PRB: "System.InvalidOperationException" Error While Serializing a Class Without Default Constructor (816225)

Beta Information

This article discusses a Beta release of a Microsoft product. The information in this article is provided as-is and is subject to change without notice.

No formal product support is available from Microsoft for this Beta product. For information about how to obtain support for a Beta release, see the documentation that is included with the Beta product files, or check the Web location from which you downloaded the release.

SYMPTOMS

When you create an XmlSerializer object to serialize a class without a default constructor, you may receive the following error message:

An unhandled exception of type 'System.InvalidOperationException' occurred in system.xml.dll

Additional information: ApplicationName.ClassName cannot be serialized because it does not have a default public constructor.

CAUSE

To be serialized by an XmlSerializer object, a class must have a default constructor. For additional information about XML Serialization Considerations, visit the following Microsoft Web site:

http://msdn.microsoft.com/library/en-us/cpguide/html/cpconintroducingxmlserialization.asp

WORKAROUND

To work around this problem, add the default constructor without parameter to the class so that the XMLSerializer can serialize the object without error. The following code demonstrates how to add the default constructor to the class that is used in the sample code of the "More Information" section:

Visual C# .NET Code

   public class TestClass 
   {
      private string UserName;

      // Add the Default Constructor
      public TestClass()
      {
         // Default Constructor without parameter
      }

      // Existing Constructor
      public TestClass(string name)  
      {
         UserName = name;
      }
   }

Visual Basic .NET Code

   Public Class TestClass
      Public UserName As String

      ' Add the Default Constructor
      Public Sub New()
         ' Default Constructor without parameter
      End Sub
      
      ' Existing Constructor
      Public Sub New(ByVal name As String)
         UserName = name
      End Sub
   End Class

MORE INFORMATION

Steps to Reproduce the Behavior

Start Microsoft Visual Studio .NET.
On the File menu, point to New, and then click Project.
Under Project Types, click Visual C# .NET or Visual Basic .NET, and then click Console Application under Templates.
Name the project ConstructorTestingApplication, and then click OK.

Replace the existing code with the following code:

Visual C# .NET Code

using System;
using System.Xml;
using System.Xml.Schema;
using System.Xml.Serialization;

namespace ConstructorTestingApplication
{
	public class TestClass 
	{
		public string UserName;

		// Constructor, No default constructor
		public TestClass(string name)  
		{
			UserName = name;
		}
	}
	
	// Class having Main Method
	public class MainClass
	{
    
		public static void Main() 
		{
			// initializing XmlSerializer object with typeof TestClass
			XmlSerializer ser = new XmlSerializer(typeof(TestClass));
		}
	}
}

Visual Basic .NET Code

Imports System
Imports System.Xml
Imports System.Xml.Schema
Imports System.Xml.Serialization

Public Class TestClass
    Public UserName As String

    ' Constructor, No default constructor
    Public Sub New(ByVal name As String)
        UserName = name
    End Sub
End Class
Module Module1

    Sub Main()
        ' initializing XmlSerializer object with typeof TestClass
        Dim ser As New XmlSerializer(GetType(TestClass))
    End Sub

End Module

On the Debug menu, click Start. You receive the error message that is described in the "Symptoms" section.

PRB: "System.InvalidOperationException" Error While Serializing a Class Without Default Constructor (816225)

Beta Information

SYMPTOMS

CAUSE

WORKAROUND

Visual C# .NET Code

Visual Basic .NET Code

STATUS

MORE INFORMATION

Steps to Reproduce the Behavior

Visual C# .NET Code

Visual Basic .NET Code

REFERENCES