Class for Synchronizing the Active State of multiple windows.

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<CMainDlg>
   , public ISyncActiveImpl<CMainDlg>
   , 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<CMainDlg>(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<CFloatingWindow>(TRUE)
     {
     }
   

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

   BEGIN_MSG_MAP(CMainDlg)
     CHAIN_MSG_MAP(ISyncActiveImpl<CMainDlg>)
     .
     .
     .
   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.

History

• 11 mar 2002
  • first public version.

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