如何从Type创建新的对象实例

c# .net performance reflection types

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12回复

30252 作者的声誉

人们可能并不总是Type在编译时知道对象,但可能需要创建一个实例Type。你如何从一个新的对象实例Type

作者: tags2k 的来源 发布者: 2008 年 8 月 3 日

回应 12


42

30252 作者的声誉

此问题的一个实现是尝试调用Type的无参数构造函数:

public static object GetNewObject(Type t)
{
    try
    {
        return t.GetConstructor(new Type[] { }).Invoke(new object[] { });
    }
    catch
    {
        return null;
    }
}

这是一种通用方法中包含的相同方法:

public static T GetNewObject<T>()
{
    try
    {
        return (T)typeof(T).GetConstructor(new Type[] { }).Invoke(new object[] { });
    }
    catch
    {
        return default(T);
    }
}
作者: tags2k 发布者: 2008 年 8 月 3 日

817

17852 作者的声誉

决定

ActivatorSystem命名空间中的类非常强大。

将参数传递给构造函数等有很多重载。查看以下文档:

http://msdn.microsoft.com/en-us/library/system.activator.createinstance.aspx

或(新路径)

https://docs.microsoft.com/en-us/dotnet/api/system.activator.createinstance

以下是一些简单的例子:

ObjectType instance = (ObjectType)Activator.CreateInstance(objectType);

ObjectType instance = (ObjectType)Activator.CreateInstance("MyAssembly","MyNamespace.ObjectType");
作者: Karl Seguin 发布者: 2008 年 8 月 3 日

12

5841 作者的声誉

如果这是在应用程序实例中被大量调用的东西,那么编译和缓存动态代码而不是使用激活器或更快的速度要快得多ConstructorInfo.Invoke()。动态编译的两个简单选项是编译Linq表达式或一些简单的IL操作码和DynamicMethod。无论哪种方式,当您开始进入紧密循环或多个呼叫时,差异是巨大的。

作者: Tom Mayfield 发布者: 2008 年 8 月 25 日

130

413307 作者的声誉

ObjectType instance = (ObjectType)Activator.CreateInstance(objectType);

Activator班有一个通用的变种,使这是一个更容易一些:

ObjectType instance = Activator.CreateInstance<ObjectType>();
作者: Konrad Rudolph 发布者: 2008 年 8 月 25 日

9

4669 作者的声誉

通用T t = new T();工作不会吗?

作者: Brady Moritz 发布者: 2010 年 8 月 17 日

3

416 作者的声誉

public AbstractType New
{
    get
    {
        return (AbstractType) Activator.CreateInstance(GetType());
    }
}
作者: vikram nayak 发布者: 2012 年 9 月 9 日

8

481 作者的声誉

如果您想使用默认构造函数,那么System.Activator前面介绍的解决方案可能是最方便的。但是,如果类型缺少默认构造函数或者您必须使用非默认构造函数,则选项是使用反射或System.ComponentModel.TypeDescriptor。在反射的情况下,只知道类型名称(及其名称空间)就足够了。

使用反射的示例:

ObjectType instance = 
    (ObjectType)System.Reflection.Assembly.GetExecutingAssembly().CreateInstance(
        typeName: objectType.FulName, // string including namespace of the type
        ignoreCase: false,
        bindingAttr: BindingFlags.Default,
        binder: null,  // use default binder
        args: new object[] { args, to, constructor },
        culture: null, // use CultureInfo from current thread
        activationAttributes: null
    );

示例使用TypeDescriptor

ObjectType instance = 
    (ObjectType)System.ComponentModel.TypeDescriptor.CreateInstance(
        provider: null, // use standard type description provider, which uses reflection
        objectType: objectType,
        argTypes: new Type[] { types, of, args },
        args: new object[] { args, to, constructor }
    );
作者: BSharp 发布者: 2013 年 7 月 22 日

14

11842 作者的声誉

它非常简单。假设您的类名是Car和命名空间Vehicles,然后传递Vehicles.Car返回类型对象的参数Car。像这样,您可以动态创建任何类的任何实例。

public object GetInstance(string strNamesapace)
{         
     Type t = Type.GetType(strNamesapace); 
     return  Activator.CreateInstance(t);         
}

如果您的完全限定名称(即,Vehicles.Car在这种情况下)在另一个程序集中,Type.GetType则将为null。在这种情况下,你循环遍历所有程序集并找到Type。为此,您可以使用以下代码

public object GetInstance(string strFullyQualifiedName)
{
     Type type = Type.GetType(strFullyQualifiedName);
     if (type != null)
         return Activator.CreateInstance(type);
     foreach (var asm in AppDomain.CurrentDomain.GetAssemblies())
     {
         type = asm.GetType(strFullyQualifiedName);
         if (type != null)
             return Activator.CreateInstance(type);
     }
     return null;
 }

