.NET/Java PDF, Tiff, Barcode SDK Library

Behaviors are enormously powerful and immensely useful aspects of the Atlas framework that you can use to give your applications more sophisticated GUIs but keep them easy to develop and maintain. You looked at how to use the click behavior to add click event handling to elements that may not normally have this, enable more complex functionality to be implemented on simple elements such as <div> tags, and make them clickable without needing to use buttons or custom JavaScript hyperlink workarounds. Next, you looked at the behaviors that allow for mouse hovering and hot tracking. This allows you to update your UI or implement features such as tooltips that improve the user experience upon hovering over various elements of the page. You saw how you can use these behaviors to trigger style updates or implement custom actions. You used this to implement a pop-up menu that contained a list of hyperlinks. You could use such functionality to implement custom smart tags on your pages, context menus, or more. Finally, you extended on the floatingWindow behavior that was used for the pop-up menu to learn how easy it is to implement panes that can be dragged and dropped across your page. Ultimately, behaviors give you the facility to implement complex GUI functionality without explicitly coding it. As you progress through this book, you will see where the behaviors are used extensively to empower the GUI.

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Summary

Windows Forms provides a .NET wrapper around the Win32 user interface model. Visible elements are represented as objects that derive from the Control base class. Control features are configured with normal .NET properties, and we can use ordinary C# event handlers to respond to user input. Data binding automates some aspects of connecting data to the screen, although the support in Windows Forms is not as comprehensive as in WPF, and we needed to do some extra work to get the effect we required on the control we wanted to use. Windows Forms may be less powerful than WPF, but it has a smaller memory footprint and may be more suitable on low-end hardware, or if you need to use controls that are available only for Windows Forms.

Because the widget is painted by the code, the paintEvent needs to be reimplemented. You will also need to reimplement the wheelEvent because you want to listen to mouse wheel activity. I chose to add a heightForWidth function, which will be used to keep the widget square, and a sizeHint method that gives it a nice starting size. All this is summarized in the class declaration shown in Listing 6-19. Listing 6-19. The class declaration of the CircleBar widget class class CircleBar : public QWidget { Q_OBJECT public: CircleBar( int value = 0, QWidget *parent = 0 ); int value() const; int heightForWidth( int ) const; QSize sizeHint() const; public slots: void setValue( int ); signals: void valueChanged( int ); protected: void paintEvent( QPaintEvent* ); void wheelEvent( QWheelEvent* ); private: int m_value; }; The constructor of the CircleBar class shown in Listing 6-20 starts by initializing the internal value that is kept in the m_value member. It also creates a new size policy that is preferred in both directions and tells the layout management system to listen to the heightForWidth method. Listing 6-20. The constructor of the CircleBar widget CircleBar::CircleBar( int value, QWidget *parent ) : QWidget( parent ) { m_value = value; QSizePolicy policy( QSizePolicy::Preferred, QSizePolicy::Preferred ); policy.setHeightForWidth( true ); setSizePolicy( policy ); }

A constructor is a special method which allows you to perform some setup when you create an instance of a class. Just like any other method, you can provide it with parameters, but it doesn t have an explicit return value. Constructors always have the same name as their containing class. Example 3-6 adds a constructor that takes the plane s identifier. Because the constructor is a member of the class, it s allowed to use the Identifier property s private setter.

class Plane { public Plane(string newIdentifier) { Identifier = newIdentifier; } public string Identifier { get; private set; }

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