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Introduction to wxWidgets

, 25 Dec 2005 GPL3
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A beginner's tutorial on wxWidgets for cross platform GUI development.

Introduction

wxWidgets formerly known as wxWindows is a framework for developing cross-platform GUI applications in C++. Julian Smart started the framework in 1992 at the Artificial Intelligence Applications Institute, University of Edinburgh. In 1995, a port to Xt was released by Markus Holzem. In May 1997, the Windows and the GTK+ ports were merged and put into a CVS repository.

What is wxWidgets

wxWidgets gives you a single, easy-to-use API for writing GUI applications on multiple platforms. Link it with the appropriate library for your platform (Windows/Unix/Mac) and compiler (almost any popular C++ compiler), and your application will adopt the look and feel appropriate to that platform. On top of the great GUI functionality, wxWindows gives you: online help, network programming, streams, clipboard and drag and drop, multithreading, image loading and saving in a variety of popular formats, database support, HTML viewing and printing, and much more.

Who should use wxWidgets

wxWidgets is a framework very much similar to MFC, except for a few negative points of its own. Those MFC programmers who are aware of the growing number of Linux users and who want to write cross platform GUI applications can use wxWidgets. With wxWidgets, it is very easy to use a framework based on C++ and it has a proven record of 13 years. In fact, wxWidgets is very stable and is supported on:

  • Windows 3.1, Windows 95/98, Windows NT, Windows 2000/XP, Windows ME, Windows CE.
  • Linux and other UNIX platforms with GTK+.
  • UNIX with Motif or the free Motif clone Lesstif.
  • Mac OS.
  • Embedded platforms are being investigated. See the wxUniversal project.
  • An OS/2 port is in progress, and you can also compile wxWidgets for GTK+ or Motif on OS/2.

Why use wxWidgets

There are a number of options available for writing cross platform GUI development, like: JAVA, Mono.NET, Qt, etc. Java has failed to prove itself as an efficient alternative. Qt is good but commercial and nobody knows its future. Mono.NET seems to be good but is largely driven by Microsoft, it seems like a copy of the work done by Microsoft and it has not yet proved itself as a successful alternative. Also, people would not like to use an extra burden of layer for highly efficient software. As wxWidgets does not use any middle layer and uses only the native controls available on the platform, it gives a nice look and feel to the application.

  • It is very complete. There are many utility classes like : wxRegEx, wxFTP, wxSplashScreen, wxZipInputStream, etc.
  • It is still heavily developed, and has a lot of support from the open source community.
  • Many compilers and platforms are supported : Windows, Linux, Mac, Unix.
  • There's a lot of documentation available on the internet, forums, wxBook.
  • It's free for personal and commercial use, and is more flexible than the LGPL license.
  • Whenever possible, wxWindows uses the platform SDK. This means that a program compiled on Windows will have the look and feel of a Windows program, and when compiled on a Linux machine, it will have the look and feel of a Linux program.
  • Ease of learning, it has the same Event tables and similar API and classes like that of WINAPI and MFC.
  • A lot of sample is provided in the samples directory of the installation, which contains how to use the basic controls, multi threading, MDI, drag and drop, sockets, printing and lots more.
  • A lot of ready to use classes are available, like: wxGenericDirCtrl, wxCalendarCtrl, wxDatePickerCtrl, wxTipWindow, wxStyledTextCtrl, wxStaticPicture, wxLEDNumberCtrl, wxEditableListBox, wxFoldPanelBar, wxGIFAnimationCtrl, wxSplashScreen, OGL (Object Graphics Library), FL (Frame Layout), etc. This is one of the main repository.
  • A lot of add on libraries are available to make the programming task more easier:

Main features

  • Multi threading.
  • Clipboard and drag and drop.
  • Network programming, like: wxSMTP, wxHTTP, wxFTP.
  • Image loading and saving in a variety of popular formats.
  • Streams (ZIP, Network, File, etc.), like: wxRarInputStream.
  • Database support, like: wxDao.
  • HTML viewing and printing, like: wxMozilla, wxIE.
  • XML based resource, multi language/Unicode support.
  • Default style themes available with the OS (e.g.: XP style themes).

Similarity to MFC

MFC and wxWidgets macros

MFC version wxWidgets version
BEGIN_MESSAGE_MAP BEGIN_EVENT_TABLE
END_MESSAGE_MAP END_EVENT_TABLE
DECLARE_DYNAMIC DECLARE_CLASS
DECLARE_DYNCREATE DECLARE_DYMAMIC_CLASS
IMPLEMENT_DYNAMIC IMPLEMENT_CLASS
IMPLEMENT_DYNCREATE IMPLEMENT_DYNAMIC_CLASS
IsKindOf(RUNTIME_CLASS(CWindow)) IsKindOf(CLASSINFO(wxWindow))

