HOWTO: Use the HitTest Event and HitBehavior Property

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, version 6.0

SUMMARY

This article discusses a new Event-Property pair available for UserControls created using Visual Basic 6.0. The general purpose of the HitTest Event, and the HitBehavior Property is to give greater flexibility in responding to UserControl events. Specifically, this article demonstrates how to build a transparent UserControl that responds to mouse events. This was not possible in previous versions of Visual Basic.

MORE INFORMATION

Using HitTest is relatively straightforward. "HitResult" is a value that is passed into the HitTest event by the system. By examining the value of HitResult, you can determine on which area of the control the mouse event occurred. Based on that information, you can reset the value of HitResult to have the control respond in the desired manner. You can instruct the control to process the mouse event, or you can instruct the control to pass the event on to the container. The default settings for the HitBehavior Property do not need to be changed for these examples.

For the examples used here, there are two different scenarios depending on whether or not the UserControl has been masked using MaskPicture and MaskColor. If your UserControl does not have a masked area please see the section entitled "Capturing Mouse Events on a Transparent UserControl." If your UserControl has a masked area, please see the section entitled "Capturing Mouse Events on a Masked Usercontrol."

It is important to note that the HitTest event occurs only on a Windowless UserControl with the BackStyle property set to Transparent. Windowless UserControls are also new to Visual Basic 6.0.

Capturing Mouse Events on a Transparent UserControl

1. Create a New Standard EXE project.



2. Add a UserControl to the project. (You may receive a warning that the UserControl can not be Public in this type of project. Choose OK in response to this message.)



3. Set the BackStyle property of the UserControl to Transparent.



4. Set the Windowless property of the UserControl to True.



5. Add the following code to the UserControl's module:

   
         Private Sub UserControl_Click()
            Debug.Print "Usercontrol Click"
         End Sub
   
         Private Sub UserControl_DblClick()
            Debug.Print "Usercontrol Doubleclick"
         End Sub
   
         Private Sub UserControl_HitTest(X As Single, Y As Single, _
                                             HitResult As Integer)
   
            'Instruct the UserControl to behave as if the click occurred on a
            ' painted region of the control.
            If HitResult = vbHitResultOutside Then
               HitResult = vbHitResultHit
            End If
   
         End Sub
    




6. Place the UserControl on Form1. You may wish to draw a rectangle or other shape around the control since the control will not be visible.



7. Run the project.



8. Clicking or double-clicking the UserControl should result in the display of the message boxes.

Capturing Mouse Events on a Masked UserControl

1. Create a bitmap with a white background that contains a filled red circle.



2. Perform steps 1-4 from the previous section.



3. Set the following properties for the UserControl:

   
         BackStyle:      0 - Transparent
         MaskColor:      &H00FFFFFF&  'White
         MaskPicture:    The bitmap created in Step 1.
         BackColor:      &H000000FF& 'Red
    




4. Add the following code to the UserControl:

   
         Private Sub UserControl_Click()
            Debug.Print "Usercontrol Click"
         End Sub
    




5. Add the following code to Form1:

   
         Private Sub Form_Click()
            Debug.Print "Form Click"
         End Sub
    




6. Run the project. Click the masked (or visible) portion of the UserControl. You should see the "UserControl Click" message box. Clicking the transparent area of the control should cause the "Form Click" message box to display. This is the default behavior of a masked control - events on the painted area will be processed by the control and events on the transparent area will be forwarded to the container.



7. The event process behavior can be modified at this point to create separate responses based on which area of the UserControl received the Mouse event.



8. Add the following code to the General Section of the UserControl's module:

   
         Private HitTestFlag As Integer
   
         Private Sub UserControl_HitTest(X As Single, Y As Single, _
                                             HitResult As Integer)
            HitTestFlag = HitResult
            'Set the UserControl to respond to the event.
            HitResult = vbHitResultHit
         End Sub
    




9. Replace the UserControl_Click event created in step 2 with the following:

   
         Private Sub UserControl_Click()
            If HitTestFlag = vbHitResultOutside Then
               Debug.Print "usercontrol transparent area click"
            ElseIf HitTestFlag = vbHitResultHit Then
               Debug.Print "usercontrol painted area click"
            End If
         End Sub
    




10. Run the project. Clicking the Masked area of the control should display the "painted area click" message. Clicking the transparent area of the control should display the "transparent area click" message.

Using X and Y Coordinates with HitTest

1. Start a new Standard EXE project in Visual Basic 6.0.



2. Add a Usercontrol to the project.



3. Set the Windowless property of the UserControl to True.



4. Set the BackStyle property of the UserControl to Transparent.



5. Add the following code to the UserControl module:

   
         Private Sub UserControl_HitTest(X As Single, Y As Single, _
                                             HitResult As Integer)
   
         Dim txtDisplay As String
         With UserControl
            If Y < .Height / 2 Then
               txtDisplay = "Upper "
            Else
               txtDisplay = "Lower "
            End If
            If X < .Width / 2 Then
               txtDisplay = txtDisplay & "Left"
            Else
               txtDisplay = txtDisplay & "Right"
            End If
         End With
   
         Parent.Label1.Caption = txtDisplay
   
         End Sub
    




6. Add a Label to the Form.



7. Add the UserControl to Form1. You may wish to draw a square or rectangle around the control since it will not be visible. You may also want to display a picture on the form using the form's Picture property.



8. Set the BackStyle of the Label to Transparent.



9. Run the Project. As you move the mouse over the UserControl, the text in the Label control changes as you move from one quadrant to another.

The HitBehavior Property

Summary

REFERENCES

For additional information on using the MaskPicture and MaskColor properties, please see the following article(s) in the Microsoft Knowledge Base:

Q174216 : TransparentPaint Backstyle Option Unavailable

Additional query words: kbDSupport kbDSD kbCtrlCreate kbVBp600 kbVBp

Keywords : kbGrpVB
Version :
Platform : WINDOWS
Issue type : kbhowto