttributes.HideBySig, Nothing, {propertyType})

    Dim setIl As ILGenerator = setPropMthdBldr.GetILGenerator()
    Dim modifyProperty As Label = setIl.DefineLabel()
    Dim exitSet As Label = setIl.DefineLabel()

    setIl.MarkLabel(modifyProperty)
    setIl.Emit(OpCodes.Ldarg_0)
    setIl.Emit(OpCodes.Ldarg_1)
    setIl.Emit(OpCodes.Stfld, fieldBuilder)

    setIl.Emit(OpCodes.Nop)
    setIl.MarkLabel(exitSet)
    setIl.Emit(OpCodes.Ret)

    propertyBuilder.SetGetMethod(getPropMthdBldr)
    propertyBuilder.SetSetMethod(setPropMthdBldr)
End Sub

End Class