MFC and wxWidgets classes

Miscellaneous Classes
MFC version wxWidgets version
CWinApp wxApp
CObject wxObject
CCmdTarget wxEvtHandler
CCommandLineInfo wxCmdLineParser
CMenu wxMenu, wMenuBar, wxMenuItem
CWaitCursor wxBusyCursor
CDataExchange wxValidator
Window Classes
MFC version wxWidgets version
CFrameWnd wxFrame
CMDIFrameWnd wxMDIParentFrame
CMDIChildWnd wxMDIChildFrame
CSplitterWnd wxSplitterWindow
CToolBar wxToolBar
CStatusBar wxStatusBar
CReBar wxCoolBar, but see contrib/src/fl and wxAUI, wxDockIt
CPropertyPage wxPanel
CPropertySheet wxNotebook, wxPropertySheetDialog
Dialog Classes
MFC version wxWidgets version
CDialog wxDialog
CColorDialog wxColourDialog
CFileDialog wxFileDialog
CFindReplaceDialog wxFindReplaceDialog
CFontDialog wxFontDialog
CPageSetupDialog wxPageSetupDialog
CPrintDialog wxPrintDialog
Control Classes
MFC version wxWidgets version
CAnimateCtrl wxMediaCtrl, wxAnimationCtrl
CButton wxButton
CBitmapButton wxBitmapButton
CComboBox wxComboBox, wxChoice
CDateTimeCtrl wxDatePickerCtrl
CEdit wxTextCtrl
CHotKeyCtrl None, but see Keybinder
CListBox, CDragListBox wxListBox
CCheckListBox wxCheckListBox
CListCtrl wxListCtrl, wxListView
CMonthCalCtrl wxCalendarCtrl
CProgressCtrl wxGauge
CReBarCtrl None, but see contrib/src/fl and wxAUI, wxDockIt
CRichEditCtrl wxTextCtrl
CScrollBar wxScrollBar
CSliderCtrl wxSlider
CSpinButtonCtrl wxSpinButton, wxSpinCtrl
CStatic wxStaticText, wxStaticLine, wxStaticBox, wxStaticBitmap
CStatusBarCtrl wxStatusBar
CTabCtrl wxTabCtrl
CToolBarCtrl wxToolBar
CToolTipCtrl wxToolTip
CTreeCtrl wxTreeCtrl
Graphics Classes
MFC version wxWidgets version
CBitmap wxBitmap, wxImage, wxIcon, wxCursor
CBrush wxBrush
CPen wxPen
CFont wxFont
CImageList wxImageList, wxIconBundle
CPalette wxPalette
CRgn wxRegion
CClientDC wxClientDC
CMetaFileDC wxMetaFileDC
CPaintDC wxPaintDC
CWindowDC wxWindowDC
CDC wxDC, wxMemoryDC
Data Structure Classes
MFC version wxWidgets version
CArray, CObArray, CPtrArray wxArray
CStringArray wxArrayString
CDWordArray, CByteArray, CUIntArray wxArrayInt
CList, CPtrList, CObList wxList
CStringList wxArrayString, wxStringList
CMap wxHashMap
CString wxString
CPoint wxPoint
CRect wxRect
CSize wxSize
CTime wxDateTime
CTimeSpan wxTimeSpan, wxDateSpan
COleVariant wxVariant
Internet Classes
MFC version wxWidgets version
CSocket wxSocket
CFtpConnection wxFTP
CHttpConnection wxHTTP
Document/View Classes
MFC version wxWidgets version
CDocument wxDocument
CView wxView
CDocTemplate, CSingleDocTemplate, CMultiDocTemplate wxDocTemplate
Drag and Drop Classes
MFC version wxWidgets version
COleDataSource wxDataObject
COleDropSource wxDropSource
COleDropTarget wxDropTarget
File Classes
MFC version wxWidgets version
CFile wxFile, wxFFile, wxTextFile
CMemFile wxMemoryInputStream, wxMemoryOutputStream
CSocketFile wxSocketInputStream, wxSocketOutputStream
CRecentFileList wxFileHistory
Multithreading Classes
MFC version wxWidgets version
CWinThread wxThread
CCriticalSection wxCriticalSection
CMutex wxMutex
CSemaphore wxSemaphore

Class hierarchy

Getting started

Starting with wxWidgets is really very easy. Just follow these steps:

  • Download the wxMSW-2.6.2-Setup.exe from the sourceforge.net website.
  • Run the setup's EXE and install it in say "C:\wxWidgets\" folder.
  • Add an environment variable $(WXWIN) to your system. The value will be the path of the folder where you have installed wxWidgets.
    1. Right click on the My Computer icon on your desktop.
    2. Select Properties.
    3. A dialog appears. Select the "Advanced" tab in that dialog.
    4. Click "Environment Variables" button.
    5. Another dialog appears. Click on the "New" button in the "System variables" box.
    6. Add "WXWIN" in the "Variable name" text box and the folder path where you have installed wxWidgets in the "Variable value" text box.
    7. Click the OK button till all the dialogs disappear.