您可以通过调用上面的方法来获取实例。

object objClassInstance = GetInstance("Vehicles.Car");
作者: Sarath Avanavu 发布者: 2014 年 11 月 3 日

3

1535 作者的声誉

我可以跨越这个问题,因为我正在寻找为任意类实现一个简单的CloneObject方法(使用默认构造函数)

使用泛型方法,您可以要求类型实现New()。

Public Function CloneObject(Of T As New)(ByVal src As T) As T
    Dim result As T = Nothing
    Dim cloneable = TryCast(src, ICloneable)
    If cloneable IsNot Nothing Then
        result = cloneable.Clone()
    Else
        result = New T
        CopySimpleProperties(src, result, Nothing, "clone")
    End If
    Return result
End Function

对于非泛型假设,类型具有默认构造函数,如果不是,则捕获异常。

Public Function CloneObject(ByVal src As Object) As Object
    Dim result As Object = Nothing
    Dim cloneable As ICloneable
    Try
        cloneable = TryCast(src, ICloneable)
        If cloneable IsNot Nothing Then
            result = cloneable.Clone()
        Else
            result = Activator.CreateInstance(src.GetType())
            CopySimpleProperties(src, result, Nothing, "clone")
        End If
    Catch ex As Exception
        Trace.WriteLine("!!! CloneObject(): " & ex.Message)
    End Try
    Return result
End Function
作者: Darrel Lee 发布者: 2015 年 3 月 24 日

108

11502 作者的声誉

编译表达式是最好的方法!(用于在运行时重复创建实例的性能)。

static readonly Func<X> YCreator = Expression.Lambda<Func<X>>(
   Expression.New(typeof(Y).GetConstructor(Type.EmptyTypes))
 ).Compile();

X x = YCreator();

统计(2012年):

    Iterations: 5000000
    00:00:00.8481762, Activator.CreateInstance(string, string)
    00:00:00.8416930, Activator.CreateInstance(type)
    00:00:06.6236752, ConstructorInfo.Invoke
    00:00:00.1776255, Compiled expression
    00:00:00.0462197, new

统计(2015年,.net 4.5,x64):

    Iterations: 5000000
    00:00:00.2659981, Activator.CreateInstance(string, string)
    00:00:00.2603770, Activator.CreateInstance(type)
    00:00:00.7478936, ConstructorInfo.Invoke
    00:00:00.0700757, Compiled expression
    00:00:00.0286710, new

统计(2015年,.net 4.5,x86):

    Iterations: 5000000
    00:00:00.3541501, Activator.CreateInstance(string, string)
    00:00:00.3686861, Activator.CreateInstance(type)
    00:00:00.9492354, ConstructorInfo.Invoke
    00:00:00.0719072, Compiled expression
    00:00:00.0229387, new

统计(2017年,LINQPad 5.22.02 / x64 / .NET 4.6):

    Iterations: 5000000
    No args
    00:00:00.3897563, Activator.CreateInstance(string assemblyName, string typeName)
    00:00:00.3500748, Activator.CreateInstance(Type type)
    00:00:01.0100714, ConstructorInfo.Invoke
    00:00:00.1375767, Compiled expression
    00:00:00.1337920, Compiled expression (type)
    00:00:00.0593664, new
    Single arg
    00:00:03.9300630, Activator.CreateInstance(Type type)
    00:00:01.3881770, ConstructorInfo.Invoke
    00:00:00.1425534, Compiled expression
    00:00:00.0717409, new

统计(2019,x64 / .NET 4.8):

Iterations: 5000000
No args
00:00:00.3287835, Activator.CreateInstance(string assemblyName, string typeName)
00:00:00.3122015, Activator.CreateInstance(Type type)
00:00:00.8035712, ConstructorInfo.Invoke
00:00:00.0692854, Compiled expression
00:00:00.0662223, Compiled expression (type)
00:00:00.0337862, new
Single arg
00:00:03.8081959, Activator.CreateInstance(Type type)
00:00:01.2507642, ConstructorInfo.Invoke
00:00:00.0671756, Compiled expression
00:00:00.0301489, new

统计(2019,x64 / .NET Core 3.0):

Iterations: 5000000
No args
00:00:00.3226895, Activator.CreateInstance(string assemblyName, string typeName)
00:00:00.2786803, Activator.CreateInstance(Type type)
00:00:00.6183554, ConstructorInfo.Invoke
00:00:00.0483217, Compiled expression
00:00:00.0485119, Compiled expression (type)
00:00:00.0434534, new
Single arg
00:00:03.4389401, Activator.CreateInstance(Type type)
00:00:01.0803609, ConstructorInfo.Invoke
00:00:00.0554756, Compiled expression
00:00:00.0462232, new

