PRB: Problems Using Subclassed TreeView MFC Control in VB

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, versions 5.0, 6.0
• Microsoft Visual C++, 32-bit Editions, versions 5.0, 6.0

SYMPTOMS

You create a TreeView subclassed control using C++ with MFC ActiveX control Wizard. It works correctly in the MFC container, but when used in the VB container, the background color behind the "+", "-", and dotted lines is the container's background color rather than the TreeView control's background color. Further, when the VB project is compiled and run, an error message is generated indicating that the control can not be created and the application terminates.

CAUSE

The cause for the first problem is that the TreeView control creates bitmaps for the "+", "-", and dotted line when the control is first created. These bitmaps are used if the background color is not changed. When VB is used as the container, the TreeView control uses the container's back color as the default color.

The cause of the second problem is that the "SysTreeView32" window class needs to be registered before it can be created. A VB application won't register it automatically.

RESOLUTION

To fix the first problem, set the TreeView control's back color after the "SysTreeView32" window is created so that the bitmaps for "+", "-", and dotted lines are regenerated.

To fix the second problem, call "InitCommonControls()" before calling "COleControl::OnCreate(lpCreateStruct)" to create the window.

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Behavior

Steps to create a TreeView subclassed control with VC++

1. In VC++ Create a MFC ActiveX control Wizard project with project name "MyTreeView". Choose "SysTreeView32" as the class you want to subclass in the second step and keep all other settings as it is. Press "Finish".



2. Go to the following function in the MyTreeViewCtrl.cpp file:

   
         BOOL CMyTreeViewCtrl::PreCreateWindow(CREATESTRUCT& cs)
    

   Add the following line:

   
         cs.style |= TVS_EDITLABELS | TVS_HASBUTTONS | TVS_HASLINES;
    

   before this line:

   
         return COleControl::PreCreateWindow(cs);
    




3. In Class view, right click CMyTreeViewCtrl and select "Add Member Function" from the popup menu. Type HTREEITEM in the Function Type field, place the following text in the Function Declaration field, and click "OK".

   
      TreeInsertItem(const TCHAR* name,HTREEITEM hParent,HTREEITEM
                     hInsertAfter)
    




4. Replace the TreeInsertItem function in MyTreeViewCtrl.cpp with:

   
         HTREEITEM CMyTreeViewCtrl::TreeInsertItem(const TCHAR* name,
               HTREEITEM hParent,HTREEITEM hInsertAfter)
         {
            TV_ITEM item;
            TCHAR szName[256];
   
            item.mask = TVIF_TEXT;
            _tcsncpy(szName, name, 255);
            item.pszText=szName;
   
            TV_INSERTSTRUCT tsInsert;
            tsInsert.hParent=hParent;
            tsInsert.hInsertAfter=hInsertAfter;
            tsInsert.item=item;
   
            return TreeView_InsertItem(m_hWnd,&tsInsert);
         }
    




5. Select the View / Class Wizard menu option and click "Message Maps" tab. Select "CMyTreeViewCtrl" as the class name. Double click "WM_CREATE" in the "Messages" list box and click OK to ad the OnCreate message handler to the CMyTreeViewCtrl class.



6. In CMyTreeViewCtrl.cpp change the CMyTreeViewCtrl::OnCreate function to:

   
         int CMyTreeViewCtrl::OnCreate(LPCREATESTRUCT lpCreateStruct)
   
         {
            if (COleControl::OnCreate(lpCreateStruct) == -1)
               return -1;
   
            HTREEITEM root=TreeInsertItem(_T("Root"),TVI_ROOT,TVI_LAST);
            HTREEITEM sub1=TreeInsertItem(_T("sub1"),root,TVI_LAST);
            HTREEITEM subsub1=TreeInsertItem(_T("subsub2"),sub1,TVI_LAST);
            TreeInsertItem(_T("sub2"),root,TVI_LAST);
            return 0;
         }
    




7. Build the project and the control will be registered automatically.

Steps to create a VB sample

1. Create a Visual Basic Standard EXE project. Form1 is created by default.



2. Select Components from the Project menu, check "MyTreeView ActiveX Control module" and click OK.



3. Add a MyTreeViewCtrl control to Form1.



4. Press "F5" to run the application and double click on 'Root'. When you expand the + signs, you will observe the background color difference.



5. Compile the application to EXE and run the exe file. You will get a "Debug Assertion Error" message and your application will terminate.

Steps to Correct the Problems

1. Return to the MFC ActiveX control, "MyTreeView".



2. In the function CMyTreeViewCtrl::OnCreate in MyTreeViewCtrl.cpp replace the line:

   
            if (COleControl::OnCreate(lpCreateStruct) == -1)
               return -1;
    

   with the following:

   
            ::InitCommonControls();
   
            if (COleControl::OnCreate(lpCreateStruct) == -1)
               return -1;
   
            SendMessage(TVM_SETBKCOLOR, 0, (LPARAM)RGB(255,255,255));
            SendMessage(TVM_SETIMAGELIST , TVSIL_NORMAL , 0);
    




3. Rebuild the project.



4. Run the VB sample again and observe that everything works correctly.

Additional query words: kbDSupport kbDSD

Keywords : kbActiveX kbCtrl kbMFC kbVBp500 kbVBp600 kbVC500 kbVC600 kbGrpVB
Version : WINDOWS:5.0,6.0; WINNT:5.0,6.0
Platform :
Issue type :