  • Open "src\wxWindows.dsw" and "build\msw\wx.dsw" files in Visual studio and build the projects (libraries) in the solution for all the project configurations namely: Debug, Release, Debug DLL, Release DLL, Unicode Debug, Unicode Release, Unicode Debug DLL, Unicode Release DLL. These solution files are in the wxWidgets installation folder. This step will create some libraries needed by our application for linking. These files will be created in the "lib", "lib\vc_lib\" and "lib\vc_dll\" folders under your wxWidgets installation directory.
  • Now everything is ready to feel the power of wxWidgets.

Hello world

Hello world is a classic example to start learning any new language. It gives an overview of the language without going deeper into it.

  • Just create a new project "HelloWorld" in your Visual Studio editor of "Win32 Project" type:

  • In the Application Settings, choose the application type as "Windows Application" and in the Additional options check the "Empty project" checkbox and click the "Finish" button:

  • Now create a new file, by pressing "Ctrl+N", and select the type as "C++ File" in the "Visual C++" categories. Click Open:

  • Now type the following code into the file:
    /*
     * hworld.cpp
     * Hello world sample by Robert Roebling
     */
     
    #include "wx/wx.h" 
     
    
    class MyApp: public wxApp
    {
        virtual bool OnInit();
    };
    
     
    class MyFrame: public wxFrame
    {
    public:
     
        MyFrame(const wxString& title, 
               const wxPoint& pos, const wxSize& size);
    
        void OnQuit(wxCommandEvent& event);
        void OnAbout(wxCommandEvent& event);
     
        DECLARE_EVENT_TABLE()
    };
    
    enum
    {
        ID_Quit = 1,
        ID_About,
    
    };
     
    BEGIN_EVENT_TABLE(MyFrame, wxFrame)
        EVT_MENU(ID_Quit, MyFrame::OnQuit)
        EVT_MENU(ID_About, MyFrame::OnAbout)
    END_EVENT_TABLE()
     
    IMPLEMENT_APP(MyApp)
    
    bool MyApp::OnInit()
    {
        MyFrame *frame = new MyFrame( "Hello World", 
             wxPoint(50,50), wxSize(450,340) );
        frame->Show(TRUE);
        SetTopWindow(frame);
        return TRUE;
    } 
     
    MyFrame::MyFrame(const wxString& title, 
           const wxPoint& pos, const wxSize& size)
    : wxFrame((wxFrame *)NULL, -1, title, pos, size)
    {
        wxMenu *menuFile = new wxMenu;
        menuFile->Append( ID_About, "&About..." );
        menuFile->AppendSeparator();
        menuFile->Append( ID_Quit, "E&xit" );
     
        wxMenuBar *menuBar = new wxMenuBar;
        menuBar->Append( menuFile, "&File" );
     
        SetMenuBar( menuBar );
    
        CreateStatusBar();
        SetStatusText( "Welcome to wxWindows!" );
    }
    
     
    void MyFrame::OnQuit(wxCommandEvent& WXUNUSED(event))
    {
        Close(TRUE);
    }
     
    void MyFrame::OnAbout(wxCommandEvent& WXUNUSED(event))
    {
    
        wxMessageBox("This is a wxWindows Hello world sample",
            "About Hello World", wxOK | wxICON_INFORMATION, this);
    }
  • Now save the file in the same project folder of "HelloWorld" as "Hello.cpp":

  • Now add the file to the project by right clicking on the "Source Files" >> "Add" >> "Add Existing Item…" in the Solution Explorer:

  • Select "Open":

  • Now, select the properties from the project menu:

  • Expand the "C/C++" node and select "General". In the "Additional Include Directories" add the following line for the "Debug" configuration:
    "$(WXWIN)\include";"$(WXWIN)\contrib\include";"$(WXWIN)\lib\mswd"

    And for the "Release" configuration add the following line:

    "$(WXWIN)\include";"$(WXWIN)\contrib\include";"$(WXWIN)\lib\msw"

  • In the Preprocessor tab, add the following line in the "Preprocessor Definitions" for the "Debug" configuration:
    WIN32;_DEBUG;_WINDOWS;__WINDOWS__;__WXMSW__;__WXDEBUG__;WXDEBUG=1;
    __WIN95__;__WIN32__;WINVER=0x0400;STRICT

    And for the "Release" configuration, add the following line:

    NDEBUG,WIN32,_WINDOWS,__WINDOWS__,__WXMSW__,__WIN95__,__WIN32__, 
    WINVER=0x0400,STRICT

  • In the "Code Generation" select the "Runtime Library" for "Debug" configuration as:
    Multi-threaded Debug DLL (/MDd)

    And for the "Releasse" configuration as:

    Multi-threaded DLL (/MD)

  • Expand the "Linker" node and select "General". In the "Additional Library Directories", add the following line for "Debug" configuration:
    "$(WXWIN)\lib";"$(WXWIN)\contrib\lib";"$(WXWIN)\lib\vc_lib"

    And for the "Release" configuration, add the following line:

    "$(WXWIN)\lib";"$(WXWIN)\contrib\lib";"$(WXWIN)\lib\vc_lib"

