Detailed Description
The QDial class provides a rounded range control (like a speedometer or potentiometer).
QDial is used when the user needs to control a value within a program-definable range, and the range either wraps around (typically, 0..359 degrees) or the dialog layout needs a square widget.
Both API- and UI-wise, the dial is very similar to a slider. Indeed, when wrapping() is false (the default) there is no real difference between a slider and a dial. They have the same signals, slots and member functions, all of which do the same things. Which one you use depends only on your taste and on the application.
The dial initially emits valueChanged() signals continuously while the slider is being moved; you can make it emit the signal less often by calling setTracking(false). dialMoved() is emitted continuously even when tracking() is false.
The slider also emits dialPressed() and dialReleased() signals when the mouse button is pressed and released. But note that the dial's value can change without these signals being emitted; the keyboard and wheel can be used to change the value.
Unlike the slider, QDial attempts to draw a "nice" number of notches rather than one per lineStep(). If possible, the number of notches drawn is one per lineStep(), but if there aren't enough pixels to draw every one, QDial will draw every second, third etc., notch. notchSize() returns the number of units per notch, hopefully a multiple of lineStep(); setNotchTarget() sets the target distance between neighbouring notches in pixels. The default is 3.75 pixels.
Like the slider, the dial makes the QAbstractSlider functions setValue(), addLine(), subtractLine(), addPage() and subtractPage() available as slots.
The dial's keyboard interface is fairly simple: The left/up and right/down arrow keys move by lineStep(), page up and page down by pageStep() and Home and End to minValue() and maxValue().
See also QScrollBar, QSpinBox, and GUI Design Handbook: Slider.
Property Documentation
notchSize : const int
This property holds the current notch size.
The notch size is in range control units, not pixels, and if possible it is a multiple of lineStep() that results in an on-screen notch size near notchTarget().
Access functions:
See also notchTarget() and lineStep().
notchTarget : qreal
This property holds the target number of pixels between notches.
The notch target is the number of pixels QDial attempts to put between each notch.
The actual size may differ from the target size.
Access functions:
- qreal notchTarget () const
- void setNotchTarget ( double target )
notchesVisible : bool
This property holds whether the notches are shown.
If true, the notches are shown. If false (the default) notches are not shown.
Access functions:
- bool notchesVisible () const
- void setNotchesVisible ( bool visible )
wrapping : bool
This property holds whether wrapping is enabled.
If true, wrapping is enabled. This means that the arrow can be turned around 360 degrees. Otherwise there is some space at the bottom of the dial which is skipped by the arrow.
This property's default is false.
Access functions:
- bool wrapping () const
- void setWrapping ( bool on )
Member Function Documentation
QDial::QDial ( QWidget * parent = 0 )
Constructs a dial.
The parent argument is sent to the QAbstractSlider constructor.
QDial::~QDial ()
Destroys the dial.
