XML-based resource system overview

XML-based resource system overview

Classes: wxXmlResource, wxXmlResourceHandler

The XML-based resource system, known as XRC, allows user interface elements such as dialogs, menu bars and toolbars, to be stored in text files and loaded into the application at run-time. XRC files can also be compiled into binary XRS files or C++ code (the former makes it possible to store all resources in a single file and the latter is useful when you want to embed the resources into the executable).

There are several advantages to using XRC resources.

Recompiling and linking an application is not necessary if the resources change.
If you use a dialog designer that generates C++ code, it can be hard to reintegrate this into existing C++ code. Separation of resources and code is a more elegant solution.
You can choose between different alternative resource files at run time, if necessary.
The XRC format uses sizers for flexibility, allowing dialogs to be resizable and highly portable.
The XRC format is a wxWidgets standard, and can be generated or postprocessed by any program that understands it. As it is based on the XML standard, existing XML editors can be used for simple editing purposes.

XRC was written by Vaclav Slavik.

XRC concepts
Using binary resource files
Using embedded resources
XRC C++ sample
XRC resource file sample
XRC file format
C++ header file generation
Adding new resource handlers

XRC concepts

These are the typical steps for using XRC files in your application.

Include the appropriate headers: normally "wx/xrc/xmlres.h" will suffice;
If you are going to use XRS files, install wxFileSystem ZIP handler first with wxFileSystem::AddHandler(new wxZipFSHandler);
call wxXmlResource::Get()->InitAllHandlers() from your wxApp::OnInit function, and then call wxXmlResource::Get()->Load("myfile.xrc") to load the resource file;
to create a dialog from a resource, create it using the default constructor, and then load it using for example wxXmlResource::Get()->LoadDialog(&dlg, this, "dlg1");
set up event tables as usual but use the XRCID(str) macro to translate from XRC string names to a suitable integer identifier, for example EVT_MENU(XRCID("quit"), MyFrame::OnQuit).

To create an XRC file, you can use one of the following methods.

Create the file by hand;
use wxDesigner, a commercial dialog designer/RAD tool;
use DialogBlocks, a commercial dialog editor;
use XRCed, a wxPython-based dialog editor that you can find in the wxPython/tools subdirectory of the wxWidgets CVS archive;
use wxGlade, a GUI designer written in wxPython. At the moment it can generate Python, C++ and XRC;
convert WIN32 RC files to XRC with the tool in contrib/utils/convertrc.

A complete list of third-party tools that write to XRC can be found at www.wxwidgets.org/lnk_tool.htm.

It is highly recommended that you use a resource editing tool, since it's fiddly writing XRC files by hand.

You can use wxXmlResource::Load in a number of ways. You can pass an XRC file (XML-based text resource file) or a zip-compressed file (extension ZIP or XRS) containing other XRC.

You can also use embedded C++ resources

Using binary resource files

To compile binary resource files, use the command-line wxrc utility. It takes one or more file parameters (the input XRC files) and the following switches and options:

-h (--help): show a help message
-v (--verbose): show verbose logging information
-c (--cpp-code): write C++ source rather than a XRS file
-e (--extra-cpp-code): if used together with -c, generates C++ header file containing class definitions for the windows defined by the XRC file (see special subsection)
-u (--uncompressed): do not compress XML files (C++ only)
-g (--gettext): output underscore-wrapped strings that poEdit or gettext can scan. Outputs to stdout, or a file if -o is used
-n (--function) <name>: specify C++ function name (use with -c)
-o (--output) <filename>: specify the output file, such as resource.xrs or resource.cpp
-l (--list-of-handlers) <filename>: output a list of necessary handlers to this file

For example:

  % wxrc resource.xrc
  % wxrc resource.xrc -o resource.xrs
  % wxrc resource.xrc -v -c -o resource.cpp

Note

XRS file is essentially a renamed ZIP archive which means that you can manipulate it with standard ZIP tools. Note that if you are using XRS files, you have to initialize the wxFileSystem ZIP handler first! It is a simple thing to do:

  #include <wx/filesys.h>
  #include <wx/fs_zip.h>
  ...
  wxFileSystem::AddHandler(new wxZipFSHandler);

Using embedded resources

It is sometimes useful to embed resources in the executable itself instead of loading an external file (e.g. when your app is small and consists only of one exe file). XRC provides means to convert resources into regular C++ file that can be compiled and included in the executable.

