A Quick Guide to Writing Applications

Table of Contents

• Application Structure
• Drawing on the Screen
• Event Handling

Application Structure

To set a wxWidgets application going, you will need to derive a wxApp class and override wxApp::OnInit() in which you will typically create your application main top-level window.

This window can be a wxFrame or a wxDialog and may contain one or more instances of classes such as wxPanel, wxSplitterWindow or other windows and controls. These windows can be created from C++ code or loaded from resource definitions in XRC format.

A frame can have a wxMenuBar, a wxToolBar, a wxStatusBar, and a wxIcon for when the frame is iconized.

A wxPanel is used to place controls (classes derived from wxControl) which are used for user interaction. Examples of controls are wxButton, wxCheckBox, wxChoice, wxListBox, wxRadioBox, and wxSlider. Such controls need to be positioned correctly – and also repositioned when the top-level window is resized by the user – and to do this you use wxSizer-derived classes, such as wxBoxSizer and wxFlexGridSizer, to layout everything correctly.

Instances of wxDialog can also be used for controls and they have the advantage of not requiring a separate panel inside them.

Instead of creating a dialog box and populating it with items, it is possible to choose one of the convenient common dialog classes, such as wxMessageDialog and wxFileDialog.

Drawing on the Screen

You never draw directly onto a window – you use either one of the older device context (DC) classes or the newer graphics context (GC) one, that support features such as alpha transparency or anti-aliasing. wxDC is the base for wxClientDC, wxPaintDC, wxMemoryDC, wxPostScriptDC, wxMemoryDC, wxMetafileDC and wxPrinterDC. If your drawing functions have wxDC as a parameter, you can pass any of these DCs to the function, and thus use the same code to draw to several different devices. You can draw using the member functions of wxDC, such as wxDC::DrawLine and wxDC::DrawText. Control colour on a window (wxColour) with brushes (wxBrush) and pens (wxPen).

With wxGraphicsContext, you create it using one of the methods of wxGraphicsRenderer and then construct your drawing from wxGraphicsPath objects, finally using wxGraphicsContext::StrokePath() or wxGraphicsContext::FillPath().

Event Handling

GUI programs spend most of their time waiting for the user-initiated events – and then processing them. To do it, you use wxEvtHandler::Bind() to specify the handler for an event of the given time. Event handlers receive the object describing the event, such as wxKeyEvent or wxMouseEvent, and perform whichever action corresponds to it. See events handling overview for much more information about this subject.

See also

Class List by Category