  • In the "Input" tab add the following line in the "Additional Dependencies" for the "Debug" configuration:
    wxmsw26d_core.lib wxbase26d.lib wxtiffd.lib wxjpegd.lib 
    wxpngd.lib wxzlibd.lib wxregexd.lib wxexpatd.lib
    winmm.lib comctl32.lib rpcrt4.lib wsock32.lib oleacc.lib 
    kernel32.lib user32.lib gdi32.lib winspool.lib
    comdlg32.lib advapi32.lib shell32.lib ole32.lib 
    oleaut32.lib uuid.lib odbc32.lib odbccp32.lib
  • And for the "Release" configuration, add the following line:
    wxmsw26_core.lib wxbase26.lib wxtiff.lib wxjpeg.lib 
    wxpng.lib wxzlib.lib wxregex.lib wxexpat.lib 
    winmm.lib comctl32.lib rpcrt4.lib wsock32.lib oleacc.lib 
    odbc32.lib kernel32.lib user32.lib gdi32.lib
    winspool.lib comdlg32.lib advapi32.lib shell32.lib 
    ole32.lib oleaut32.lib uuid.lib odbccp32.lib

  • Press the "OK" button to save these changes and build the solution from the build menu:

  • Select the "Start" or "Start Without Debugging" from the "Debug" menu to execute the program:

Congratulations!

You have successfully created your first "Hello World" program with wxWidgets:

Visual C++ 2005 Express

Install the Visual C++ 2005 Express by following the instructions given in Manual Installation Instructions for Express Editions and then configure the platform SDK by following steps given in Using Visual C++ 2005 Express Beta 2 with the Microsoft Platform SDK. After this, you need to change the following:

[Editor comment: Line breaks used to avoid scrolling.]

%program Files%\Microsoft Visual Studio 8\VC\VCProjectDefaults\
                                         corewin_express.vsprops

to set "_CRT_SECURE_NO_DEPRECATE;_CRT_NONSTDC_NO_DEPRECATE" as PreprocessorDefinitions.

An example corewin_express.vsprops file:

<?xml version="1.0" ?>
<VisualStudioPropertySheet ProjectType="Visual C++" 
   Version="8.00" Name="Core Windows Libraries">
    <Tool Name="VCLinkerTool" AdditionalDependencies=
        "kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib
        advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib" />
    <Tool Name="VCCLCompilerTool" PreprocessorDefinitions=
        "_CRT_SECURE_NO_DEPRECATE;_CRT_NONSTDC_NO_DEPRECATE" />
</VisualStudioPropertySheet>

Then open the file $(WXWIN)\src\msw\main.cpp, search for the function 'DllMain' and add the following lines:

#if _MSC_VER >= 1400 && _WINDLL
#undef _WINDLL
#endif

before the line:

#if defined(_WINDLL)

After you have configured your Visual Studio, the remaining steps are the same, simply follow the instructions given above for Visual Studio .NET, and open the wx.dsw file and compile the libraries for all the project configurations namely: Debug, Release, Debug DLL, Release DLL, Unicode Debug, Unicode Release, Unicode Debug DLL, Unicode Release DLL.

VC8 has also changed the way manifests are embedded in your executable. Your project will not be built if you include wx.manifest in your resource file. First, exclude the manifest from your resources by adding the define statement to your YourAppName.rc file:

#define wxUSE_NO_MANIFEST 1

Second, add these lines to your one of your source or header files to enable XP-Style common controls:

#if defined(__WXMSW__) && !defined(__WXWINCE__)
#pragma comment(linker, "\"/manifestdependency:type='win32' 
    name='Microsoft.Windows.Common-Controls' version='6.0.0.0'
    processorArchitecture='X86' publicKeyToken='6595b64144ccf1df'\"")
#endif

Linux

Due to the large number of pictures and high downloading time, this section has been moved to a new article. Working with wxWidgets on Linux, can be found here.

Understanding the program

You have to include wxWidgets' header files, of course. This can be done on a file by file basis (such as #include "wx/window.h") or using one global include (#include "wx/wx.h"). This is also useful on platforms that support precompiled headers such as all major compilers on the Windows platform:

// file name: hworld.cpp
//
// purpose: wxWidgets "Hello world"
//

// For compilers that support precompilation,
// includes "wx/wx.h".
#include "wx/wxprec.h"

#ifdef __BORLANDC__
  #pragma hdrstop
#endif

#ifndef WX_PRECOMP
 #include "wx/wx.h"
#endif

Practically, every app should define a new class derived from wxApp. By overriding wxApp's OnInit(), the program can be initialized, e.g. by creating a new main window.

class MyApp: public wxApp { virtual bool OnInit(); };

The main window is created by deriving a class from wxFrame and giving it a menu and a status bar in its constructor. Also, any class that wishes to respond to any "event" (such as mouse clicks or messages from the menu or a button) must declare an event table using the macro below. Finally, a way to react to such events must be done in "handlers". In our sample, we react to two menu items, one for "Quit" and one for displaying an "About" window. These handlers should not be virtual:

class MyFrame: public wxFrame
{
public:
  MyFrame(const wxString& title, const wxPoint& pos, 
                                  const wxSize& size);

  void OnQuit(wxCommandEvent& event);
  void OnAbout(wxCommandEvent& event);

private:
  DECLARE_EVENT_TABLE()
};

