DOCUMENT:Q141489 06-MAY-2001 [visualc] TITLE :INFO: Deriving an OLE Control from a Base Control PRODUCT :Microsoft C Compiler PROD/VER::4.0 OPER/SYS: KEYWORDS:kbcode kbfile kbsample kbActiveX kbCOMt kbCtrlCreate kbMFC kbVC400 kbGrpDSMFCATL kbArch ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - The Microsoft Foundation Classes (MFC), used with: - Microsoft Visual C++, 32-bit Editions, version 4.0 ------------------------------------------------------------------------------- This is the 32-bit version of this sample. SUMMARY ======= The Shapes32.exe sample illustrates deriving an OLE control from another. The following file is available for download from the Microsoft Software Library: Shapes32.exe (http://support.microsoft.com/download/support/mslfiles/Shapes32.exe) For more information about downloading files from the Microsoft Software Library, please see the following article in the Microsoft Knowledge Base: Q119591 How to Obtain Microsoft Support Files from Online Services MORE INFORMATION ================ The SHAPES32 sample illustrates deriving an OLE control from a base control, thus allowing the derived control to take advantage of the base control's methods, properties, and events. The SHAPES32 sample implements a base control class called CBaseShapeCtrl, and two derived control classes called CCircleCtrl and CRectangleCtrl. CCircleCtrl and CRectangleCtrl draw themselves using the properties provided by the base CBaseShapeCtrl class. CCircleCtrl and CRectangleCtrl also allow access to the methods and events implemented in the base CBaseShapeCtrl class. Properties, Methods, and Events ------------------------------- The CBaseShapeCtrl class provides the base functionality of a simple shape control. It implements the following properties, events, and methods: Name Type Use ------------ --------- --------------------------------------------------- FillColor Property An OLE_COLOR value which represents the color used to fill the shape. LineColor Property An OLE_COLOR value which represents the color used for the shape's outline. LineWidth Property A short value which represents the line width in pixels of the shape's outline. BaseMethod1 Method A test method which, when invoked, fires the BaseEvent1 event. Takes a single parameter of type long. BaseMethod2 Method A test method which, when invoked, fires the BaseEvent2 event. Takes a single parameter of type BSTR. BaseEvent1 Event A test event. Returns a long. BaseEvent2 Event A test event. Returns a BSTR. The CCircleCtrl class provides the functionality of a simple circle control. It implements the following properties, events, and methods: Name Type Use ------------- --------- --------------------------------------------------- CircleShape Property A boolean value. If TRUE the control draws itself as a circle, if FALSE it draws itself as an ellipse. CircleOffset Property A short value which represents the number of pixels offset from the center of the bounding rectangle at which the control will draw itself. CircleMethod1 Method A test method which, when invoked, fires the CircleEvent1 event. Takes a single parameter of type long. CircleMethod2 Method A test method which, when invoked, fires the CircleEvent2 event. Takes a single parameter of type long. CircleEvent1 Event A test event. Returns a long. CircleEvent2 Event A test event. Returns a long. The CRectangleCtrl class provides the functionality of a simple rectangle control. It implements the following properties, events, and methods: Name Type Use -------------- --------- --------------------------------------------------- RoundedCorners Property A boolean value. If TRUE the control draws itself with rounded corners, if FALSE it draws itself with square corners. RectangleInset Property A short value which represents the number of pixels inside the control's bounding rectangle by which the control will inset itself. RectMethod1 Method A test method which, when invoked, fires the RectEvent1 event. Takes no parameters. RectMethod2 Method A test method which, when invoked, fires the RectEvent2 event. Takes no parameters. RectEvent1 Event A test event. Returns void. RectEvent2 Event A test event. Returns void. Modifying the Base Control Class -------------------------------- Several changes need be made to the code generated by ControlWizard to allow a derived control to cleanly inherit the functionality provided by a base control. The following changes were made to the files generated by ClassWizard: 1. The ON_OLEVERB entry for AFX_IDS_VERB_PROPERTIES in the CBaseShapeCtrl message map was removed: BEGIN_MESSAGE_MAP(CBaseShapeCtrl, COleControl) //{{AFX_MSG_MAP(CBaseShapeCtrl) //}}AFX_MSG_MAP //ON_OLEVERB(AFX_IDS_VERB_PROPERTIES, OnProperties) END_MESSAGE_MAP() If this isn't done, control containers will list the Properties... verb twice when the Edit | Control Object menu is selected. 2. The CBaseShapeCtrl::CBaseShapeCtrlFactory::UpdateRegistry function was changed to simply return TRUE: BOOL CBaseShapeCtrl::CBaseShapeCtrlFactory::UpdateRegistry(BOOL bRegister) { return TRUE; } If this isn't done the base control will get registered and containers will list it along with the derived controls when the user attempts to insert a new control. 3. The CBaseShapePropPage::CBaseShapePropPageFactory::UpdateRegistry function was changed to simply return TRUE: BOOL CBaseShapePropPage::CBaseShapePropPageFactory::UpdateRegistry( BOOL bRegister) { return TRUE; } If this isn't done the base class control's property page will get registered and will appear in the registry. 4. The call to InitializeIIDs in the base control class' constructor was removed: CBaseShapeCtrl::CBaseShapeCtrl() { //InitializeIIDs(&IID_DBaseShape, &IID_DBaseShapeEvents); // TODO: Initialize your control's instance data here. } If this isn't done there will be a memory leak upon termination when the cached type information for the base class does not get freed. 