6. Widget Creation

When a developer finds that the existing widgets are no longer useful, they may find the need to create new widgets. This is a common task while developing GUIs.

Tip

The ELT Control GUI Toolkit Design includes more information on how to use existing widgets.

A new widget usually falls into the following three categories.

New Widget

When a new more of display or interaction is needed, and there is not currently available widget that can meet the requirements, then a completely new widget is needed. This kind of widgets are for example, the DartBoard and the Analog Clock.

Specialize Existing Widget

If an existing widget matches closely the representation and interaction capabilities of an existing widget, it is recommended to specialize the similar widget.

Composite Widget

When developing complex UIs, it is a common task to create a widget than contains a set of widgets. This commonly represent real world concepts such as a Motor, or can be used to present several monitor points.

We include also a section that discusses topics common to all kind of widgets.

• 6.1. Common to all kind of widgets
  • 6.1.1. Widget Class Declaration
  • 6.1.2. WAF project/module for the Widget
• 6.2. Creating a New Widget
  • 6.2.1. update() and paintEvent() methods
  • 6.2.2. event(QEvent*) and specialized event methods
  • 6.2.3. Colors and Palette
  • 6.2.4. Fonts
  • 6.2.5. Coordinates
  • 6.2.6. save() and restore()
  • 6.2.7. Widget Size and Ratio
  • 6.2.8. Caching Pixmaps
  • 6.2.9. Plugin, Bindings and Example Application
• 6.3. Specialize an Existing Widget
  • 6.3.1. Declaration
  • 6.3.2. Implementation
• 6.4. Create a Composite Widget from Existing Ones
  • 6.4.1. UI Declaration
  • 6.4.2. Widget Class