In order to be able to react to a menu command, it must be given a unique identifier such as a const or an enum.

enum
{
  ID_Quit = 1,
  ID_About,
};

We then proceed to actually implement an event table in which the events are routed to their respective handler functions in the class MyFrame. There are predefined macros for routing all the common events, ranging from the selection of a list box entry to a resize event when a user resizes a window on the screen. If -1 is given as the ID, the given handler will be invoked for any event of the specified type, so that you could just add one entry in the event table for all menu commands or all button commands etc. The origin of the event can still be distinguished in the event handler as the (only) parameter in an event handler is a reference to a wxEvent object, which holds information about the event (such as the ID of and a pointer to the class, which caused the event).

BEGIN_EVENT_TABLE(MyFrame, wxFrame)
  EVT_MENU(ID_Quit, MyFrame::OnQuit)
  EVT_MENU(ID_About, MyFrame::OnAbout)
END_EVENT_TABLE()

As in all programs, there must be a "main" function. Under wxWidgets, main is implemented using this macro, which creates an application instance and starts the program:

IMPLEMENT_APP(MyApp)

As mentioned above, wxApp::OnInit() is called upon startup and should be used to initialize the program, maybe for showing a "splash screen" and creating the main window (or several). The frame should get a title bar text ("Hello World") and a position and start-up size. One frame can also be declared as the top window. Returning TRUE indicates a successful initialization:

bool MyApp::OnInit()
{
  MyFrame *frame = new MyFrame( "Hello World", 
                    wxPoint(50,50), wxSize(450,340) );
  frame->Show( TRUE );
  SetTopWindow( frame );
  return TRUE;
}

In the constructor of the main window (or later on) we create a menu with two menu items as well as a status bar to be shown at the bottom of the main window. Both have to be "announced" to the frame with the respective calls:

MyFrame::MyFrame(const wxString& title, 
          const wxPoint& pos, const wxSize& size)
 : wxFrame((wxFrame *)NULL, -1, title, pos, size)
{
  wxMenu *menuFile = new wxMenu;

  menuFile->Append( ID_About, "&About..." );
  menuFile->AppendSeparator();
  menuFile->Append( ID_Quit, "E&xit" );

  wxMenuBar *menuBar = new wxMenuBar;
  menuBar->Append( menuFile, "&File" );

  SetMenuBar( menuBar );

  CreateStatusBar();
  SetStatusText( "Welcome to wxWidgets!" );
}

Here are the actual event handlers. MyFrame::OnQuit() closes the main window by calling Close(). The parameter TRUE indicates that other Windows have no veto power, such as after asking "Do you really want to close?". If there is no other main window left, the application will quit:

void MyFrame::OnQuit(wxCommandEvent& WXUNUSED(event))
{
  Close( TRUE );
}

MyFrame::OnAbout() will display a small window i.e. a Message box with some text in it. In this case, a typical "About" window with information about the program:

void MyFrame::OnAbout(wxCommandEvent& WXUNUSED(event))
{
  wxMessageBox( "This is a wxWidgets's Hello world sample", 
    "About Hello World", wxOK | wxICON_INFORMATION );
}

How events are processed

An event table is placed in an implementation file to tell wxWindows how to map events to member functions. These member functions are not virtual functions, but they are all similar in form: they take a single wxEvent-derived argument, and have a void return type.

Here's an example of an event table:

BEGIN_EVENT_TABLE(MyFrame, wxFrame)
  EVT_MENU    (wxID_EXIT, MyFrame::OnExit)
  EVT_MENU    (DO_TEST,   MyFrame::DoTest)
  EVT_SIZE    (           MyFrame::OnSize)
  EVT_BUTTON  (BUTTON1,   MyFrame::OnButton1)
END_EVENT_TABLE()

The first two entries map menu commands to two different member functions. The EVT_SIZE macro doesn't need a window identifier, since normally you are only interested in the current window's size events. (In fact, you could intercept a particular window's size event by using EVT_CUSTOM(wxEVT_SIZE, ID, func).)

The EVT_BUTTON macro demonstrates that the originating event need not come from the window class implementing the event table - if the event source is a button within a panel within a frame, this will still work, because event tables are searched up through the hierarchy of Windows. In this case, the button's event table will be searched, then the parent panel's, and then the frame's.

As mentioned before, the member functions that handle events don't have to be virtual. Indeed, the member functions should not be virtual as the event handler ignores that the functions are virtual, i.e. overriding a virtual member function in a derived class will not have any effect. These member functions take an event argument, and the class of the event differs according to the type of the event and the class of the originating window. For the size events, wxSizeEvent is used. For menu commands and most control commands (such as button presses), wxCommandEvent is used. When controls get more complicated, then specific event classes are used, such as wxTreeEvent for events from wxTreeCtrl windows.

