C# 如何从类型创建新的对象实例_C#_.net_Performance_Reflection_Types

C# 如何从类型创建新的对象实例

c# .net performance reflection types

C# 如何从类型创建新的对象实例,c#,.net,performance,reflection,types,C#,.net,Performance,Reflection,Types,编译时可能并不总是知道对象的类型，但可能需要创建类型的实例如何从类型获取新的对象实例？根系统命名空间中的激活器类功能非常强大有很多重载用于将参数传递给构造函数等。请访问以下网址查看文档：或（新路径）以下是一些简单的例子： ObjectType instance = (ObjectType)Activator.CreateInstance(objectType); ObjectType instance = (ObjectType)Activator.CreateInstance("

编译时可能并不总是知道对象的

类型

，但可能需要创建

类型

的实例

如何从

类型

获取新的对象实例？

根

系统

命名空间中的

激活器

类功能非常强大

有很多重载用于将参数传递给构造函数等。请访问以下网址查看文档：

或（新路径）

以下是一些简单的例子：

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

ObjectType instance = (ObjectType)Activator.CreateInstance("MyAssembly","MyNamespace.ObjectType");

如果这是为了在应用程序实例中大量调用的东西，那么编译和缓存动态代码比使用activator或

ConstructorInfo.Invoke（）

要快得多。动态编译的两个简单选项是编译的或一些简单的。无论哪种方式，当您开始进入紧密循环或多次调用时，差异都是巨大的

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

Activator

类有一个通用的变体，使它更容易实现：

ObjectType instance = Activator.CreateInstance<ObjectType>();

ObjectType instance=Activator.CreateInstance（）；

通用的

t t=newt（）工作
 如果要使用默认构造函数，那么前面介绍的使用System.Activator
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必须使用非默认构造函数，则可以选择使用反射或System.ComponentModel.TypeDescriptor
。在反射的情况下，只知道类型名（及其名称空间）就足够了
public AbstractType New
{
    get
    {
        return (AbstractType) Activator.CreateInstance(GetType());
    }
}

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
    );

private T Create<T>() where T : class, new()
{
    return new T();
}

使用类型描述符的示例：
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 }
    );

这很简单。假设您的类名是Car
，名称空间是Vehicles
，然后将参数作为Vehicles.Car
传递，它返回类型为Car
的对象。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（即本例中的Vehicles.Car
）位于另一个部件中，Type.GetType
将为空。在这种情况下，您需要遍历所有程序集并找到类型
。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;
 }

您可以通过调用上述方法来获取实例
object objClassInstance = GetInstance("Vehicles.Car");

我可以跨越这个问题，因为我想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，可以要求类型实现New（）
对于非泛型，假设该类型具有默认构造函数和catch
如果没有，则为异常
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

编译表达式是最好的方式！（为了提高性能，可以在运行时重复创建实例）
统计数据（2015年，.net 4.5x64）：
统计数据（2015年，.net 4.5，x86）：
统计数据（2017年，LINQPad 5.22.02/x64/.NET 4.6）：
统计数据（2019年，x64/.NET 4.8）：
统计数据（2019年，x64/.NET Core 3.0）：
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) {}
}

static X CreateY_New（）
{
返回新的Y（）；
}
静态X创建新参数（整数z）
{
返回新的Y（z）；
}
静态X CreateY_CreateInstance（）
{
返回（X）Activator.CreateInstance（typeof（Y））；
}
静态X CreateY_CreateInstance_String（）
{
返回（X）Activator.CreateInstance（“程序”，“Y”）.Unwrap（）；
}
静态X CreateY_CreateInstance_Arg（int z）
{
返回（X）Activator.CreateInstance（typeof（Y），新对象[]{z，}）；
}
私有静态只读System.Reflection.ConstructorInfo YConstructor=
typeof（Y）.GetConstructor（Type.EmptyTypes）；
私有静态只读对象[]空=新对象[]{}；
静态X CreateY_Invoke（）
{
return（X）YConstructor.Invoke（空）；
}
私有静态只读System.Reflection.ConstructorInfo YConstructor_Arg=
typeof（Y）.GetConstructor（新[]{typeof（int），}）；
静态X CreateY_Invoke_Arg（intz）
{
返回（X）YConstructor_Arg.Invoke（新对象[]{z，}）；
}
私有静态只读Func YCreator=Expression.Lambda(
Expression.New（typeof（Y）.GetConstructor（Type.EmptyTypes））
).Compile（）；
静态X CreateY_CompiledExpression（）
{
返回YCreator（）；
}
私有静态只读Func YCreator_Type=Expression.Lambda(
新表达式（Y型）
).Compile（）；
静态X CreateY_编译表达式_Type（）
{
返回YCreator_Type（）；
}
私有静态只读参数Expression YCreator_Arg_Param=Expression.Parameter（typeof（int），“z”）；
私有静态只读Func YCreator_Arg=Expression.Lambda(
Expression.New（typeof（Y）.GetConstructor（New[]{typeof（int），}），New[]{YCreator_Arg_Param，}），
YCreator_Arg_Param
).Compile（）；
静态X CreateY_编译表达式_Arg（int z）
{
返回YCreator_Arg（z）；
}
静态void Main（字符串[]参数）
{
const int迭代次数=5000000；
WriteLine（“迭代：{0}”，迭代）；
Console.WriteLine（“无参数”）；
foreach（新版本中的var creatorInfo[]
{
新建{Name=“Activator.CreateInstance（string assemblyName，string typeName）”，Creator=（Func）CreateY_CreateInstance}，
新建{Name=“Activator.CreateInstance（Type类型）”，Creator=（Func）CreateY_CreateInstance}，
新建{Name=“ConstructorInfo.Invoke”，Creator=（Func）CreateY_Invoke}，
新的{Name=“Compiled expression”，Creator=（Func）CreateY_Compiled expression}，
新建{Name=“Compiled expression（type）”，Creator=（Func）CreateY\u Compiled expression\u type}，
新建{Name=“new”，Creator=（Func）CreateY_new}，
})
{
var creator=creatorInfo.creator；
var总和=0；
对于（变量i=0；i<1000；i++）
sum+=creator（）.Z；
var stopwatch=新秒表（）；
秒表。开始（）；
对于（变量i=0；i    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

    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

    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

    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

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

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

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) {}
}

private T Create<T>() where T : class, new()
{
    return new T();
}

System.Runtime.Serialization.FormatterServices.GetSafeUninitializedObject()

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