• Can Qt Slot Return Value Calculator
• Can Qt Slot Return Value Guide

1. While QML in Qt 5 has some shortcuts for a few selected properties, some properties might end up going through the generic property interface of QObject. The numbers in the first line of the table reflect the worst and best case performance we can get in Qt 5.15. The other lines show the performance we can get in Qt 6.
2. According to the documentation the return value from a slot doesn't mean anything. Yet in the generated moc code I see that if a slot returns a value this value is used for something. Any idea what does it do?

You can see that you have to provide a signature inside the SIGNAL and SLOT macro, providing the type of the values that are passed through the signals. You may also provide the name of the variable if you want. (It is actually even better). Features of signals and slots. A signal can be connected to several slots; Many signals can be connected. Def importpyqt5: ' Import PyQt5 ImportErrors raised within this function are non-recoverable ' from PyQt5 import QtGui, QtCore, QtSvg # Alias PyQt-specific functions for PySide compatibility. QtCore.Signal = QtCore.pyqtSignal QtCore.Slot = QtCore.pyqtSlot return QtCore, QtGui, QtSvg, QTAPIPYQT5. Edit: I think I just realized that you meant the function is not in a class, right? If that is the case, I don't know of a way to make that work. Qt is heavily object-oriented and I think you can only call slots and signals on objects. Last edited by scio (2009-04-21 12:26:44).

The QSpinBox class provides a spin box widget. More...

Properties

• 12 properties inherited from QAbstractSpinBox
• 59 properties inherited from QWidget
• 1 property inherited from QObject

Public Functions

• 30 public functions inherited from QAbstractSpinBox
• 214 public functions inherited from QWidget
• 32 public functions inherited from QObject
• 14 public functions inherited from QPaintDevice

Public Slots

• 4 public slots inherited from QAbstractSpinBox
• 19 public slots inherited from QWidget
• 1 public slot inherited from QObject

Signals

• 1 signal inherited from QAbstractSpinBox
• 3 signals inherited from QWidget
• 2 signals inherited from QObject

Protected Functions

Reimplemented Protected Functions

• 20 protected functions inherited from QAbstractSpinBox
• 35 protected functions inherited from QWidget
• 9 protected functions inherited from QObject
• 1 protected function inherited from QPaintDevice

Additional Inherited Members

• 5 static public members inherited from QWidget
• 11 static public members inherited from QObject
• 1 protected slot inherited from QWidget

Detailed Description

The QSpinBox class provides a spin box widget.

QSpinBox is designed to handle integers and discrete sets of values (e.g., month names); use QDoubleSpinBox for floating point values.

QSpinBox allows the user to choose a value by clicking the up/down buttons or pressing up/down on the keyboard to increase/decrease the value currently displayed. The user can also type the value in manually. The spin box supports integer values but can be extended to use different strings with validate(), textFromValue() and valueFromText().

Every time the value changes QSpinBox emits two valueChanged() signals, one providing an int and the other a QString. The QString overload provides the value with both prefix() and suffix(). The current value can be fetched with value() and set with setValue().

Clicking the up/down buttons or using the keyboard accelerator's up and down arrows will increase or decrease the current value in steps of size singleStep(). If you want to change this behaviour you can reimplement the virtual function stepBy(). The minimum and maximum value and the step size can be set using one of the constructors, and can be changed later with setMinimum(), setMaximum() and setSingleStep().

Most spin boxes are directional, but QSpinBox can also operate as a circular spin box, i.e. if the range is 0-99 and the current value is 99, clicking 'up' will give 0 if wrapping() is set to true. Use setWrapping() if you want circular behavior.

The displayed value can be prepended and appended with arbitrary strings indicating, for example, currency or the unit of measurement. See setPrefix() and setSuffix(). The text in the spin box is retrieved with text() (which includes any prefix() and suffix()), or with cleanText() (which has no prefix(), no suffix() and no leading or trailing whitespace).

It is often desirable to give the user a special (often default) choice in addition to the range of numeric values. See setSpecialValueText() for how to do this with QSpinBox.

Subclassing QSpinBox

If using prefix(), suffix(), and specialValueText() don't provide enough control, you subclass QSpinBox and reimplement valueFromText() and textFromValue(). For example, here's the code for a custom spin box that allows the user to enter icon sizes (e.g., '32 x 32'):

See the Icons example for the full source code.

See also QDoubleSpinBox, QDateTimeEdit, QSlider, and Spin Boxes Example.

Property Documentation

cleanText : const QString

This property holds the text of the spin box excluding any prefix, suffix, or leading or trailing whitespace.

