BUG: Unhandled exception error occurs when you enumerate through the Hashtable (815634)

MORE INFORMATION

Steps to Reproduce the Problem

1. Run Visual Studio .NET. Create a new Class Library project.
   
   You can use either Visual Basic .NET or Visual C# .NET. Name the project InterfaceDLL.
2. Replace the existing code in the class with the following code:
   
   Visual Basic .NET Code

   Option Strict On
   Imports System
   Imports System.Collections
   Imports System.Runtime.Serialization
   Imports System.Collections.Specialized
   
   Namespace test.SystemSettingInterface
   
      Public Interface ISystemSetting
         ' Add elements to the Hashtable
         Sub Add(ByVal Key As Object, ByVal Value As Object)
   
         ' Function Returning IEnumerator for Hashtable
         ' This function throws error
         Function GetEnumerator() As IEnumerator
   
         ' Function Returning Hashtable directly
         ' This function can be used as a workaround for function GetEnumerator
         Function GetHashTable() As Hashtable
   
         ' Default Property for Enumeration
         Default Property Item(ByVal key As Object) As Object
         ' Count Returns the number of elements in the Hashtable
         ReadOnly Property Count() As Integer
         ' Test function
         Sub Test()
   
      End Interface
   End Namespace
   

   
   Visual C# .NET Code

   using System;
   using System.Collections;
   using System.Runtime.Serialization;
   using System.Collections.Specialized;
   
   namespace test.SystemSettingInterface
   {
   	public interface ISystemSetting
   	{
         // Add elements to the Hashtable
   		void Add( object Key, object Value );
   
         // Function Returning IEnumerator for Hashtable
         // This function throws error
         IEnumerator GetEnumerator();
         
         // Function Returning Hashtable directly
         // This function can be used as workaround for function GetEnumerator
   	   Hashtable GetHashtable();
   
         // Default Property for Enumeration
   		object this[object key]
   		{
            get;
   			set;
   		}
   
         // Count Returns the number of elements in the Hashtable
   		int Count
   		{
   			get;
   		}
   
         // Test function
         void Test();
   	}  
   }
   

3. On the Build menu, click Build Solution to create InterfaceDLL.dll.
4. On the File menu, point to Add Project and then click New Project.
5. Add a new Console Application project to the solution.
   
   You can use either Visual Basic .NET or Visual C# .NET. Name the project Server.
6. In Solution Explorer, right-click Server and then click Add Reference.
7. In the Reference dialog box, click the Projects tab. Double-click InterfaceDLL and then click OK.
8. Replace the existing code with the following code:
   
   Visual Basic .NET Code

   Option Strict On
   Imports System
   Imports System.Runtime.Remoting
   Imports System.Runtime.Remoting.Channels
   Imports System.Runtime.Remoting.Channels.Tcp
   Imports System.Collections
   Imports System.Collections.Specialized
   Imports InterfaceDLL.test
   Imports InterfaceDLL.test.SystemSettingInterface
   
   Namespace test.server
      Public Class SystemSettingTest : Inherits MarshalByRefObject
         Implements ISystemSetting
   
         ' HashTable used for Enumeration
         Public Shared m_HashTable As Hashtable
         Private Shared m_initialized As Boolean
   
         Shared Sub Main()
            Dim m_systemSettingTest As SystemSettingTest = New SystemSettingTest()
            m_systemSettingTest.Init()
            Console.WriteLine("Test Server Running.")
            Console.ReadLine()
         End Sub
   
         Public Sub Test() Implements ISystemSetting.Test
            If IsNothing(m_HashTable) Then
               ' Create new instance the HashTable
               m_HashTable = New Hashtable()
   
               ' Add elements to the Hashtable
               m_HashTable.Add("testkey1", "testvalue1")
               m_HashTable.Add("testkey2", "testvalue2")
            End If
         End Sub
   
         Private Sub Init()
            Try
               ' Register Channel for Remoting
               ChannelServices.RegisterChannel(New TcpChannel(9999))
               RemotingConfiguration.RegisterWellKnownServiceType(GetType(SystemSettingTest), "SystemSettingTest", WellKnownObjectMode.SingleCall)
               m_initialized = True
   
            Catch ex As Exception
               m_initialized = False
               Throw New System.Exception("Unable to establish WKS: " + ex.Message)
            End Try
         End Sub
   
         ' Add method implementation 
         Public Sub Add(ByVal Key As Object, ByVal Value As Object) Implements ISystemSetting.Add
            m_HashTable.Add(Key, Value)
         End Sub
   
         ' Count method implementation
         Public ReadOnly Property Count() As Integer Implements ISystemSetting.Count
            Get
               Return m_HashTable.Count
            End Get
         End Property
   
