Cómo crear una nueva instancia de objeto a partir de un Tipo

c# .net performance reflection types


Es posible que no siempre se sepa el Type de un objeto en tiempo de compilación, pero es posible que deba crear una instancia del Type .

¿Cómo se obtiene una nueva instancia de objeto de un Type ?




Answer 1 Karl Seguin


La clase Activator dentro del espacio de nombres del System raíz es bastante poderosa.

Hay muchas sobrecargas para pasar parámetros al constructor y cosas así.Revise la documentación en:

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

o (nuevo camino)

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

Aquí hay algunos ejemplos simples:

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

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



Answer 2 Konrad Rudolph


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

La clase Activator tiene una variante genérica que lo hace un poco más fácil:

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



Answer 3 Serj-Tm


¡La expresión recopilada es la mejor manera! (para que la actuación cree repetidamente la instancia en tiempo de ejecución).

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

X x = YCreator();

Estadísticas (2012):

    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

Estadísticas (2015,.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

Estadísticas (2015,.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

Estadísticas (2017,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

Estadísticas (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

Estadísticas (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

Código completo:

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) {}
}



Answer 4 tags2k


One implementation of this problem is to attempt to call the parameter-less constructor of the Type:

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

Here is the same approach, contained in a generic method:

public static T GetNewObject<T>()
{
    try
    {
        return (T)typeof(T).GetConstructor(new Type[] { }).Invoke(new object[] { });
    }
    catch
    {
        return default(T);
    }
}



Answer 5 Sarath Avanavu


Es bastante simple. Suponga que su nombre de clase es Car y el espacio de nombres es Vehicles , luego pase el parámetro como Vehicles.Car que devuelve el objeto de tipo Car . De esta manera, puede crear cualquier instancia de cualquier clase de forma dinámica.

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

Si su nombre completo (es decir, Vehicles.Car en este caso) está en otro ensamblaje, Type.GetType será nulo. En tales casos, debe recorrer todos los ensamblajes y encontrar el Type . Para eso puedes usar el siguiente código

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;
 }

Y puedes obtener la instancia llamando al método anterior.

object objClassInstance = GetInstance("Vehicles.Car");