The event table in the implementation file must have a DECLARE_EVENT_TABLE macro in the class definition. For example:

class MyFrame: public wxFrame {

  DECLARE_DYNAMIC_CLASS(MyFrame)

public:
  ...
  void OnExit(wxCommandEvent& event);
  void OnSize(wxSizeEvent& event);
protected:
  int       m_count;
  ...
  DECLARE_EVENT_TABLE()
};

When an event is received from the windowing system, wxWindows calls wxEvtHandler::ProcessEvent on the first event handler object belonging to the window generating the event.

It may be noted that wxWindows' event processing system implements something very close to the virtual methods in normal C++, i.e. it is possible to alter the behavior of a class by overriding its event handling functions. In many cases, this works even for changing the behavior of native controls. For example, it is possible to filter out a number of key events sent by the system to a native text control by overriding wxTextCtrl and defining a handler for key events using EVT_KEY_DOWN. This would indeed prevent any key events from being sent to the native control - which might not be what is desired. In this case, the event handler function has to call Skip() so as to indicate that the search for the event handler should continue.

To summarize, instead of explicitly calling the base class version as you would do with C++ virtual functions (i.e. wxTextCtrl::OnChar()), you should instead call Skip.

In practice, this would look like the following if the derived text control only accepts 'a' to 'z' and 'A' to 'Z':

void MyTextCtrl::OnChar(wxKeyEvent& event)
{
    if ( isalpha( event.KeyCode() ) )
    {
       // key code is within legal range. we call event.Skip() so the
       // event can be processed either in the base wxWindows class
       // or the native control.

       event.Skip();
    }
    else
    {
       // illegal key hit. we don't call event.Skip() so the
       // event is not processed anywhere else.

       wxBell();
    }
}

The normal order of event table searching by ProcessEvent is as follows:

  1. If the object is disabled (via a call to wxEvtHandler::SetEvtHandlerEnabled) the function skips to step (6).
  2. If the object is a wxWindow, the ProcessEvent is recursively called on the window's wxValidator. If this returns TRUE, the function exits.
  3. SearchEventTable is called for this event handler. If this fails, the base class table is tried, and so on, until no more tables exist or an appropriate function is found, in which case the function exits.
  4. The search is applied down the entire chain of event handlers (usually the chain has a length of one). If this succeeds, the function exits.
  5. If the object is a wxWindow and the event is a wxCommandEvent, the ProcessEvent is recursively applied to the parent window's event handler. If this returns TRUE, the function exits.
  6. Finally, ProcessEvent is called on the wxApp object.

Pay close attention to step 5: People often overlook or get confused by this powerful feature of wxWindows event processing system. To put it a different way, events derived either directly or indirectly from wxCommandEvent will travel up the containment hierarchy from child to parent until an event handler is found that doesn't call event.Skip(). Events not derived from wxCommandEvent are sent to the window where they occurred and are then stopped.

Finally, there is another additional complication (which, in fact, simplifies the life of wxWindows programmers significantly): when propagating the command events upwards to the parent window, the event propagation stops when it reaches the parent dialog, if any. This means that you don't risk to get unexpected events from the dialog controls (which might be left unprocessed by the dialog itself because it doesn't care about them) when a modal dialog is popped up. The events do propagate beyond the frames, however. The rationale for this choice is that there are only a few frames in a typical application and their parent-child relation are well understood by the programmer, while it may be very difficult, if not impossible, to track down all the dialogs which may be popped up in a complex program (remember that some are created automatically by wxWindows). If you need to specify a different behavior for some reason, you can use SetExtraStyle(wxWS_EX_BLOCK_EVENTS) explicitly to prevent the events from being propagated beyond the given window or unset this flag for the dialogs which have it by default.

Typically events that deal with a window as a window (size, motion, paint, mouse, keyboard, etc.) are sent only to the window. Events that have a higher level of meaning and/or are generated by the window itself, (button click, menu select, tree expand, etc.) are command events and are sent up to the parent to see if it is interested in the event.

Note that your application may wish to override ProcessEvent to redirect the processing of events. This is done in the document/view framework, for example, to allow event handlers to be defined in the document or view. To test for command events (which are probably the only events you wish to redirect), you may use wxEvent::IsCommandEvent for efficiency, instead of using the slower run-time type system.

As mentioned above, only the command events are recursively applied to the parent's event handler. As this often causes confusion to the users, here is a list of the system events that are not sent to the parent's event handler:

wxEvent The event base class.
wxActivateEvent A window or application activation event.
wxCloseEvent A close window or end session event.
wxEraseEvent An erase background event.
wxFocusEvent A window focus event.
wxKeyEvent A keypress event.
wxIdleEvent An idle event.
wxInitDialogEvent A dialog initialization event.
wxJoystickEvent A joystick event.
wxMenuEvent A menu event.
wxMouseEvent A mouse event.
wxMoveEvent A move event.
wxPaintEvent A paint event.
wxQueryLayoutInfoEvent Used to query layout information.
wxSizeEvent A size event.
wxScrollWinEvent A scroll event sent by a scrolled window (not a scroll bar).
wxSysColourChangedEvent A system color change event.
wxUpdateUIEvent A user interface update event.