         ' GetEnumerator method implementation. This method generates error
         Public Function GetEnumerator() As System.Collections.IEnumerator Implements ISystemSetting.GetEnumerator
            ' Return the Enumerator for the Hashtable
            Dim T As IDictionaryEnumerator = m_HashTable.GetEnumerator()
            Return T
         End Function
   
         ' This is the Workaround method that directly returns the Hashtable instead of Enumerator
         Public Function GetHashTable() As System.Collections.Hashtable Implements InterfaceDLL.test.SystemSettingInterface.ISystemSetting.GetHashTable
            Return m_HashTable
         End Function
   
         ' Item property method implementation
         Default Public Property Item(ByVal key As Object) As Object Implements ISystemSetting.Item
            Get
               Return m_HashTable(key)
            End Get
            Set(ByVal Value As Object)
            End Set
         End Property
   
      End Class
   
   End Namespace
   

   Visual C# .NET Code

   using System;
   using System.Runtime.Remoting;
   using System.Runtime.Remoting.Channels;
   using System.Runtime.Remoting.Channels.Tcp;
   using System.Collections;
   using System.Collections.Specialized;
   using test.SystemSettingInterface;
   using test;
   
   namespace test.server
   {
   	 
   	public class SystemSettingTest : MarshalByRefObject, ISystemSetting
   	{
   		static void Main(string[] args)
   		{
   			SystemSettingTest m_systemSettingTest = new SystemSettingTest();
   			m_systemSettingTest.Init();
   			Console.WriteLine ("Test Server Running.");
   			Console.ReadLine();
   		}
   
         // HashTable used for Enumeration
   		public static Hashtable m_HashTable;
   		
   		private static bool m_initialized;
   
   		public void Test()
   		{
   			if(m_HashTable==null)
   			{
   				// Create new instance the HashTable
   				m_HashTable= new Hashtable();
               
               // Add elements to the Hashtable
   				m_HashTable.Add("testkey1", "testvalue1");
   				m_HashTable.Add("testkey2", "testvalue2");
   			}
   		}
   		private void Init()
   		{
   			try
   			{
   			   // Register Channel for Remoting
               ChannelServices.RegisterChannel(new  TcpChannel(9999));
   				RemotingConfiguration.RegisterWellKnownServiceType(typeof(SystemSettingTest),
   					"SystemSettingTest", WellKnownObjectMode.SingleCall);
   					
   				m_initialized=true;
   			}
   			catch (System.Exception ex)
   			{
   				m_initialized=false;
   				throw new System.Exception("Unable to establish WKS: " + ex.Message);
   			}
   		}
         // Add method implementation
   		public void Add(object Key, object Value)
   		{
   			m_HashTable.Add(Key,Value);
   		}
   		
         // GetEnumerator method implementation. This method generates error
   		public IEnumerator GetEnumerator()
   		{
            // Return the Enumerator for the Hashtable
   			IDictionaryEnumerator T = m_HashTable.GetEnumerator();
            return T;
   		}
   
         // This is the Workaround method that directly returns the Hashtable instead of Enumerator
         public Hashtable GetHashtable()
         {
            return m_HashTable;
         }
   		
         // Default property for Enumeration
         public object this [object key]
   		{
   			get
   			{
   				return m_HashTable[(string)key];
   			}
   			set
   			{
   			}
   		}
   
         // Count property implementation
   		public int Count
   		{
   			get
   			{
   				return m_HashTable.Count;
   			}
   		}
   	}
   }
   

9. In Solution Explorer, right-click Server and then click Set as StartUp Project.
10. On the Debug menu, click Start.
11. Open a new instance of Visual Studio .NET development environment.
12. Create a new Windows application project.
    
    You can use either Visual Basic .NET or Visual C# .NET. Name the project Client.
13. In Solution Explorer, right-click Client and then click Add Reference.
14. Click Browse and then select InterfaceDLL.dll that you created in step 3.
15. Click OK to add the reference.
16. Replace the existing code with the following code:
    
    Visual Basic .NET Code

    Option Strict On
    
    Imports System.Net
    Imports System.Runtime.Remoting
    Imports System.Runtime.Remoting.Channels
    Imports System.Runtime.Remoting.Channels.Tcp
    Imports InterfaceDLL.test
    Imports InterfaceDLL.test.SystemSettingInterface
    
    Public Class Form1
       Inherits System.Windows.Forms.Form
    
    #Region " Windows Form Designer generated code "
    
       Public Sub New()
          MyBase.New()
    
          'This call is required by the Windows Form Designer.
          InitializeComponent()
    
