Class for Synchronizing the Active State of multiple windows.

• Download demo and source code - 30 Kb

   

  
  

  Introduction

  With the class ISyncActiveImpl, of this article, you can have windows that synchronize the active state with a owner window.

  Features implemented:

  
  
  
  
  • Windows that can synchronize the active state with a owner window;
  
  
  • Windows that automatically hide when the application is deactivated and when the owner window is minimized or hidden;
  
  
  • Windows that are automatically disabled when owner window is disabled.
  
  

   

  
  

  Usage

  I will base these examples in the source-code of the demo application included in this article.

  
  
  
  

  1. Include the ISyncActiveImpl.h header file in your source-file.

     
     
  
  

  2. Derive your class from ISyncActiveImpl<>.

      

     class CMainDlg :
     public CDialogImpl
     , public ISyncActiveImpl
     , public CMessageFilter
     

  
  

  3. In your class constructor make sure that you instantiate ISyncActiveImpl<> class with the right arguments for your type of window.

     For example, for creating a dialog or frame window:

      

     CMainDlg()
     // this dialog does not sync the active state with
     // owner and it must be always visible.
     : ISyncActiveImpl(FALSE, TRUE)
     {
     }

     Or for creating a floating or toolbar window:

      

     CFloatingWindow()
     // this window will synchronize the active state with
     // owner and will automatically be hidden when owner
     // is hidden/minimized or when application looses the
     // active state.
     : ISyncActiveImpl(TRUE)
     {
     }
     

  
  

  4. In the message map of your class add a CHAIN_MSG_MAP macro.

      

     BEGIN_MSG_MAP(CMainDlg)
     CHAIN_MSG_MAP(ISyncActiveImpl)
     .
     .
     .
     END_MSG_MAP()

     NOTE: Make sure that you insert it on the first entry of the message map. This is needed because the ISyncActiveImpl<> class will need to intercept some general messages (i.e. WM_CREATE).

     
     
  
  
  
  

  Under the hood

  The key for synchronizing the active state of a window lies on the WM_NCACTIVATE message. By handling or sending this message we can force the painting of a window in the active or inactive state.

  The automatically hide of a window is archived by handling the WM_ACTIVATEAPP message.

  The other two important messages that need to be handled are WM_ACTIVATE and WM_SHOWWINDOW, you can find information about them in source-code and at MSDN.

  For ending, I just want to say that when implementing this class I have run into two "strange" activation problems, read all about them in the source-code.