In some cases, it might be desired by the programmer to get a certain number of system events in a parent window, for example, all the key events sent to, but not used by, the native controls in a dialog. In this case, a special event handler will have to be written that will override ProcessEvent() in order to pass all the events (or any selection of them) to the parent window.

Additional points

  • You can create a "stdwx.h" file similar to the "stdafx.h" in MFC as a precompiled header. In the project settings in "C/C++" tab in the "Precompiled Headers" select "Automatically Generate (/YX)" for the "Create/Use Precompiled Header" and "stdwx.h" for the "Create/Use PCH Through File". The content of the "stdwx.h" file is as follows:
    #ifndef _stdwx_h_
    #define _stdwx_h_
    
    // SYSTEM INCLUDES
    #include <wx/wxprec.h>
    #ifdef __BORLANDC__
        #pragma hdrstop
    #endif
    #ifndef WX_PRECOMP
        #include "wx/wx.h"
    #endif
    
    // APPLICATION INCLUDES
    #endif
  • Also for the "Additional Include Directories" for the "Resources" tab in "General", for the Debug and Release configuration use:
    "$(WXWIN)\include";
  • The "setup.h" file in the wxWidgets installation has a number of switches. These switches can be used to enable/disable support for functionalities like ODBC, STL, etc. and will compile only those classes that will be used by you. They are simple define statements, whose value can be changed to 1 for enabling and 0 for disabling.

About EyeCare

Eye Care is basically inspired from Alok Gupta's application. It's a small utility program that reminds you, after a preset time interval, to give rest to your eyes and wash them, when you are lost in the matrix of programming. It sits in the taskbar, and monitors your eyes. Completely written in wxWidgets, it's another example of how easy it is to program in wxWidgets. It also shows how to put an application icon in the taskbar, save application configuration, work with images, process window specific messages, use the wxCode components like wxHyperlinkCtrl, and other concepts.

wxVisualIntergration and wxVCExpressIntegration

wxVisualIntergration and wxVCExpressIntegration written by Priyank Bolia, integrates wxWidgets support for Visual Studio .NET 2003 and Visual C++ 2005 Express by providing various wizards. The wxVisualIntergration can be downloaded from here and the wxVCExpressIntegration can be downloaded from here.

Features

  • Provides project wizard for Windows, console and DLL based applications.
  • All types of project settings, like enable Unicode, static/dynamic link, using a few mouse clicks.
  • Additional properties to choose from, like: single instance, WinXP theme, wxFormBuilder support.
  • Saves a lot of precious time, and reduces the error due to manual setting.
  • Projects have debug memory management, pre compiled headers, default menus, toolbar, statusbar, etc.

Useful sites

Some popular applications using wxWidgets

Conclusion

The wxWidgets license is essentially L-GPL (Library General Public Licence), with the exception that the derived works in binary form may be distributed on the user's own terms. This is a solution that satisfies those who wish to produce GPL'ed software using wxWidgets, and also those producing proprietary software. As you have seen, wxWidgets is the fastest to learn, easiest to use and the best possible solution (no royalties, no patents) for Windows programmers in the ever growing world of Linux and MAC.

License

This article, along with any associated source code and files, is licensed under The GNU General Public License (GPLv3)

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About the Author

Priyank Bolia
Software Developer (Senior)
India India
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Comments and Discussions

 
GeneralMissing dsw file in wxWidgets 2.8.7 install PinmemberPaul Runner11-Jun-08 8:57 
GeneralRe: Missing dsw file in wxWidgets 2.8.7 install PinmemberPriyank Bolia11-Jun-08 9:08 
GeneralEnabling wxGLCanvas support for OpenGL on Visual Studio PinmemberPranline3-Jun-08 16:49 
GeneralRe: Enabling wxGLCanvas support for OpenGL on Visual Studio PinmemberPriyank Bolia3-Jun-08 21:44 
QuestionIs there code repository about wxWidgets like codeproject? Pinmemberfantasy121514-May-08 0:03 
AnswerRe: Is there code repository about wxWidgets like codeproject? PinmemberPriyank Bolia14-May-08 0:16 
QuestionRe: Is there code repository about wxWidgets like codeproject? Pinmemberfantasy121515-May-08 17:00 
AnswerRe: Is there code repository about wxWidgets like codeproject? PinmemberPriyank Bolia15-May-08 18:40 
General[Message Deleted] PinmemberMember 45960665-May-08 20:50 
GeneralRe: How can we disable other button ,on pressing button1. PinmemberPriyank Bolia5-May-08 21:11 
GeneralRe: How can we disable other button ,on pressing button1. PinmemberMember 45960665-May-08 21:20 
GeneralWorking with some changes on Windows XP with Visual Studio 2005 and wxWidgets-2.8.7 Pinmemberxiul1-May-08 16:07 
GeneralRe: Working with some changes on Windows XP with Visual Studio 2005 and wxWidgets-2.8.7 [modified] PinmemberPranline10-May-08 11:41 
Hi your post helped me out a lot. I'm still getting errors about the wxString. This is the error I'm getting
 
Error 2 error C2664: 'MyFrame::MyFrame(const wxString &,const wxPoint &,const wxSize &)' : cannot convert parameter 1 from 'const char [12]' to 'const wxString &'
 

I know you told us to took at the site but can you give me a specific example on how your fixed your problem with regards to the Hello World Example?
 