Access functions:

See also text, QSpinBox::prefix, and QSpinBox::suffix.

displayIntegerBase : int

This property holds the base used to display the value of the spin box

The default displayIntegerBase value is 10.

This property was introduced in Qt 5.2.

Access functions:

See also textFromValue() and valueFromText().

maximum : int

This property holds the maximum value of the spin box

When setting this property the minimum is adjusted if necessary, to ensure that the range remains valid.

The default maximum value is 99.

Access functions:

See also setRange() and specialValueText.

minimum : int

This property holds the minimum value of the spin box

When setting this property the maximum is adjusted if necessary to ensure that the range remains valid.

The default minimum value is 0.

Access functions:

See also setRange() and specialValueText.

prefix : QString

This property holds the spin box's prefix

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The prefix is prepended to the start of the displayed value. Typical use is to display a unit of measurement or a currency symbol. For example:

To turn off the prefix display, set this property to an empty string. The default is no prefix. The prefix is not displayed when value() minimum() and specialValueText() is set.

If no prefix is set, prefix() returns an empty string.

Access functions:

See also suffix(), setSuffix(), specialValueText(), and setSpecialValueText().

singleStep : int

This property holds the step value

When the user uses the arrows to change the spin box's value the value will be incremented/decremented by the amount of the singleStep. The default value is 1. Setting a singleStep value of less than 0 does nothing.

Access functions:

Can Qt Slot Return Value Guide

suffix : QString

This property holds the suffix of the spin box

The suffix is appended to the end of the displayed value. Typical use is to display a unit of measurement or a currency symbol. For example:

To turn off the suffix display, set this property to an empty string. The default is no suffix. The suffix is not displayed for the minimum() if specialValueText() is set.

If no suffix is set, suffix() returns an empty string.

Access functions:

See also prefix(), setPrefix(), specialValueText(), and setSpecialValueText().

value : int

This property holds the value of the spin box

setValue() will emit valueChanged() if the new value is different from the old one. The value property has a second notifier signal which includes the spin box's prefix and suffix.

Access functions:

Notifier signal:

Member Function Documentation

QSpinBox::QSpinBox(QWidget *parent = Q_NULLPTR)

Constructs a spin box with 0 as minimum value and 99 as maximum value, a step value of 1. The value is initially set to 0. It is parented to parent.

See also setMinimum(), setMaximum(), and setSingleStep().

QSpinBox::~QSpinBox()

Destructor.

[override virtual protected] bool QSpinBox::event(QEvent *event)

Reimplemented from QObject::event().

[override virtual protected] void QSpinBox::fixup(QString &input) const

Reimplemented from QAbstractSpinBox::fixup().

void QSpinBox::setRange(intminimum, intmaximum)

Convenience function to set the minimum, and maximum values with a single function call.

is equivalent to:

See also minimum and maximum.

[virtual protected] QString QSpinBox::textFromValue(intvalue) const

This virtual function is used by the spin box whenever it needs to display the given value. The default implementation returns a string containing value printed in the standard way using QWidget::locale().toString(), but with the thousand separator removed unless setGroupSeparatorShown() is set. Reimplementations may return anything. (See the example in the detailed description.)

Note: QSpinBox does not call this function for specialValueText() and that neither prefix() nor suffix() should be included in the return value.

If you reimplement this, you may also need to reimplement valueFromText() and validate()

See also valueFromText(), validate(), and QLocale::groupSeparator().

[override virtual protected] QValidator::State QSpinBox::validate(QString &text, int &pos) const

Reimplemented from QAbstractSpinBox::validate().

[signal] void QSpinBox::valueChanged(inti)

This signal is emitted whenever the spin box's value is changed. The new value's integer value is passed in i.

Note: Signal valueChanged is overloaded in this class. To connect to this signal by using the function pointer syntax, Qt provides a convenient helper for obtaining the function pointer as shown in this example:

Note: Notifier signal for property value.

[signal] void QSpinBox::valueChanged(const QString &text)

This is an overloaded function.

The new value is passed in text with prefix() and suffix().

Note: Signal valueChanged is overloaded in this class. To connect to this signal by using the function pointer syntax, Qt provides a convenient helper for obtaining the function pointer as shown in this example:

Note: Notifier signal for property value.

[virtual protected] int QSpinBox::valueFromText(const QString &text) const

This virtual function is used by the spin box whenever it needs to interpret text entered by the user as a value.

Subclasses that need to display spin box values in a non-numeric way need to reimplement this function.

Note: QSpinBox handles specialValueText() separately; this function is only concerned with the other values.

See also textFromValue() and validate().

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