Use the -c switch to wxrc utility to produce C++ file with embedded resources. This file will contain a function called InitXmlResource (unless you override this with a command line switch). Use it to load the resource:

  extern void InitXmlResource(); // defined in generated file
  ...
  wxXmlResource::Get()->InitAllHandlers();
  InitXmlResource();
  ...

XRC C++ sample

This is the C++ source file (xrcdemo.cpp) for the XRC sample.

#include "wx/wx.h"
#include "wx/image.h"
#include "wx/xrc/xmlres.h"

// the application icon
#if defined(__WXGTK__) || defined(__WXMOTIF__) || defined(__WXMAC__)
    #include "rc/appicon.xpm"
#endif

// ----------------------------------------------------------------------------
// private classes
// ----------------------------------------------------------------------------

// Define a new application type, each program should derive a class from wxApp
class MyApp : public wxApp
{
public:
    // override base class virtuals
    // ----------------------------

    // this one is called on application startup and is a good place for the app
    // initialization (doing it here and not in the ctor allows to have an error
    // return: if OnInit() returns false, the application terminates)
    virtual bool OnInit();
};

// Define a new frame type: this is going to be our main frame
class MyFrame : public wxFrame
{
public:
    // ctor(s)
    MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size);

    // event handlers (these functions should _not_ be virtual)
    void OnQuit(wxCommandEvent& event);
    void OnAbout(wxCommandEvent& event);
    void OnDlg1(wxCommandEvent& event);
    void OnDlg2(wxCommandEvent& event);

private:
    // any class wishing to process wxWidgets events must use this macro
    DECLARE_EVENT_TABLE()
};

// ----------------------------------------------------------------------------
// event tables and other macros for wxWidgets
// ----------------------------------------------------------------------------

BEGIN_EVENT_TABLE(MyFrame, wxFrame)
    EVT_MENU(XRCID("menu_quit"),  MyFrame::OnQuit)
    EVT_MENU(XRCID("menu_about"), MyFrame::OnAbout)
    EVT_MENU(XRCID("menu_dlg1"), MyFrame::OnDlg1)
    EVT_MENU(XRCID("menu_dlg2"), MyFrame::OnDlg2)
END_EVENT_TABLE()

IMPLEMENT_APP(MyApp)

// ----------------------------------------------------------------------------
// the application class
// ----------------------------------------------------------------------------

// 'Main program' equivalent: the program execution "starts" here
bool MyApp::OnInit()
{
    wxImage::AddHandler(new wxGIFHandler);
    wxXmlResource::Get()->InitAllHandlers();
    wxXmlResource::Get()->Load("rc/resource.xrc");

    MyFrame *frame = new MyFrame("XML resources demo",
                                 wxPoint(50, 50), wxSize(450, 340));
    frame->Show(true);
    return true;
}

// ----------------------------------------------------------------------------
// main frame
// ----------------------------------------------------------------------------

// frame constructor
MyFrame::MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size)
       : wxFrame((wxFrame *)NULL, -1, title, pos, size)
{
    SetIcon(wxICON(appicon));

    SetMenuBar(wxXmlResource::Get()->LoadMenuBar("mainmenu"));
    SetToolBar(wxXmlResource::Get()->LoadToolBar(this, "toolbar"));
}

// event handlers
void MyFrame::OnQuit(wxCommandEvent& WXUNUSED(event))
{
    // true is to force the frame to close
    Close(true);
}

void MyFrame::OnAbout(wxCommandEvent& WXUNUSED(event))
{
    wxString msg;
    msg.Printf( _T("This is the about dialog of XML resources demo.\n")
                _T("Welcome to %s"), wxVERSION_STRING);

    wxMessageBox(msg, "About XML resources demo", wxOK | wxICON_INFORMATION, this);
}

void MyFrame::OnDlg1(wxCommandEvent& WXUNUSED(event))
{
    wxDialog dlg;
    wxXmlResource::Get()->LoadDialog(&dlg, this, "dlg1");
    dlg.ShowModal();
}

void MyFrame::OnDlg2(wxCommandEvent& WXUNUSED(event))
{
    wxDialog dlg;
    wxXmlResource::Get()->LoadDialog(&dlg, this, "dlg2");
    dlg.ShowModal();
}

XRC resource file sample

This is the XML file (resource.xrc) for the XRC sample.

