FIX: The Load event does not execute when you use the ShowDialog method to show a form that contains an ActiveX control (318386)

MORE INFORMATION

This problem occurs when you show a form under the following two conditions:

1. When you show the form modally by using the ShowDialog method.
2. When the form is host to an ActiveX control.

NOTE: The following steps demonstrate this problem by using Visual Basic .NET. However, this behavior occurs at the Windows Forms level, so the behavior occurs regardless of the programming language that you use.

Steps to reproduce the behavior

NOTE: To perform the steps in the "Sample Resolution" section, you must first perform the steps in this section because the example in "Sample Resolution" uses the sample application that you create in this section.

To create a sample application that reproduces the behavior, follow these steps:

1. Create a new Visual Basic .NET Windows application. Form1 is created by default.
2. Add a command button to Form1.
3. Paste the following sample code in the Click event procedure for the button:

   Dim f As New Form2()
   
   f.ShowDialog()
   					

4. On the Project menu, click Add Windows Form and follow the onscreen instructions to add Form2 to the project.
5. On the Tools menu, click Customize Toolbox to add a reference to an ActiveX control, such as Microsoft Windows Common Dialog.
   
   NOTE: This example uses Microsoft Windows Common Dialog. However, you can use any ActiveX control to reproduce the behavior.
6. Place the referenced control on Form2.
7. Paste the following sample code in the Load event procedure of Form2:

   MessageBox.Show("Form2 Load Event")
   					

8. Run the sample and click the button on Form1. Form2 appears but the message box from the Load event procedure in Form2 does not appear.

Sample resolution

To override the window procedure of the form, you must specifically look for the WM_SHOWWINDOW message, and then manually call the method that you want. To override WNDPROC, follow these steps:

1. Paste the following sample code in the Form2 class of the application that you created in "Steps to Reproduce Behavior":

   Private Const WM_SHOWWINDOW = &H18
   Private m_loaded As Boolean
   
   Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)
      If m.Msg = WM_SHOWWINDOW Then
         If Not m_loaded Then
            MyBase.OnLoad(New System.EventArgs())
         End If
      End If
      MyBase.WndProc(m)
   End Sub
   					

2. Add the following sample code to the Load event procedure of Form2:

   m_loaded = True
   					

3. Run the sample, and then click the button on Form1. Form2 appears and the message box appears, which indicates that the Load event procedure executes.
   
   NOTE: The sample code adds the Boolean variable, m_loaded, which prevents the Load event procedure from running twice, in case the form is shown by using the Show method instead of by using the ShowDialog method.