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VC++ Mfc Examples - Create Fixed Size Sdi Window Using Precreatewindow Override

Updated on August 18, 2018
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I am a software engineer. I have been working with C++, MFC, and .net technologies for 15 years. I like playing video games & reading books.

Fixed Size MFC SDI Application
Fixed Size MFC SDI Application | Source

1. Introduction To PrecreateWindow

In this article, we will look at eliminating the minimize and maximize button from the MFC Single Document Interface (SDI) Application. Of course, we can achieve that with the MFC Application Wizard itself. However, it is restricted to design time. Moreover, knowing how to do that in run time is effective as the Application can react based on the INI file or Configuration file settings.

Before we continue, First, we will create an SDI Application with maximize and minimize buttons. You can watch the below video which shows creating a skeleton of Visual C++ SDI Application for this Example.

The class CMainFrame class of MFC Framework is responsible for creating and managing Application’s Main Window which houses the Toolbar, Status Bar and Menu, etc. We can change its style by altering the CREATESTRUCT structure while the Application Window is loading. MFC Framework calls the PreCreateWindow function before presenting the Window to the user. One can override this function to modify the CREATESTRUCT which is passed as a reference parameter to it.

2. The CreateStruct

When we created the SDI Application, the wizard created a PrecreateWindow override for us. The default implementation of the function is shown below:

BOOL CMainFrame::PreCreateWindow(CREATESTRUCT& cs)
{
	if( !CFrameWnd::PreCreateWindow(cs) )
		return FALSE;
	// TODO: Modify the Window class 
	//or styles here by modifying
	//  the CREATESTRUCT cs

	return TRUE;
}

The below video shows show to navigate to the PreCreateWindow Function.

Video 2: Navigate to PreCreateWindow Override

In the above code snippet, we can see that MFC Framework supplies CREATESTRUCT as a parameter to the PreCreateWindow override. One can change the style of the SDI Application Window by adjusting CREATESTRUCT structure.

Note that the MFC Framework calls PreCreateWindow function before displaying the Window to the user. Furthermore, the MFC fills the CREATESTRUCT with default options (Or One changed in the Wizard, Refer Video 1) and supplies that to the PreCreateWindow function. Remember, while creating the Application through Wizard we opted for Minimize and Maximize buttons and MFC fills CREATESTRUCT with these informations. As a matter of fact, we have the final chance to override those display styles of the MainFrame Window. Note that MFC passes the CREATESTRUCT as a reference and hence the change we make on it will reflect to the caller. The MFC Framework caller will make use of this changed structure and draws the Mainframe Window.

3. Controlling the CMainFrame Window Style

We are going to set four styles to the CREATESTRUCT. They are:

  1. Set MainFrame window of the SDI application as Fixed Size Window so that user cannot resize it.
  2. Hide the Minimize button from the MainFrame window.
  3. Hide the Maximize button to avoid Maximizing the window.
  4. Hide the default title MFC SDI MainFrame Window.
  5. Set the size of the Window to 500 x 250 Pixels.

The below code will do all the above said adjustments:

BOOL CMainFrame::PreCreateWindow(CREATESTRUCT& cs)
{
	if( !CFrameWnd::PreCreateWindow(cs) )
		return FALSE;

	//Snippet 01: Hide Minimize and Maximize
	cs.style = cs.style & ~WS_MAXIMIZEBOX;
	cs.style = cs.style & ~WS_MINIMIZEBOX;

	//Snippet 02: Make MFC mainframe with fixed size
	cs.style = cs.style & ~WS_THICKFRAME;

	//Snippet 03: Hide Title of the MainFrameWindow
	cs.style = cs.style & ~FWS_ADDTOTITLE;

	//Snippet 04: Resize MainFrameWnd to 500 x 250 Pixels
	cs.cx = 500;
	cs.cy = 250;


	return TRUE;
}

Note, that the CREATESTRUCT is pre-populated with the default settings which is provided by us in the Application Wizard. To remove a particular setting, we are using the “~ Bitwise Operator” so that it will remove it from the style. For Example, ~WS_MINIMIZEBOX will remove the bit for Minimizebox and the Bitwise AND (&) with the CREATESTRUCT cs will remove that style from it. The same way we remove other settings as described below:

  1. WS_MAXIMIZEBOX controls the Maximize button
  2. WS_MINIMIZEBOX controls the Minimize button
  3. WS_THICKFRAME controls the SDI is sizable or not
  4. FWS_ADDTOTITLE controls the display of default title
  5. And Finally, cx and cy are used to set the Width and Height of the MainFrame Window.

The below video shows how the modified code works with MainFrame Window.

Video 3: Fixed Size MainFrame Window

4. Conclusion

Changing window style at run-time is useful when we want adjust the window style on the Fly or to act upon the application settings. In this example, we used CREATESTRUCT to set the SDI Application window size. One can change the size using the Win32 API functions also.

There are other useful window styles like WS_CAPTION, WS_SYSMENU, etc that we can control through the CREATESTRUCT structure. Refer MSDN to know more Window Style Constants.

© 2018 sirama

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