Auto repositioning/resizing of child controls (using C++ templates)

Yet, another method to reposition/resize child windows within their parent framework. Although the subject received a lot of attention, including this web site, I invite you to look at the following method as it presents certain advantages over the others I already know.

First of all this is not a library. There is no associated DLL or LIB to link to. Secondly, it is not a class hierarchy. You dont have to derive your classes from classes exposing this functionality. Often, you already have a hierarchy of classes designed for a certain behavior. This behavior does not include repositioning/resizing of child controls, but you want to add it. Since the MFC doesnt let you use multiple inheritance when it comes to windows, you might wonder what is the solution. Well, the solution is templates. GEOMETRY is actually a collection of templates designed to make your windows to resize gracefully.

The interface to GEOMETRY is a single class template CGeometryWnd. You can use this class template with all your window classes including dialogs, forms, property sheets/property pages and splitter windows. Being a template library, GEOMETRY is contained in a single file Geometry.h. All you have to do is to include this file, to use CGeometryWnd and possibly a series of macros, in relation with your classes.

For example to make a dialog resizeable you need to:

  1. make your dialog in resource editor resizeable (replace the dialog frame with a resizeable border)
  2. specify the rules to apply to child controls (either in the resource editor or in the source code)
  3. include in dialogs source code Geometry.h
  4. use the template CGeometryWnd over your dialogs class


#include Geometry.h
// CAboutDlg dialog used for App About

class CAboutDlg : public CDialog


 // Dialog Data
 enum { IDD = IDD_ABOUTBOX };

 virtual BOOL OnInitDialog();
 virtual void DoDataExchange(CDataExchange* pDX);    // DDX/DDV support

// Implementation
 // No message handlers

CAboutDlg::CAboutDlg() : CDialog(CAboutDlg::IDD)

void CAboutDlg::DoDataExchange(CDataExchange* pDX)

// No message handlers

BOOL CAboutDlg::OnInitDialog()

 return TRUE;

// App command to run the dialog
void CTestPSGeoApp::OnAppAbout()
 CGeometryWnd<CAboutDlg> aboutDlg;
The constraints added to child windows, control their behavior in case the parent resizes. The constraints can be added at design time (aka in resource editor, see note) or at runtime using the DECLARE_GEOMETRY_RTSUPPORT() macro and AddConstraint()function. The constraint object has two important constructors:

CConstraint(LPCSTR lpOptions) and
CConstraint(float x,float y=0,float cx=0,float cy=0)
In the first case you can specify the repositioning/resizing of the control by using a control string (see table for details). Basically the string format is:


Where Optionx (see table below) controls the position/size of the control and [value] ([] are not optional) is an optional parameter specifying the amount (between 0 and 1 as a float number) with which the control will reposition/resize from the total amount of the parent resize value.





Reposition on x axis

Control will move on the x axis


Reposition on y axis

Control will move on the y axis


Resize on x axis

Control will resize its width


Resize on y axis

Control will resize its height


Stay on x axis center

Equivalent with X[0.5]


Stay on y axis center

Equivalent with Y[0.5]



Equivalent with CX[0.5]



Equivalent with CY[0.5]


Maintain aspect on x axis

Preserves the X/CXParent ratio


Maintain aspect on y axis

Preserves the Y/CYParent ratio


Maintain aspect on the width

Preserves the CX/CXParent ratio


Maintain aspect on the height

Preserves the CY/CYParent ratio


To add the constraints at design time directly in resource editor you ll gonna surround the controls sharing the same constraint options with invisible group boxes having the caption in the form " $Geometry:Option1[value]+Option2[value]+" w/o the quotes. Please note the $Geometry in front of the options string, this is not optional. Be careful with the capital/minor letters as they have different significance. Using this form of constraints specification you dont need DECLARE_GEOMETRY_RTSUPPORT() and AddConstraint() as previously displayed.

Using the second constructor you will specify the values between 0 and 1 that will be multiplied with the total resize amount of the parent. A value of 0 means dont move/resize a value of 1 means full movement/resizing. Please note that the values of movement/resizing on one axis added together must not be greater than 1 (otherwise the control will be clipped away from its parent).

AddConstraint(UINT nIDC,CConstraint& constraint) takes as parameters the control ID and a reference to a constraint object.

To achieve dynamic creation of windows MFC uses DECLARE_DYNCREATE(), IMPLEMENT_DYNCREATE() along with RUNTIME_CLASS() macros. For example the CFormView derived classes are usually created by the framework in this way. To accommodate this case GEOMETRY uses a set of macros of its own:


The first macro is to be used in the definition of the class (however outside the class scope), the second in the implementation of the class and eventually the third instead of RUNTIME_CLASS(). The first two dont replace DECLARE_DYNCREATE(), IMPLEMENT_DYNCREATE() macros, they still have to be used.

For example:

#include <Geometry.h>
class CTestPSGeoView : public CFormView
 protected: // create from serialization only

In the definition file of the CTestPSGeoView class and


In the implementation file.

Also, there is necessary the substitution:

CMultiDocTemplate* pDocTemplate;
pDocTemplate = new CMultiDocTemplate(
RUNTIME_CLASS(CChildFrame), // custom MDI child frame

Thats it! An example along with the full source code is provided. You may use freely this template library, even modify it, but at your own risk and specifying where the code comes from. The template library was built and tested on VC 6.0 only.

Download demo project - 36 KB

Date Last Updated: February 4, 1999

This article was originally published on February 4th, 1999

Most Popular Programming Stories

More for Developers

RSS Feeds

Thanks for your registration, follow us on our social networks to keep up-to-date