HOWTO: Create Data Bound Controls

• Microsoft Visual Basic Professional and Enterprise Editions, for Windows, version 5.0

SUMMARY

Visual Basic allows a user's custom ActiveX control to have properties that are “bound” to database fields. This article describes how to bind these properties.

MORE INFORMATION

When defining a bindable property for a control, do the following:

1. With the code window of your custom ActiveX control visible, click Procedure Attributes from the Tools menu.

2. Click Advanced.

3. In the Name field, select the property you want to be bindable.

1. Property binds to DataField.

   This means that the DataField property, exposed at design-time, will define the database field for which this property is bound. Only one property can use the DataField property to bind to a database field. If you have many bindable properties, you must use the DataBindings collection (see next option).

2. Show in DataBindings collection at design-time.

   This exposes a DataBindings property at design-time. When used, this property displays a dialog that allows you to choose which bindable properties are bound to which database fields.

3. Property will call CanPropertyChange before changing.

   The CanPropertyChange function asks the container if a property bound to a data source can be changed.

Step-by-Step Example

The following example creates a custom ActiveX control with two bindable properties:

1. Start a new ActiveX Control project. UserControl1 is added by default.

2. Add two Textbox controls, Text1 and Text2, to UserControl1.

3. Add the following code to the General Declarations of the UserControl1 section:

         Option Explicit
   

         Private Sub UserControl_Initialize()
            Text1.Text = "Caption"
            Text1.Left = 0
            Text2.Text = "Subcaption"
            Text2.Left = 0
            Text2.Font.Name = "Arial"
            Text2.Font.Size = 7
         End Sub
   
         Private Sub UserControl_ReadProperties(PropBag As PropertyBag)
            Caption = PropBag.ReadProperty("Caption", "")
            SubCaption = PropBag.ReadProperty("SubCaption", "")
         End Sub
   
         Property Let Caption(strNewValue As String)
            If CanPropertyChange("Caption") Then
               Text1.Text = strNewValue
               PropertyChanged "Caption"
            End If
         End Property
   
         Property Get Caption() As String
            Caption = Text1.Text
         End Property
   
         Property Let SubCaption(strNewValue As String)
            If CanPropertyChange("SubCaption") Then
               Text2.Text = strNewValue
               PropertyChanged "Caption"
            End If
         End Property
   
         Property Get SubCaption() As String
            SubCaption = Text2.Text
         End Property
   
         Private Sub UserControl_WriteProperties(PropBag As PropertyBag)
            PropBag.WriteProperty "Caption", Caption, ""
            PropBag.WriteProperty "SubCaption", SubCaption, ""
         End Sub
   
         Private Sub Text1_Change()
            PropertyChanged "Caption"
         End Sub
   
         Private Sub Text2_Change()
            PropertyChanged "SubCaption"
         End Sub
   
   

4. To make the properties "Caption" and "SubCaption" bindable, click Procedure Attributes from the Tools menu.

5. Select "Caption" from the Name field, and the click Advanced.

6. Select the "Property is data bound" option.

7. Select the "Show in DataBindings collection at design-time" option.

8. Select the "Property will call CanPropertyChange before changing" option.

9. Select the "This property binds to DataField" option.

10. Click Apply.

11. Repeat steps 6 to 8 for the "SubCaption" property, and click Apply.

        Do not repeat step 9 as only one property can be bound to the
        DataField.
    

12. Click OK.