Type.GetConstructor Method (BindingFlags, Binder, array<Type[], array<ParameterModifier[])

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Searches for a constructor whose parameters match the specified argument types and modifiers, using the specified binding constraints.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

Syntax

'Declaration
<ComVisibleAttribute(True)> _
Public Function GetConstructor ( _
    bindingAttr As BindingFlags, _
    binder As Binder, _
    types As Type(), _
    modifiers As ParameterModifier() _
) As ConstructorInfo

[ComVisibleAttribute(true)]
public ConstructorInfo GetConstructor(
    BindingFlags bindingAttr,
    Binder binder,
    Type[] types,
    ParameterModifier[] modifiers
)

Parameters

• bindingAttr
  Type: System.Reflection.BindingFlags
  A bitmask comprised of one or more BindingFlags that specify how the search is conducted.
  -or-
  Zero, to return nulla null reference (Nothing in Visual Basic).

• binder
  Type: System.Reflection.Binder
  A Binder object that defines a set of properties and enables binding, which can involve selection of an overloaded method, coercion of argument types, and invocation of a member through reflection.
  -or-
  A null reference (Nothing in Visual Basic), to use the DefaultBinder.

• types
  Type: array<System.Type[]
  An array of Type objects representing the number, order, and type of the parameters for the constructor to get.
  -or-
  An empty array of the type Type (that is, Type[] types = new Type[0]) to get a constructor that takes no parameters.
  -or-
  EmptyTypes .

• modifiers
  Type: array<System.Reflection.ParameterModifier[]
  An array of ParameterModifier objects representing the attributes associated with the corresponding element in the parameter type array. The default binder does not process this parameter.

Return Value

Type: System.Reflection.ConstructorInfo
A ConstructorInfo object representing the constructor that matches the specified requirements, if found; otherwise, nulla null reference (Nothing in Visual Basic).

Exceptions

Exception	Condition
ArgumentNullException	types is nulla null reference (Nothing in Visual Basic). -or- One of the elements in types is nulla null reference (Nothing in Visual Basic).
ArgumentException	types is multidimensional. -or- modifiers is multidimensional. -or- types and modifiers do not have the same length.

Remarks

The types array and the modifiers array have the same length. A parameter specified in the types array can have the following attributes, which are specified in the modifiers array: pdIn, pdOut, pdLcid, pdRetval, pdOptional, and pdHasDefault, which represent [In], [Out], [lcid], [retval], [optional], and a value specifying whether the parameter has a default value. A parameter's associated attributes are stored in the metadata and enhance interoperability.

If an exact match does not exist, the binder will attempt to coerce the parameter types specified in the types array in order to select a match. If the binder is unable to select a match, then nulla null reference (Nothing in Visual Basic) is returned.

The following BindingFlags filter flags can be used to define which constructors to include in the search:

• You must specify either BindingFlags.Instance or BindingFlags.Static in order to get a return.

• Specify BindingFlags.Public to include public constructors in the search.

• Specify BindingFlags.NonPublic to include non-public constructors (that is, private and protected constructors) in the search.

See System.Reflection.BindingFlags for more information.

To get the class initializer (.cctor) using this method overload, you must specify BindingFlags.Static | BindingFlags.NonPublic (BindingFlags.StaticOrBindingFlags.NonPublic in Visual Basic).

Note:
You cannot omit parameters when looking up constructors and methods. You can only omit parameters when invoking.

If the current Type represents a constructed generic type, this method returns the ConstructorInfo with the type parameters replaced by the appropriate type arguments. If the current Type represents a type parameter in the definition of a generic type or generic method, this method always returns nulla null reference (Nothing in Visual Basic).

Platform Notes

 Silverlight for Windows Phone

 GetConstructor throws an ArgumentNullException exception when modifiers is nulla null reference (Nothing in Visual Basic). On Windows, no exception is thrown.

Examples

The following program obtains the type of MyClass1 class, gets the ConstructorInfo object matching the specified binding flags, and displays the signature of the constructor.

Note:
To run this example, see Building Examples That Use a Demo Method and a TextBlock Control.

Public Class Example
    Public Sub New(ByVal i As Integer)
    End Sub

    Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

         Dim myType As Type = GetType(Example)
         Dim parameters() As Type = { GetType(Int32) }

         ' Get the public instance constructor that takes an integer parameter.
         Dim ctor As ConstructorInfo = myType.GetConstructor( _
             BindingFlags.Instance Or BindingFlags.Public, _
             Type.DefaultBinder, _
             parameters, _
             Nothing)

         If ctor Is Nothing Then
             outputBlock.Text &= _
                 "There is no public instance constructor of MyClass " & _
                 "that takes an integer as a parameter." & vbCrLf
         Else
             outputBlock.Text &= _
                 "The public constructor of MyClass that takes an integer " & _
                 "as a parameter is: " & vbCrLf
             outputBlock.Text &= ctor.ToString() & vbCrLf
         End If

    End Sub 
End Class 

' This example produces the following output:
'
'The public constructor of MyClass that takes an integer as a parameter is:
'Void .ctor(Int32)

using System;
using System.Reflection;
using System.Security;

public class Example
{
    public Example(int i) { }

    public static void Demo(System.Windows.Controls.TextBlock outputBlock)
    {
        Type myType = typeof(Example);
        Type[] parameters = { typeof(int) };

        // Get the constructor that takes an integer as a parameter.
        ConstructorInfo ctor = myType.GetConstructor(
            BindingFlags.Instance | BindingFlags.Public, 
            Type.DefaultBinder,
            parameters,
            null);

        if (ctor == null)
        {
            outputBlock.Text += 
                "There is no public constructor of MyClass that takes an integer as a parameter.\n";
        }
        else
        {
            outputBlock.Text += 
                "The public constructor of MyClass that takes an integer as a parameter is:\n"; 
            outputBlock.Text += ctor.ToString() + "\n";
        }
    }
}

/* This example produces the following output:

The public constructor of MyClass that takes an integer as a parameter is:
Void .ctor(Int32)
 */

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

See Also

Reference

Type Class

GetConstructor Overload

System Namespace

ConstructorInfo

BindingFlags

Binder

DefaultBinder

ParameterModifier

GetConstructorImpl

GetConstructors