5. The base control's section of the project's .ODL file was commented out. If this isn't done, some containers, for example, Visual Basic 4.0, will fail to load the control. 6. The CBaseShapeCtrl::DoPropExchange method was modified to not call the COleControl::ExchangeVersion function: void CBaseShapeCtrl::DoPropExchange(CPropExchange* pPX) { // ExchangeVersion(pPX, MAKELONG(_wVerMinor, _wVerMajor)); COleControl::DoPropExchange(pPX); ... } The _Version property is serialized via a call to the ExchangeVersion method in the DoPropExchange method of the derived control. 7. The DoPropExchange method of the derived OLE controls were changed to make a call to CBaseShapeCtrl::DoPropExchange instead of COleControl::DoPropExchange: void CCircleCtrl::DoPropExchange(CPropExchange* pPX) { ExchangeVersion(pPX, MAKELONG(_wVerMinor, _wVerMajor)); CBaseShapeCtrl::DoPropExchange(pPX); ... } Manually Updating the Project's ODL File ---------------------------------------- ClassWizard does not provide any support for developing OLE controls which are derived from another control. As a result, the property, method, and event dispatch ID's used by a derived control class need to be manually updated. MFC Technical Note #39 discusses the dispatch ID numbering scheme used by MFC. Basically, MFC divides a 32-bit dispatch ID (DISPID) into two parts. The LOWORD of the DISPID contains the distance from the top of the dispatch map (1 relative). The HIWORD contains the distance of the dispatch map from the most derived class (0 relative). The CCircleCtrl and CRectangleControl classes use this technique with their DISPIDs. For example, the CCircleCtrl derived control inherits the FillColor,LineColor, and LineWidth properties from CBaseShapeCtrl. The DISPID's for these properties need to be manually added to the CCircleCtrl properties section of the project's .ODL file and the HIWORD of the DISPID's needs to be adjusted: // Primary dispatch interface for CCircleCtrl [ uuid(A7EC6760-BFED-11CE-8250-524153480001), helpstring("Dispatch interface for sample Circle Control"), hidden ] dispinterface _DCircle { properties: // NOTE - ClassWizard will maintain property information here. // Use extreme caution when editing this section. //{{AFX_ODL_PROP(CCircleCtrl) [id(65537)] OLE_COLOR FillColor; [id(65538)] OLE_COLOR LineColor; [id(65539)] short LineWidth; [id(1)] boolean CircleShape; [id(2)] short CircleOffset; //}}AFX_ODL_PROP ... The FillColor, LineColor, and LineWidth properties implemented in the base class have DISPID's of 1, 2, and 3 respectively. Once the HIWORD portion of these DISPID's has been adjusted they become 65537, 65538, and 65539. The DISPID's for events are handled differently than for properties and methods. Event DISPID's do not have their HIWORD portion adjusted. Instead, they are sequential. For example, CCircleCtrl inherits the BaseEvent1 and BaseEvent2 events from the base control. The DISPID's for the base events need to be manually added to the CCircleCtrl events section of the project's .ODL file. Also, the DISPID's assigned by ClassWizard for the events provided by CCircleCtrl (CircleEvent1 and CircleEvent2) need to have their DISPIDs manually updated: [ uuid(A7EC6761-BFED-11CE-8250-524153480001), helpstring("Event interface for sample Circle Control") ] dispinterface _DCircleEvents { properties: // Event interface has no properties methods: // NOTE - ClassWizard will maintain event information here. // Use extreme caution when editing this section. //{{AFX_ODL_EVENT(CCircleCtrl) [id(1)] void BaseEvent1(long lParam); [id(2)] void BaseEvent2(BSTR pszString); [id(3)] void CircleEvent1(long lParam); [id(4)] void CircleEvent2(long lParam); //}}AFX_ODL_EVENT }; Manually updating the DISPIDs can be problematic because ClassWizard may get confused when it sees the entries for the events in the base class. It's possible that more than one event may be assigned the same DISPID. After adding new events to a derived class, inspect the project's .ODL file and fix any conflicts. ClassWizard also maintains DISPID values for properties, methods, and events, in an enum member of the COleControl derived class. Again, because ClassWizard does not support deriving an OLE control from another control, it may generate conflicting values for the different DISPIDs. If this happens, manually edit the values so that they are correct and match the values as specified in the .ODL file. Following is the portion of the CCircleCtrl class that shows the DISPIDs used for both the base class and derived class properties, events, and methods: class CCircleCtrl : public CBaseShapeCtrl { ... // Dispatch and event IDs public: enum { //{{AFX_DISP_ID(CCircleCtrl) //dispidFillColor = 65537L, //dispidLineColor = 65538L, //dispidLineWidth = 65539L, //dispidBaseMethod1 = 65540L, //dispidBaseMethod2 = 65541L, dispidCircleShape = 1L, dispidCircleOffset = 2L, dispidCircleMethod1 = 3L, dispidCircleMethod2 = 4L, //eventidBaseEvent1 = 1L, //eventidBaseEvent2 = 2L, eventidCircleEvent1 = 3L, eventidCircleEvent2 = 4L, //}}AFX_DISP_ID }; SHAPES is based on a ControlWizard generated OLE control. Files included with the sample which are directly related to deriving an OLE control from a base control are: - SHAPES.ODL: Shows the modified DISPIDs used by the derived control classes. - BASECTL.CPP: Provides the implementation of the base CBaseShapeCtrl class. - CIRCCTL.CPP: Provides the implementation of the derived CCircleCtrl class. - RECTCTL.CPP: Provides the implementation of the derived CRectangleCtrl class. REFERENCES ========== MFC Technical Note #39 Additional query words: Shapes Shapes2 ====================================================================== Keywords : kbcode kbfile kbsample kbActiveX kbCOMt kbCtrlCreate kbMFC kbVC400 kbGrpDSMFCATL kbArchitecture Technology : kbAudDeveloper kbMFC Version : :4.0 Issue type : kbinfo ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.