BUG: Error 424 Adding Data Object Wizard-Created Ctrl to Form

MORE INFORMATION

The steps below describe how to reproduce and correct this behavior. The steps are broken up into sections that you need to follow in sequence. Note that while it is necessary to create a Data Environment and a Class object, the details of their creation are not directly related to the behavior described.

This example creates a UserControl based on a ListBox. The information in the article is also relevant if the UserControl is based on a ComboBox. Some details, such as the names of objects created by the Data Object Wizard, will vary in the latter case.

Creating a Data Environment Object

1. Start Visual Basic 6.0.
2. Create a new Standard EXE project. Form1 is created by default.
3. From the Project menu, click Add Data Environment.
4. Right-click Connection1 in the Data Environment, and click Properties.
5. In the Data Link Properties dialog box, set the following properties, test the connection, and then click OK:
   
   
   • On the Provider tab, select the Microsoft Jet 3.51 OLE DB Provider option.
   • On the Connection tab, select nwind.mdb, which is in the same directory as Visual Basic, as the Database name.
6. In the Data Environment, right-click Connection1 and click Add Command.
7. Right-click Command1, and click Properties.
8. In the Command1 Properties dialog box, set the following properties and click OK:
   
   
   • On the General tab, click the Table option for the Database Object.
   • On the General tab, click the Products option for the Object Name.

Creating a Class Object

1. From the Add-Ins menu, click VB 6 Data Object Wizard.
   
   NOTE: If this option does not appear on the menu, load the Wizard using the Add-In Manager and make sure to select the Loaded/Unloaded check box.
2. If the Introduction dialog box of the wizard appears, click Next.
3. In the Create Object dialog box of the wizard, click Next.
4. In the Select Data Environment Command dialog box of the wizard, click Command1 and click Next.
5. Click Next on each dialog box until you reach the Finish dialog box.

Creating a User Control

The following steps describe how to create a user control, which exposes the problem described in this article.

1. In the Finish dialog box of the wizard, enter "MyClass" (no quotes) as the name for the Class object you are creating, and click Finish.
2. From the Add-Ins menu, click VB 6 Data Object Wizard.
3. If the Introduction dialog box of the wizard appears, click Next.
4. In the Create Object dialog box of the wizard, click the option to create "A User Control object bound to an existing Class object" and click Next.
5. In the Select the Data Class to Use dialog box of the wizard, select rsclsMyClass and click Next.
6. In the Select User Control Type dialog box of the wizard, select ListBox and click Next.
7. In the Map Class Properties to a Control Type dialog box of the wizard, click Next.
8. In the Enter User Control Name dialog box of the wizard, enter "MyControl" (no quotes) as the User Control Name and click Finish.

Placing the User Control on the Form

1. Close the design window for the newly-created UserControl.
   
   NOTE: It will be titled "Project1 - uctMyControlListBox (UserControl)". You must close it before you can place it on a form.)
2. You have to add the UserControl to the Toolbox. Place this control on Form1. (Form1 is created by default when the project was initially created.)

RESULT: Run Time Error 424 (Object required) occurs.

Resolving the Problem

1. Click the Debug button on the error dialog box.
2. Notice that the highlighted line of code that caused the error is in the UserControl's Resize event procedure and refers to lstMyControl. There are also three additional references to lstMyControl in this procedure.
3. From the Run menu, click End.
4. In the UserControl's Resize event procedure, change the references to lstMyControl to lstMyClass.
5. Again, try to place the UserControl on Form1.

RESULT: The control is placed successfully.