How to create a new object instance from a Type

Question

One may not always know the Type of an object at compile-time  but may need to create an instance of the Type     How do you get a new object instance from a Type

User · Answer

Just as an extra to anyone using the above answers that implement:

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

Be careful - if your Constructor isn't "Public" then you will get the following error:

"System.MissingMethodException: 'No parameterless constructor defined for this object."

Your class can be Internal/Friend, or whatever you need but the constructor must be public.

User · Answer

Given this problem the Activator will work when there is a parameterless ctor  If this is a constraint consider using   System Runtime Serialization FormatterServices GetSafeUninitializedObject

User · Answer

Wouldn t the generic T t   new T    work

User · Answer

If this is for something that will be called a lot in an application instance  it s a lot faster to compile and cache dynamic code instead of using the activator or ConstructorInfo Invoke     Two easy options for dynamic compilation are compiled Linq Expressions or some simple IL opcodes and DynamicMethod   Either way  the difference is huge when you start getting into tight loops or multiple calls

User · Answer

If you want to use the default constructor then the solution using System Activator presented earlier is probably the most convenient  However  if the type lacks a default constructor or you have to use a non-default one  then an option is to use reflection or System ComponentModel TypeDescriptor  In case of reflection  it is enough to know just the type name  with its namespace    Example using reflection   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          Example using 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

User · Answer

I can across this question because I was looking to implement a simple CloneObject method for arbitrary class  with a default constructor   With generic method you can require that the type implements 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   With non-generic assume the type has a default constructor and catch an exception if it doesn t   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       amp  ex Message      End Try     Return result End Function

User · Answer

ObjectType instance    ObjectType Activator CreateInstance objectType     The Activator class has a generic variant that makes this a bit easier   ObjectType instance   Activator CreateInstance lt ObjectType gt

User · Answer

The Activator class within the root System namespace is pretty powerful   There are a lot of overloads for passing parameters to the constructor and such  Check out the documentation at       http   msdn microsoft com en-us library system activator createinstance aspx   or  new path      https   docs microsoft com en-us dotnet api system activator createinstance   Here are some simple examples   ObjectType instance    ObjectType Activator CreateInstance objectType    ObjectType instance    ObjectType Activator CreateInstance  MyAssembly   MyNamespace ObjectType

User · Answer

public AbstractType New       get               return  AbstractType  Activator CreateInstance GetType

User · Answer

Compiled expression is best way   for performance to repeatedly create instance in runtime    static readonly Func lt X gt  YCreator   Expression Lambda lt Func lt X gt  gt      Expression New typeof Y  GetConstructor Type EmptyTypes      Compile     X x   YCreator      Statistics  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   Statistics  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   Statistics  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   Statistics  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   Statistics  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   Statistics  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   Full code   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 lt X gt  YCreator   Expression Lambda lt Func lt X gt  gt      Expression New typeof Y  GetConstructor Type EmptyTypes     Compile    static X CreateY CompiledExpression         return YCreator       private static readonly Func lt X gt  YCreator Type   Expression Lambda lt Func lt X gt  gt      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 lt int  X gt  YCreator Arg   Expression Lambda lt Func lt int  X gt  gt      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 lt X gt  CreateY CreateInstance           new  Name    Activator CreateInstance Type type    Creator    Func lt X gt  CreateY CreateInstance           new  Name    ConstructorInfo Invoke   Creator    Func lt X gt  CreateY Invoke           new  Name    Compiled expression   Creator    Func lt X gt  CreateY CompiledExpression           new  Name    Compiled expression  type    Creator    Func lt X gt  CreateY CompiledExpression Type           new  Name    new   Creator    Func lt X gt  CreateY New                        var creator   creatorInfo Creator           var sum   0          for  var i   0  i  lt  1000  i                sum    creator   Z           var stopwatch   new Stopwatch            stopwatch Start            for  var i   0  i  lt  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 lt int  X gt  CreateY CreateInstance Arg           new  Name    ConstructorInfo Invoke   Creator    Func lt int  X gt  CreateY Invoke Arg           new  Name    Compiled expression   Creator    Func lt int  X gt  CreateY CompiledExpression Arg           new  Name    new   Creator    Func lt int  X gt  CreateY New Arg                        var creator   creatorInfo Creator           var sum   0          for  var i   0  i  lt  1000  i                sum    creator i  Z           var stopwatch   new Stopwatch            stopwatch Start            for  var i   0  i  lt  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

User · Answer

Its pretty simple  Assume that your classname is Car and the namespace is Vehicles  then pass the parameter as Vehicles Car which returns object of type Car  Like this you can create any instance of any class dynamically   public object GetInstance string strNamesapace                  Type t   Type GetType strNamesapace         return  Activator CreateInstance t                If your Fully Qualified Name ie  Vehicles Car in this case  is in another assembly  the Type GetType will be null  In such cases  you have loop through all assemblies and find the Type  For that you can use the below code  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       And you can get the instance by calling the above method   object objClassInstance   GetInstance  Vehicles Car

User · Answer

Without use of Reflection   private T Create lt T gt    where T   class  new         return new T

[c#] How to create a new object instance from a Type

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