<?xml version="1.0"?>
<resource version="2.3.0.1">
  <object class="wxMenuBar" name="mainmenu">
    <style>wxMB_DOCKABLE</style>
    <object class="wxMenu" name="menu_file">
      <label>_File</label>
      <style>wxMENU_TEAROFF</style>
      <object class="wxMenuItem" name="menu_about">
        <label>_About...</label>
        <bitmap>filesave.gif</bitmap>
      </object>
      <object class="separator"/>
      <object class="wxMenuItem" name="menu_dlg1">
        <label>Dialog 1</label>
      </object>
      <object class="wxMenuItem" name="menu_dlg2">
        <label>Dialog 2</label>
      </object>
      <object class="separator"/>
      <object class="wxMenuItem" name="menu_quit">
        <label>E_xit\tAlt-X</label>
      </object>
    </object>
  </object>
  <object class="wxToolBar" name="toolbar">
    <style>wxTB_FLAT|wxTB_DOCKABLE</style>
    <margins>2,2</margins>
    <object class="tool" name="menu_open">
      <bitmap>fileopen.gif</bitmap>
      <tooltip>Open catalog</tooltip>
    </object>
    <object class="tool" name="menu_save">
      <bitmap>filesave.gif</bitmap>
      <tooltip>Save catalog</tooltip>
    </object>
    <object class="tool" name="menu_update">
      <bitmap>update.gif</bitmap>
      <tooltip>Update catalog - synchronize it with sources</tooltip>
    </object>
    <separator/>
    <object class="tool" name="menu_quotes">
      <bitmap>quotes.gif</bitmap>
      <toggle>1</toggle>
      <tooltip>Display quotes around the string?</tooltip>
    </object>
    <object class="separator"/>
    <object class="tool" name="menu_fuzzy">
      <bitmap>fuzzy.gif</bitmap>
      <tooltip>Toggled if selected string is fuzzy translation</tooltip>
      <toggle>1</toggle>
    </object>
  </object>
  <object class="wxDialog" name="dlg1">
    <object class="wxBoxSizer">
      <object class="sizeritem">
        <object class="wxBitmapButton">
          <bitmap>fuzzy.gif</bitmap>
          <focus>fileopen.gif</focus>
        </object>
      </object>
      <object class="sizeritem">
        <object class="wxPanel">
          <object class="wxStaticText">
            <label>fdgdfgdfgdfg</label>
          </object>
          <style>wxSUNKEN_BORDER</style>
        </object>
        <flag>wxALIGN_CENTER</flag>
      </object>
      <object class="sizeritem">
        <object class="wxButton">
          <label>Buttonek</label>
        </object>
        <border>10d</border>
        <flag>wxALL</flag>
      </object>
      <object class="sizeritem">
        <object class="wxHtmlWindow">
          <htmlcode><h1>Hi,</h1>man</htmlcode>
          <size>100,45d</size>
        </object>
      </object>
      <object class="sizeritem">
        <object class="wxNotebook">
          <object class="notebookpage">
            <object class="wxPanel">
              <object class="wxBoxSizer">
                <object class="sizeritem">
                  <object class="wxHtmlWindow">
                    <htmlcode>Hello, we are inside a <u>NOTEBOOK</u>...</htmlcode>
                    <size>50,50d</size>
                  </object>
                  <option>1</option>
                </object>
              </object>
            </object>
            <label>Page</label>
          </object>
          <object class="notebookpage">
            <object class="wxPanel">
              <object class="wxBoxSizer">
                <object class="sizeritem">
                  <object class="wxHtmlWindow">
                    <htmlcode>Hello, we are inside a <u>NOTEBOOK</u>...</htmlcode>
                    <size>50,50d</size>
                  </object>
                </object>
              </object>
            </object>
            <label>Page 2</label>
          </object>
          <usenotebooksizer>1</usenotebooksizer>
        </object>
        <flag>wxEXPAND</flag>
      </object>
      <orient>wxVERTICAL</orient>
    </object>
  </object>
  <object class="wxDialog" name="dlg2">
    <object class="wxBoxSizer">
      <orient>wxVERTICAL</orient>
      <object class="sizeritem" name="dfgdfg">
        <object class="wxTextCtrl">
          <size>200,200d</size>
          <style>wxTE_MULTILINE|wxSUNKEN_BORDER</style>
          <value>Hello, this is an ordinary multiline\n         textctrl....</value>
        </object>
        <option>1</option>
        <flag>wxEXPAND|wxALL</flag>
        <border>10</border>
      </object>
      <object class="sizeritem">
        <object class="wxBoxSizer">
          <object class="sizeritem">
            <object class="wxButton" name="wxID_OK">
              <label>Ok</label>
              <default>1</default>
            </object>
          </object>
          <object class="sizeritem">
            <object class="wxButton" name="wxID_CANCEL">
              <label>Cancel</label>
            </object>
            <border>10</border>
            <flag>wxLEFT</flag>
          </object>
        </object>
        <flag>wxLEFT|wxRIGHT|wxBOTTOM|wxALIGN_RIGHT</flag>
        <border>10</border>
      </object>
    </object>
    <title>Second testing dialog</title>
  </object>
</resource>

