The wxWidgets programming tutorial (7. Wigets part 1)

Widgets

In this chapter, we will show small examples of several widgets, available in wxWidgets. Widgets are builing blocks of our applications. wxWidgets consists of a large amout of useful widgets. Widget is a basic GUI object by definition. A widget gave wxWidgets toolkit a name. This term is used on UNIX systems. On windows, a widget is usually called a control.

wxCheckBox

wxCheckBox is a widget that has two states. On and Off. It is a box with a label. The label can be set to the right or to the left of the box. If the checkbox is checked, it is represented by a tick in a box. A checkbox can be used to show/hide splashscreen at startup, toggle visibility of a toolbar etc.

In our example, we display one checkbox on the window. We toggle the titlel of the window by clicking on the checkbox.

m_cb = new wxCheckBox(panel, ID_CHECKBOX, wxT("Show title"),

wxPoint(20, 20));

m_cb->SetValue(true);

We create a checkbox. By default, the title is visible. So we check the checkbox by calling the method SetValue().

Connect(ID_CHECKBOX, wxEVT_COMMAND_CHECKBOX_CLICKED,

wxCommandEventHandler(CheckBox::OnToggle));

If we click on the checkbox, a wxEVT_COMMAND_CHECKBOX_CLICKED event is generated. We connect this event to the user defined OnToggle() method.

if (m_cb->GetValue()) {

this->SetTitle(wxT("CheckBox"));

} else {

this->SetTitle(wxT(" "));

}

Inside the OnToggle() method, we check the state of the checkbox. If it is checked, we display "CheckBox" string in the titlebar, otherwise we clear the title.

wxBitmapButton

A bitmap button is a button, that displays a bitmap. A bitmap button can have three other states. Selected, focused and displayed. We can set a specific bitmap for those states.

In our example, we have a slider and a bitmap button. We simulate a volume control. By dragging the handle of a slider, we change a bitmap on the button.

wxImage::AddHandler( new wxPNGHandler );

We will use PNG images, so we must initialize a PNG image handler.

button = new wxBitmapButton(panel, wxID_ANY, wxBitmap(wxT("mute.png"),

wxBITMAP_TYPE_PNG), wxPoint(180, 20));

We create a bitmap button. We specify a bitmap type, in our case wxBITMAP_TYPE_PNG

pos = slider->GetValue();

We get the slider value. Depending on this value, we set a bitmap for our button. We have four volume states. Mute, minimum, medium and maximum. To change a bitmap on the button, we call the SetBitmapLabel() method.

wxToggleButton

wxToggleButton is a button that has two states. Pressed and not pressed. You toggle between these two states by clicking on it. There are situations where this functionality fits well.

In our example, we show three toggle buttons and a panel. We set the background color of the panel to black. The togglebuttons will toggle the red, green and blue parts of the color value. The background color will depend on which togglebuttons we have pressed.

colour = new wxColour(0, 0, 0);

This is the initial color value. No red, green and blue equals to black. Theoretically speaking, black is not a color after all.

m_tgbutton1 = new wxToggleButton(panel, ID_TGBUTTON1,

wxT("Red"), wxPoint(20, 20));

Here we create a toggle button.

Connect(ID_TGBUTTON1, wxEVT_COMMAND_TOGGLEBUTTON_CLICKED,

wxCommandEventHandler(ToggleButton::OnToggleRed));

If we click on the toggle button, a wxEVT_COMMAND_TOGGLEBUTTON_CLICKED event is generated. We connect the event handlers for this event. Notice, that we don't connect events to the button methods, but to the wxFrame. widget, which is a grand parent of the toggle buttons. It is possible to do this, because command events are propagated to their parents. In our case, button -> panel -> frame. If we wanted to connect the event to the button, we would have to create our derived button classe, which would mean more work.

if ( colour->Blue() ) {

colour->Set(red, green, 0);

} else {

colour->Set(red, green, 255);

}

In the event handlers, we set the respective wxColour parameters.

m_panel->SetBackgroundColour(colour->GetAsString());

We set the background of the panel.

wxStaticLine

This widget displays a simple line on the window. It can be horizontal or vertical.

In the previous example, we show Centreal European countries and their populations. The use of wxStaticLine makes it more visually attractive.

wxStaticLine *sl1 = new wxStaticLine(this, wxID_ANY, wxPoint(25, 50),

wxSize(300,1));

Here we create a horizontal static line. It is 300px wide. The height is 1px.

wxStaticText

A wxStaticText widget displays one or more lines of read-only text.

In our example, we display a part of the Eminem's Till I Collapse lyrics on the window.

wxStaticText *st = new wxStaticText(panel, wxID_ANY, text,

wxPoint(10, 10), wxDefaultSize, wxALIGN_CENTRE);

Here we create the wxStaticText widget. The static text is aligned to the cetre.

wxSlider

wxSlider is a widget that has a simple handle. This handle can be pulled back and forth. This way we are choosing a value for a specific task. Sometimes using a slider is more natural, than simply providing a number or using a spin control.

In our example, we display a slider widget. By pulling the handle of the slider, we control the background color of the panel. In such an example, using slider is more natural than using e.g. a spin control.

slider = new wxSlider(this, ID_SLIDER, 0, 0, 140, wxPoint(50, 30),

wxSize(-1, 140), wxSL_VERTICAL);

We create a vertical slider. The initial value is 0, minimal value is 0 and maximal value is 140. We display no ticks and no labels.

Connect(ID_SLIDER, wxEVT_COMMAND_SLIDER_UPDATED,

wxScrollEventHandler(MyPanel::OnScroll));

Here we connect a wxEVT_COMMAND_SLIDER_UPDATED event to the OnScroll() user defined method.

Connect(wxEVT_PAINT, wxPaintEventHandler(MyPanel::OnPaint));

We will also do some drawing, so we connect OnPaint() method to the wxEVT_PAINT event.

fill = slider->GetValue();

Refresh();

In the OnScroll() method, we will get the current slider value. We call the Refresh() method, which will generate a wxEVT_PAINT event.

dc.DrawRectangle(wxRect(140, 30, 80, 140));

dc.DrawRectangle(wxRect(140, 30, 80, fill));

Inside the OnPaint() event handler, we draw two rectangles. The first method is draws a white rectangle with a gray border. The second method draws the a rectangle with some brownish color. The height of the rectangle is controled by the fill value, which is set by the slider widget.