完整代码:

static X CreateY_New()
{
    return new Y();
}

static X CreateY_New_Arg(int z)
{
    return new Y(z);
}

static X CreateY_CreateInstance()
{
    return (X)Activator.CreateInstance(typeof(Y));
}

static X CreateY_CreateInstance_String()
{
    return (X)Activator.CreateInstance("Program", "Y").Unwrap();
}

static X CreateY_CreateInstance_Arg(int z)
{
    return (X)Activator.CreateInstance(typeof(Y), new object[] { z, });
}

private static readonly System.Reflection.ConstructorInfo YConstructor =
    typeof(Y).GetConstructor(Type.EmptyTypes);
private static readonly object[] Empty = new object[] { };
static X CreateY_Invoke()
{
    return (X)YConstructor.Invoke(Empty);
}

private static readonly System.Reflection.ConstructorInfo YConstructor_Arg =
    typeof(Y).GetConstructor(new[] { typeof(int), });
static X CreateY_Invoke_Arg(int z)
{
    return (X)YConstructor_Arg.Invoke(new object[] { z, });
}

private static readonly Func<X> YCreator = Expression.Lambda<Func<X>>(
   Expression.New(typeof(Y).GetConstructor(Type.EmptyTypes))
).Compile();
static X CreateY_CompiledExpression()
{
    return YCreator();
}

private static readonly Func<X> YCreator_Type = Expression.Lambda<Func<X>>(
   Expression.New(typeof(Y))
).Compile();
static X CreateY_CompiledExpression_Type()
{
    return YCreator_Type();
}

private static readonly ParameterExpression YCreator_Arg_Param = Expression.Parameter(typeof(int), "z");
private static readonly Func<int, X> YCreator_Arg = Expression.Lambda<Func<int, X>>(
   Expression.New(typeof(Y).GetConstructor(new[] { typeof(int), }), new[] { YCreator_Arg_Param, }),
   YCreator_Arg_Param
).Compile();
static X CreateY_CompiledExpression_Arg(int z)
{
    return YCreator_Arg(z);
}

static void Main(string[] args)
{
    const int iterations = 5000000;

    Console.WriteLine("Iterations: {0}", iterations);

    Console.WriteLine("No args");
    foreach (var creatorInfo in new[]
    {
        new {Name = "Activator.CreateInstance(string assemblyName, string typeName)", Creator = (Func<X>)CreateY_CreateInstance},
        new {Name = "Activator.CreateInstance(Type type)", Creator = (Func<X>)CreateY_CreateInstance},
        new {Name = "ConstructorInfo.Invoke", Creator = (Func<X>)CreateY_Invoke},
        new {Name = "Compiled expression", Creator = (Func<X>)CreateY_CompiledExpression},
        new {Name = "Compiled expression (type)", Creator = (Func<X>)CreateY_CompiledExpression_Type},
        new {Name = "new", Creator = (Func<X>)CreateY_New},
    })
    {
        var creator = creatorInfo.Creator;

        var sum = 0;
        for (var i = 0; i < 1000; i++)
            sum += creator().Z;

        var stopwatch = new Stopwatch();
        stopwatch.Start();
        for (var i = 0; i < iterations; ++i)
        {
            var x = creator();
            sum += x.Z;
        }
        stopwatch.Stop();
        Console.WriteLine("{0}, {1}", stopwatch.Elapsed, creatorInfo.Name);
    }

    Console.WriteLine("Single arg");
    foreach (var creatorInfo in new[]
    {
        new {Name = "Activator.CreateInstance(Type type)", Creator = (Func<int, X>)CreateY_CreateInstance_Arg},
        new {Name = "ConstructorInfo.Invoke", Creator = (Func<int, X>)CreateY_Invoke_Arg},
        new {Name = "Compiled expression", Creator = (Func<int, X>)CreateY_CompiledExpression_Arg},
        new {Name = "new", Creator = (Func<int, X>)CreateY_New_Arg},
    })
    {
        var creator = creatorInfo.Creator;

        var sum = 0;
        for (var i = 0; i < 1000; i++)
            sum += creator(i).Z;

        var stopwatch = new Stopwatch();
        stopwatch.Start();
        for (var i = 0; i < iterations; ++i)
        {
            var x = creator(i);
            sum += x.Z;
        }
        stopwatch.Stop();
        Console.WriteLine("{0}, {1}", stopwatch.Elapsed, creatorInfo.Name);
    }
}

public class X
{
  public X() { }
  public X(int z) { this.Z = z; }
  public int Z;
}

public class Y : X
{
    public Y() {}
    public Y(int z) : base(z) {}
}
作者: Serj-Tm 发布者: 2015 年 4 月 30 日

9

0 作者的声誉

不使用反射:

private T Create<T>() where T : class, new()
{
    return new T();
}
作者: user887983 发布者: 2015 年 6 月 30 日

5

1967 作者的声誉

鉴于此问题,当存在无参数的ctor时,Activator将工作。如果这是一个约束考虑使用

System.Runtime.Serialization.FormatterServices.GetSafeUninitializedObject()
作者: Thulani Chivandikwa 发布者: 2015 年 6 月 30 日
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