Thanks!
 
modified on Thursday, May 15, 2008 4:05 PM

GeneralRe: Working with some changes on Windows XP with Visual Studio 2005 and wxWidgets-2.8.7 PinmemberPriyank Bolia10-May-08 19:46 
GeneralRe: Working with some changes on Windows XP with Visual Studio 2005 and wxWidgets-2.8.7 PinmemberPranline15-May-08 11:06 
QuestionIs it possible to make a dialog box in frame window ??? PinmemberMember 459606625-Apr-08 4:03 
AnswerRe: Is it possible to make a dialog box in frame window ??? PinmemberPriyank Bolia25-Apr-08 4:50 
QuestionHow to Add Group box that contain some control? PinmemberMember 459606621-Apr-08 0:23 
AnswerRe: How to Add Group box that contain some control? PinmemberPriyank Bolia21-Apr-08 2:53 
QuestionHow to disable maximize button in Window? PinmemberMember 459606618-Apr-08 1:12 
Questionwindow That should be NON stectchable?????? PinmemberMember 459606617-Apr-08 22:40 
AnswerRe: window That should be NON stectchable?????? PinmemberPriyank Bolia17-Apr-08 22:57 
Generalunstrechable window i.e window with fixed size given by user. PinmemberMember 459606617-Apr-08 0:25 
GeneralRe: unstrechable window i.e window with fixed size given by user. PinmemberPriyank Bolia17-Apr-08 3:03 
QuestionCan we add controls like button ,listbox,combobox, etc in upper part of splitter window????? PinmemberMember 459606615-Apr-08 2:40 
AnswerRe: Can we add controls like button ,listbox,combobox, etc in upper part of splitter window????? PinmemberPriyank Bolia15-Apr-08 2:51 
GeneralwxWidgets good introduction tutorial Pinmembervirgil_trasca30-Mar-08 7:58 
GeneralwxArray question PinmemberIlanTal16-Oct-07 6:29 
GeneralRe: wxArray question PinmemberPriyank Bolia16-Oct-07 7:29 
Generalcan't find setup.h PinmemberIlanTal8-Oct-07 4:48 
GeneralRe: can't find setup.h PinmemberPriyank Bolia9-Oct-07 6:47 
GeneralRe: can't find setup.h PinmemberIlanTal10-Oct-07 4:32 
GeneralRe: can't find setup.h PinmemberPriyank Bolia10-Oct-07 5:43 
QuestionEye Care link doesn't work Pinmemberiyhernandezo16-Dec-06 10:55 
AnswerRe: Eye Care link doesn't work PinmemberPriyank Bolia16-Dec-06 20:18 
QuestionwxVCExpressIntegration Pinmemberspidertp29-Oct-06 23:51 
AnswerRe: wxVCExpressIntegration PinmemberPriyank Bolia30-Oct-06 1:36 
GeneralRe: wxVCExpressIntegration Pinmemberspidertp30-Oct-06 2:30 
QuestionRe: wxVCExpressIntegration PinmemberJG3316-May-08 7:27 
AnswerRe: wxVCExpressIntegration PinmemberPriyank Bolia16-May-08 7:35 
GeneralVC++ 2005 with wxWidgets Update PinmemberMike Bluett17-Aug-06 15:50 
GeneralRe: VC++ 2005 with wxWidgets Update PinmemberPriyank Bolia17-Aug-06 18:43 
GeneralRe: VC++ 2005 with wxWidgets Update [modified] PinmemberMike Bluett18-Aug-06 17:29 
GeneralRe: VC++ 2005 with wxWidgets Update PinmemberJosef Meile24-May-07 11:13 
GeneralRe: VC++ 2005 with wxWidgets Update PinmemberJosef Meile24-May-07 11:50 
GeneralRe: VC++ 2005 with wxWidgets Update PinmemberMike Bluett30-May-07 15:50 
GeneralwxWidgets is a joke comparing to Ultimate++ or vcf... Pinmemberarilect12-Aug-06 0:47 
GeneralRe: wxWidgets is a joke comparing to Ultimate++ or vcf... PinmemberPriyank Bolia12-Aug-06 1:09 
GeneralRe: wxWidgets is a joke comparing to Ultimate++ or vcf... Pinmembervortic12-Aug-06 8:42 
GeneralRe: wxWidgets is a joke comparing to Ultimate++ or vcf... Pinmemberluzr14-Aug-06 10:14 

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