PRB: MFC Control Does Not Detect Keystrokes When SSTabs Exist

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

SYMPTOMS

An MFC-based ActiveX control cannot gain input focus when an SSTab control is on the same form. This only happens when you click the MFC control (at which time the MFC control should get the input focus) right after you have clicked one of the SSTab's tab pages. The control works as expected when there is no SSTab on the form or when you click the MFC control after clicking other controls, such as the Visual Basic intrinsic TextBox. As an example, if the MFC control aggregates a child Edit box control, and if you click it right after you've clicked the SSTab's tab page, nothing can be typed into your MFC control's Edit box.

CAUSE

MFC ActiveX controls UI-Activate themselves when they receive the mouse- click message. If you have a child control inside your COleControl, mouse- click messages on the child control are not sent to the COleControl and MFC does not UI-Activate the ActiveX control, even though the child control has just been given the keyboard focus. When the SSTab gets the focus, your control needs to explicitly UI-Activate itself to actually get the input focus when you click the control.

RESOLUTION

There are two ways to resolve the problem. The first method needs to change the MFC control's source code. The idea is to UI-Activate the whole control whenever your control is activated. Usually, this is done with an event handler, such as the following:

   int CMyEditCtlAppCtrl::OnMouseActivate(CWnd* pDesktopWnd,
             UINT nHitTest, UINT message)
   {
      OnActivateInPlace (TRUE, NULL); // UI-Activate the control
      return COleControl::OnMouseActivate(pDesktopWnd, nHitTest, message);
   } 

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Create an MFC ActiveX Control with an Edit Child Control

1. Open Visual C++. Select New from the File menu. Create a new MFC ActiveX control wizard project. Use MyEditCtlApp as the project's name and accept all the default settings. Click "finish" to actually create the project.



2. Add a contained Edit control object to the control by adding the following lines to the MyEditCtlAppCtl class declaration in the MyEditCtlAppCtl.h file:

   
         private:
            CEdit m_Edit; 




3. Add the following line to the MyEditCtlAppCtl class declaration in the MyEditCtlAppCtl.h file to provide OnCreate message handling function:

   
         afx_msg int OnCreate(LPCREATESTRUCT lpCreateStruct); 




4. Add the following line to the MessageMap (within BEGIN_MESSAGE_MAP and END_MESSAGE_MAP pair) in MyEditCtlAppCtl.cpp file:

   
         ON_WM_CREATE() 




5. Add the following lines to the MyEditCtlAppCtl.cpp file to implement the OnCreate function:

   
         int CMyEditCtlAppCtrl::OnCreate(LPCREATESTRUCT lpCreateStruct)
         {
            // Call the base class's OnCreate
            if (COleControl::OnCreate(lpCreateStruct) == -1)
              return -1;
   
            // Create the edit control
            CRect rClient;
            CString strTemp = "";
            GetClientRect(rClient);
            m_Edit.Create(WS_CHILD | WS_VISIBLE | WS_VSCROLL | WS_OVERLAPPED |
                   WS_CLIPSIBLINGS | ES_MULTILINE | ES_WANTRETURN,
                   rClient, this, 123L);
            m_Edit.SetWindowText(strTemp);
            return 0;
          } 




6. Build the project by pressing the F7 key or selecting "Build MyEditCtlApp.ocx" from the Build menu and the control will be automatically registered.

Steps to Create a Visual Basic Test Project

1. Open Visual Basic and create a Visual Basic standard EXE project. Form1 is created by default.



2. Choose "Components" from the Project menu to bring up the project components dialog. Find "MyEditCtlApp ActiveX Control Module" in the list and select the checkbox beside of it. Click on the "Apply" button and a new icon with "ocx" will be added to the tool box. You may then close the components dialog.



3. Add a MyEditCtlApp control to the form.



4. Run the application. You can click the control and type in characters without problem.



5. Stop the application.



6. Choose "Components" from the Project menu to bring up the project components dialog. Find "Microsoft Tabbed Dialog Control 6.0" in the list and select the checkbox beside of it. Click on the "Apply" button and an icon for the tab control will be added to the tool box. You can then close the components dialog.



7. Put an SSTab control to the form and enlarge it so that it can hold other controls.



8. Put a MyEditCtlApp controls on SSTab tab0 and tab1.



9. Run the application. Now, if you click the SSTab control's tab0, tab1, etc., and then click any MyEditCtlApp control, you cannot type in any characters. This is the problem.

Steps to Fix the Problem in C++

1. Open the MyEditCtlApp project in Visual C++.



2. Add the following line to the MyEditCtlAppCtl class declaration in the MyEditCtlAppCtl.h file to overload the OnMouseActivate virtual function:

   
         virtual int OnMouseActivate(CWnd* pDesktopWnd, UINT nHitTest, UINT); 




3. Add the following line to the MessageMap (within BEGIN_MESSAGE_MAP and END_MESSAGE_MAP pair) in MyEditCtlAppCtl.cpp file:

   
         ON_WM_MOUSEACTIVATE() 




4. Add the following lines to the MyEditCtlAppCtl.cpp file to implement the OnMouseActivate function:

   
         int CMyEditCtlAppCtrl::OnMouseActivate(CWnd* pDesktopWnd,
                  UINT nHitTest, UINT message)
         {
            OnActivateInPlace (TRUE, NULL); //UI-Activate the control
            return COleControl::OnMouseActivate(pDesktopWnd,
                       nHitTest, message);
         } 




5. Rebuild the project and run the Visual Basic test project. This time, everything works as expected.

Steps to Fix the Problem in Visual Basic

1. Open the Visual Basic test project with the old MFC control.



2. Add the following code to the form's code window where MyEditCtlApp2 can be replaced with any MyEditCtlApp control placed on Tab control:

   
         Private Sub SSTab1_Click(PreviousTab As Integer)
            MyEditCtlApp2.SetFocus
         End Sub 




3. Run the application and note that everything works as expected.

Additional query words:

Keywords : kbActiveX kbCtrl kbVBp kbVBp600 kbVC kbGrpVB kbCodeSam kbMFC600
Version : WINDOWS:6.0
Platform : WINDOWS
Issue type : kbprb