          'Add any initialization after the InitializeComponent() call
    
       End Sub
    
       'Form overrides dispose to clean up the component list.
       Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
          If disposing Then
             If Not (components Is Nothing) Then
                components.Dispose()
             End If
          End If
          MyBase.Dispose(disposing)
       End Sub
    
       'Required by the Windows Form Designer
       Private components As System.ComponentModel.IContainer
    
       'NOTE: The following procedure is required by the Windows Form Designer
       'It can be modified using the Windows Form Designer.  
       'Do not modify it using the code editor.
       Friend WithEvents button3 As System.Windows.Forms.Button
       Friend WithEvents button2 As System.Windows.Forms.Button
       Friend WithEvents button1 As System.Windows.Forms.Button
       Friend WithEvents Button4 As System.Windows.Forms.Button
       <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
          Me.button3 = New System.Windows.Forms.Button()
          Me.button2 = New System.Windows.Forms.Button()
          Me.button1 = New System.Windows.Forms.Button()
          Me.Button4 = New System.Windows.Forms.Button()
          Me.SuspendLayout()
          '
          'button3
          '
          Me.button3.Location = New System.Drawing.Point(32, 106)
          Me.button3.Name = "button3"
          Me.button3.Size = New System.Drawing.Size(208, 32)
          Me.button3.TabIndex = 5
          Me.button3.Text = "GetEnumerator (Error)"
          '
          'button2
          '
          Me.button2.Location = New System.Drawing.Point(32, 61)
          Me.button2.Name = "button2"
          Me.button2.Size = New System.Drawing.Size(208, 32)
          Me.button2.TabIndex = 4
          Me.button2.Text = "Count Hashtable elements"
          '
          'button1
          '
          Me.button1.Location = New System.Drawing.Point(32, 16)
          Me.button1.Name = "button1"
          Me.button1.Size = New System.Drawing.Size(208, 32)
          Me.button1.TabIndex = 3
          Me.button1.Text = "Initialize Remote Component"
          '
          'Button4
          '
          Me.Button4.Location = New System.Drawing.Point(32, 151)
          Me.Button4.Name = "Button4"
          Me.Button4.Size = New System.Drawing.Size(208, 32)
          Me.Button4.TabIndex = 6
          Me.Button4.Text = "GetHashtable (Work around)"
          '
          'Form1
          '
          Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
          Me.ClientSize = New System.Drawing.Size(280, 206)
          Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.Button4, Me.button3, Me.button2, Me.button1})
          Me.Name = "Form1"
          Me.Text = "Form1"
          Me.ResumeLayout(False)
    
       End Sub
    
    #End Region
       Private m_SystemSetting As ISystemSetting
    
       ' Connect to server using Remoting
       Private Sub init()
          Dim connect As String = "tcp://" + Dns.GetHostName() + ":9999/SystemSettingTest"
          m_SystemSetting = CType(RemotingServices.Connect(GetType(ISystemSetting), connect), ISystemSetting)
          m_SystemSetting.Test()
       End Sub
    
       ' Initialize the Hashtable
       Private Sub button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles button1.Click
          Try
             init()
             MessageBox.Show("Init success.")
          Catch ex As Exception
    
             MessageBox.Show("Unable to initialize remoting connection with test server:" + ex.Message)
          End Try
       End Sub
    
       ' Verify the Hashtable has elements
       Private Sub button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles button2.Click
          Try
             MessageBox.Show(m_SystemSetting.Count.ToString())
          Catch ex As Exception
             MessageBox.Show(ex.Message)
          End Try
       End Sub
    
       ' Problem method call
       Private Sub button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles button3.Click
          ' Get the Enumerator for Hashtable
          Dim T As IDictionaryEnumerator = CType(m_SystemSetting.GetEnumerator(), IDictionaryEnumerator)
          MessageBox.Show(T.Value.ToString())
       End Sub
    
       ' Work Around method call
       Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
          Dim ht As Hashtable
          ht = m_SystemSetting.GetHashTable()
          Dim obj As Object
          For Each obj In ht.Values
             MessageBox.Show(obj.ToString())
          Next
       End Sub
    End Class
    

    Visual C# .NET Code

    using System;
    using System.Net;
    using System.Drawing;
    using System.Collections;
    using System.Collections.Specialized;
    using System.ComponentModel;
    using System.Windows.Forms;
    using System.Runtime.Remoting;
    using System.Runtime.Remoting.Channels;
    using System.Runtime.Remoting.Channels.Tcp;
    using test.SystemSettingInterface;
    
    namespace test.client
    {
       public class Form1 : System.Windows.Forms.Form
       {
          private ISystemSetting m_SystemSetting;
          private System.Windows.Forms.Button button1;
          private System.Windows.Forms.Button button2;
          private System.Windows.Forms.Button button3;
          private System.Windows.Forms.Button button4;
          private System.ComponentModel.Container components = null;
    
          public Form1()
          {
             InitializeComponent();
    
