SAMPLE: Enable Default Processing in a Subclassed Button Control

• Microsoft Visual C++, 32-bit Editions, version 5.0

SUMMARY

This article describes how to ensure default command processing when subclassing the standard Windows Button control to create an MFC ActiveX control. It also discusses how to determine when a control is the default command in both design- and run-time modes so that the control is drawn correctly. Finally, the article addresses how to ensure that the ENTER key gets routed to the current default command.

MORE INFORMATION

The following file is available for download from the Microsoft Software Library:

 ~ DefButn.exe (size: 36114 bytes) 

   ARTICLE-ID: Q119591
   TITLE     : How to Obtain Microsoft Support Files from Online Services

• Make a Subclassed Control That Supports Extended Properties
• Set a Control to Be the Default Command at Run Time
• Use the Caption Property to Display the Command Text
• Draw Correctly Depending Upon Default Command Status
• Ensure That the ENTER Key Gets Routed to the Current Default Command

Make a Subclassed Control That Supports Extended Properties

To create a control that supports extended properties so that the container can display its extended Default property in the Property Browser window when the control is selected at design time, do the following:

1. Use the MFC ActiveX ControlWizard in Microsoft Visual C++ to create a new project called DefBtn.

2. Accept all defaults in step 1.

3. In step 2, select the Button control in response to “Which window class, if any, should this control subclass?” and accept all other defaults.

4. Click Finish to create the control.

5. In DefBtnctl.cpp add the following miscellaneous status bit to the _dwDefBtnOleMisc bit mask:

         OLEMISC_ACTSLIKEBUTTON
   

   This allows a container that supports extended properties, such as Visual Basic, to present the Default extended property in its Property Browser window during design time. When using the control in an application, a programmer can make your control the default command by setting this property to “True.” Note that in an environment that does not support extended properties, such as Visual C++, this flag has no effect.

Set a Control to Be the Default Command at Run Time

To set the default command at run time in an MFC dialog-based container application that does not support extended properties, add the following call to the OnInitDialog processing:

   CDialog::SetDefID

Use the Caption Property to Display the Command Text

To display the command text both at run time and design time, do the following:

1. Expose the stock Caption property using ClassWizard. The subclassed control automatically draws this property at run time.

2. To display the text at design time you have to include drawing code in the CDefBtnCtrl::OnDraw member function to check whether the UserMode ambient property is set to “False” (indicating design mode).

3. Use the CDC::GetInternalText member function to get the current value of the Caption stock property and draw it using the CDC::DrawText member function.

Draw Correctly Depending Upon Default Command Status

ActiveX controls implement functionality that the older, pre-Ole Windows controls (such as the Button control) do not. Because the MFC method of subclassing a control is a way to support older technology, there tend to be inconsistencies in certain operations (especially drawing) between subclassed controls and those developed without subclassing. For example, the Button control does not draw its border in accordance with Windows 95 user interface guidelines for a default command.

You can add logic to a subclassed control so that its border is drawn to reflect the default command status. Look at various CDC member functions such as DrawEdge to do so. Note that the DefButn.exe sample does not include the code to do this.

The DefButn.exe sample does include the logic to detect any change in the default command status when overriding the CDefBtnCtrl::OnAmbientPropertyChange member function. To determine when a control has been set as the default command on a form at design time, and to draw correctly depending upon the default command status in both design- and run-time modes, do the following:

1. If the DISPID of the ambient property passed in is:

         DISPID_AMBIENT_DISPLAYASDEFAULT
   

   then obtain the value it changed to by calling the GetAmbientProperty function.

2. Pass in this DISPID and the address of a BOOL class member variable called m_bDefault. If “True,” the control becomes the default button; “False” means it is no longer the default button.

3. Call the InvalidateControl function to redraw the control (use CDefBtnCtrl::OnDraw) with the shadow outline border that indicates that a command is the default. Use the value of m_bDefault to determine whether you should draw the outline (True) or remove it (False).

Ensure That the ENTER Key Gets Routed to the Current Default Command

This section describes how to receive the WM_COMMAND message when the ENTER key is pressed, and the default command is a subclassed control. In Microsoft Visual C++ Books Online, "Programming with MFC: Encyclopedia," the article called "Keyboard Interface" contains the following paragraph:

   The container traps the ENTER and ESC keys by including them in its
   accelerator table. When one of these keys is pressed, the container
   calls the standard method Click in the appropriate control's primary
   dispatch interface. The standard Click method is described in Control
   Methods.

If no special processing is needed and you just want to ensure that the Click event gets fired back to the container, then expose the DoClick stock method and the Click stock event. In MFC's default processing, FireClick will be called for you.