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。
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;
}
对于那些想要创建一个动态类的属性(即POCO),并创建这个类的列表。使用后面提供的代码,这将创建一个动态类,并创建一个该类的列表。
var properties = new List<DynamicTypeProperty>()
{
new DynamicTypeProperty("doubleProperty", typeof(double)),
new DynamicTypeProperty("stringProperty", typeof(string))
};
// create the new type
var dynamicType = DynamicType.CreateDynamicType(properties);
// create a list of the new type
var dynamicList = DynamicType.CreateDynamicList(dynamicType);
// get an action that will add to the list
var addAction = DynamicType.GetAddAction(dynamicList);
// call the action, with an object[] containing parameters in exact order added
addAction.Invoke(new object[] {1.1, "item1"});
addAction.Invoke(new object[] {2.1, "item2"});
addAction.Invoke(new object[] {3.1, "item3"});
下面是前面代码使用的类。
注意:你还需要引用Microsoft.CodeAnalysis.CSharp库。
/// <summary>
/// A property name, and type used to generate a property in the dynamic class.
/// </summary>
public class DynamicTypeProperty
{
public DynamicTypeProperty(string name, Type type)
{
Name = name;
Type = type;
}
public string Name { get; set; }
public Type Type { get; set; }
}
public static class DynamicType
{
/// <summary>
/// Creates a list of the specified type
/// </summary>
/// <param name="type"></param>
/// <returns></returns>
public static IEnumerable<object> CreateDynamicList(Type type)
{
var listType = typeof(List<>);
var dynamicListType = listType.MakeGenericType(type);
return (IEnumerable<object>) Activator.CreateInstance(dynamicListType);
}
/// <summary>
/// creates an action which can be used to add items to the list
/// </summary>
/// <param name="listType"></param>
/// <returns></returns>
public static Action<object[]> GetAddAction(IEnumerable<object> list)
{
var listType = list.GetType();
var addMethod = listType.GetMethod("Add");
var itemType = listType.GenericTypeArguments[0];
var itemProperties = itemType.GetProperties();
var action = new Action<object[]>((values) =>
{
var item = Activator.CreateInstance(itemType);
for(var i = 0; i < values.Length; i++)
{
itemProperties[i].SetValue(item, values[i]);
}
addMethod.Invoke(list, new []{item});
});
return action;
}
/// <summary>
/// Creates a type based on the property/type values specified in the properties
/// </summary>
/// <param name="properties"></param>
/// <returns></returns>
/// <exception cref="Exception"></exception>
public static Type CreateDynamicType(IEnumerable<DynamicTypeProperty> properties)
{
StringBuilder classCode = new StringBuilder();
// Generate the class code
classCode.AppendLine("using System;");
classCode.AppendLine("namespace Dexih {");
classCode.AppendLine("public class DynamicClass {");
foreach (var property in properties)
{
classCode.AppendLine($"public {property.Type.Name} {property.Name} {{get; set; }}");
}
classCode.AppendLine("}");
classCode.AppendLine("}");
var syntaxTree = CSharpSyntaxTree.ParseText(classCode.ToString());
var references = new MetadataReference[]
{
MetadataReference.CreateFromFile(typeof(object).GetTypeInfo().Assembly.Location),
MetadataReference.CreateFromFile(typeof(DictionaryBase).GetTypeInfo().Assembly.Location)
};
var compilation = CSharpCompilation.Create("DynamicClass" + Guid.NewGuid() + ".dll",
syntaxTrees: new[] {syntaxTree},
references: references,
options: new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
using (var ms = new MemoryStream())
{
var result = compilation.Emit(ms);
if (!result.Success)
{
var failures = result.Diagnostics.Where(diagnostic =>
diagnostic.IsWarningAsError ||
diagnostic.Severity == DiagnosticSeverity.Error);
var message = new StringBuilder();
foreach (var diagnostic in failures)
{
message.AppendFormat("{0}: {1}", diagnostic.Id, diagnostic.GetMessage());
}
throw new Exception($"Invalid property definition: {message}.");
}
else
{
ms.Seek(0, SeekOrigin.Begin);
var assembly = System.Runtime.Loader.AssemblyLoadContext.Default.LoadFromStream(ms);
var dynamicType = assembly.GetType("Dexih.DynamicClass");
return dynamicType;
}
}
}
}
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);
}
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