          }
    
          protected override void Dispose( bool disposing )
          {
             if( disposing )
             {
                if (components != null) 
                {
                   components.Dispose();
                }
             }
             base.Dispose( disposing );
          }
    
    		#region Windows Form Designer generated code
          /// <summary>
          /// Required method for Designer support - do not modify
          /// the contents of this method with the code editor.
          /// </summary>
          private void InitializeComponent()
          {
             this.button1 = new System.Windows.Forms.Button();
             this.button2 = new System.Windows.Forms.Button();
             this.button3 = new System.Windows.Forms.Button();
             this.button4 = new System.Windows.Forms.Button();
             this.SuspendLayout();
             // 
             // button1
             // 
             this.button1.Location = new System.Drawing.Point(32, 16);
             this.button1.Name = "button1";
             this.button1.Size = new System.Drawing.Size(208, 32);
             this.button1.TabIndex = 0;
             this.button1.Text = "Initialize Remote Component";
             this.button1.Click += new System.EventHandler(this.button1_Click);
             // 
             // button2
             // 
             this.button2.Location = new System.Drawing.Point(32, 58);
             this.button2.Name = "button2";
             this.button2.Size = new System.Drawing.Size(208, 32);
             this.button2.TabIndex = 1;
             this.button2.Text = "Count Hashtable elements";
             this.button2.Click += new System.EventHandler(this.button2_Click);
             // 
             // button3
             // 
             this.button3.Location = new System.Drawing.Point(32, 100);
             this.button3.Name = "button3";
             this.button3.Size = new System.Drawing.Size(208, 32);
             this.button3.TabIndex = 2;
             this.button3.Text = "GetEnumerator (Error)";
             this.button3.Click += new System.EventHandler(this.button3_Click);
             // 
             // button4
             // 
             this.button4.Location = new System.Drawing.Point(32, 142);
             this.button4.Name = "button4";
             this.button4.Size = new System.Drawing.Size(208, 32);
             this.button4.TabIndex = 3;
             this.button4.Text = "GetHashtable (work around)";
             this.button4.Click += new System.EventHandler(this.button4_Click);
             // 
             // Form1
             // 
             this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
             this.ClientSize = new System.Drawing.Size(280, 198);
             this.Controls.AddRange(new System.Windows.Forms.Control[] {
                                                                          this.button4,
                                                                          this.button3,
                                                                          this.button2,
                                                                          this.button1});
             this.Name = "Form1";
             this.Text = "Form1";
             this.ResumeLayout(false);
    
          }
    		#endregion
    
          [STAThread]
          static void Main() 
          {
             Application.Run(new Form1());
          }
    
          // Initialize the Hashtable
          private void button1_Click(object sender, System.EventArgs e)
          {
    
             try
             {
                init();
                MessageBox.Show("Init success.");
             }
             catch(System.Exception ex)
             {
                MessageBox.Show("Unable to initialize remoting connection with test server:" + ex.Message);
             }
    			
          }
    
          // Connect to server using Remoting
          private void init()
          {
             string connect="tcp://" + Dns.GetHostName() + ":9999/SystemSettingTest";
             m_SystemSetting=(ISystemSetting)RemotingServices.Connect(typeof(ISystemSetting), connect);
             m_SystemSetting.Test();
    		
          }
    
          // Verify the Hashtable has elements
          private void button2_Click(object sender, System.EventArgs e)
          {
             try
             {
                MessageBox.Show(this.m_SystemSetting.Count.ToString());
             }
             catch(System.Exception ex)
             {
                MessageBox.Show(ex.Message);
             }
    			
          }
    
          // Problem method call
          private void button3_Click(object sender, System.EventArgs e)
          {
             IDictionaryEnumerator T = (IDictionaryEnumerator)m_SystemSetting.GetEnumerator();
             // Get the Enumerator for Hashtable
             MessageBox.Show(T.Value.ToString());
          }
    
          // Work Around method call
          private void button4_Click(object sender, System.EventArgs e)
          {
             Hashtable ht;
             ht=m_SystemSetting.GetHashtable();
             foreach(Object obj in ht.Values)
             {
                MessageBox.Show(obj.ToString());
             }
          }
       }
    }
    

17. On the Debug menu, click Start.
18. Click Initialize Remote Component. Click OK to close the Init success dialog box.
19. Click Count Hashtable elements.
    
    You see 2 appear.
20. Click GetEnumerator (Error).
    
    You receive the error in the "Symptoms" section.
21. If you click GetHashtable (work around) after step 18, you can successfully iterate through the Hashtable.