XRC file format

Please see Technical Note 14 (docs/tech/tn0014.txt) in your wxWidgets distribution.

C++ header file generation

Using the -e switch together with -c, a C++ header file is written containing class definitions for the GUI windows defined in the XRC file. This code generation can make it easier to use XRC and automate program development. The classes can be used as basis for development, freeing the programmer from dealing with most of the XRC specifics (e.g. XRCCTRL).

For each top level window defined in the XRC file a C++ class definition is generated, containing as class members the named widgets of the window. A default constructor for each class is also generated. Inside the constructor all XRC loading is done and all class members representing widgets are initialized.

A simple example will help understand how the scheme works. Suppose you have a XRC file defining a top level window TestWnd_Base, which subclasses wxFrame (any other class like wxDialog will do also), and has subwidgets wxTextCtrl A and wxButton B. The XRC file and corresponding class definition in the header file will be something like:

<?xml version="1.0"?>
<resource version="2.3.0.1">
    <object class="wxFrame" name="TestWnd_Base">
        <size>-1,-1</size>
        <title>Test</title>
        <object class="wxBoxSizer">
            <orient>wxHORIZONTAL</orient>
            <object class="sizeritem">
                <object class="wxTextCtrl" name="A">
                    <label>Test label</label>
                </object>
            </object>
            <object class="sizeritem">
                <object class="wxButton" name="B">
                    <label>Test button</label>
                </object>
            </object>
        </object>
    </object>
</resource>


class TestWnd_Base : public wxFrame {
protected:
 wxTextCtrl* A;
 wxButton* B;

private:
 void InitWidgetsFromXRC(){
  wxXmlResource::Get()->LoadObject(this,NULL,"TestWnd","wxFrame");
  A = XRCCTRL(*this,"A",wxTextCtrl);
  B = XRCCTRL(*this,"B",wxButton);
 }
public:
TestWnd::TestWnd(){
  InitWidgetsFromXRC();
 }
};

The generated window class can be used as basis for the full window class. The class members which represent widgets may be accessed by name instead of using XRCCTRL every time you wish to reference them (note that they are protected class members), though you must still use XRCID to refer to widget IDs in the event table.

Example:

#include "resource.h"

class TestWnd : public TestWnd_Base {
	public:
		TestWnd(){
			// A, B already initialised at this point
			A->SetValue("Updated in TestWnd::TestWnd");
			B->SetValue("Nice :)");
		}
		void OnBPressed(wxEvent& event){
			Close();
		}
		DECLARE_EVENT_TABLE();
};

BEGIN_EVENT_TABLE(TestWnd,TestWnd_Base)
EVT_BUTTON(XRCID("B"),TestWnd::OnBPressed)
END_EVENT_TABLE()

Adding new resource handlers

Coming soon.