QDoubleSpinBox Class | Qt Widgets 5.15.2

- Qt 5.15
- Qt Widgets
- C++ Classes
- QDoubleSpinBox
- Qt 5.15.2 Reference Documentation

# QDoubleSpinBox Class

The QDoubleSpinBox class provides a spin box widget that takes doubles. More...

Header: | #include <QDoubleSpinBox>
qmake: | QT += widgets
Inherits: | QAbstractSpinBox

- List of all members, including inherited members
- Obsolete members

## Properties

- cleanText : const QString
- decimals : int
- maximum : double
- minimum : double
- prefix : QString

- singleStep : double
- stepType : StepType
- suffix : QString
- value : double

## Public Functions

| QDoubleSpinBox(QWidget *parent = nullptr)
virtual | ~QDoubleSpinBox()
QString | cleanText() const
int | decimals() const
double | maximum() const
double | minimum() const
QString | prefix() const
void | setDecimals(int prec)
void | setMaximum(double max)
void | setMinimum(double min)
void | setPrefix(const QString &prefix)
void | setRange(double minimum, double maximum)
void | setSingleStep(double val)
void | setStepType(QAbstractSpinBox::StepType stepType)
void | setSuffix(const QString &suffix)
double | singleStep() const
QAbstractSpinBox::StepType | stepType() const
QString | suffix() const
virtual QString | textFromValue(double value) const
double | value() const
virtual double | valueFromText(const QString &text) const

## Reimplemented Public Functions

virtual void | fixup(QString &input) const override
virtual QValidator::State | validate(QString &text, int &pos) const override

## Public Slots

void | setValue(double val)

## Signals

void | textChanged(const QString &text)
void | valueChanged(double d)

## Detailed Description

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

Every time the value changes QDoubleSpinBox emits valueChanged() and textChanged() signals, the former providing a double and the latter a QString. The textChanged() signal provides the value with both prefix() and suffix(). The current value can be fetched with value() and set with setValue().

Note: QDoubleSpinBox will round numbers so they can be displayed with the current precision. In a QDoubleSpinBox with decimals set to 2, calling setValue(2.555) will cause value() to return 2.56.

Clicking the up and 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 behavior 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(). The spinbox has a default precision of 2 decimal places but this can be changed using setDecimals().

Most spin boxes are directional, but QDoubleSpinBox can also operate as a circular spin box, i.e. if the range is 0.0-99.9 and the current value is 99.9, 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 QDoubleSpinBox.

Note: The displayed value of the QDoubleSpinBox is limited to 18 characters in addition to eventual prefix and suffix content. This limitation is used to keep the double spin box usable even with extremely large values.

See also QSpinBox, 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:

QString | cleanText() const

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

### decimals : int

This property holds the precision of the spin box, in decimals

Sets how many decimals the spinbox will use for displaying and interpreting doubles.

Warning: The maximum value for decimals is DBL_MAX_10_EXP + DBL_DIG (ie. 323) because of the limitations of the double type.

Note: The maximum, minimum and value might change as a result of changing this property.

Access functions:

int | decimals() const
void | setDecimals(int prec)

### maximum : double

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 99.99.

Note: The maximum value will be rounded to match the decimals property.

Access functions:

double | maximum() const
void | setMaximum(double max)

See also decimals and setRange().

### minimum : double

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 0.0.

Note: The minimum value will be rounded to match the decimals property.

Access functions:

double | minimum() const
void | setMinimum(double min)

See also decimals, setRange(), and specialValueText.

### prefix : QString

This property holds the spin box's prefix

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:

     spinbox->setPrefix("$");

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:

QString | prefix() const
void | setPrefix(const QString &prefix)

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

### singleStep : double

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 1.0. Setting a singleStep value of less than 0 does nothing.

Access functions:

double | singleStep() const
void | setSingleStep(double val)

### stepType : StepType

This property holds the step type.

The step type can be single step or adaptive decimal step.

Access functions:

QAbstractSpinBox::StepType | stepType() const
void | setStepType(QAbstractSpinBox::StepType stepType)

### 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:

     spinbox->setSuffix(" km");

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:

QString | suffix() const
void | setSuffix(const QString &suffix)

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

### value : double

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.

Note: The value will be rounded so it can be displayed with the current setting of decimals.

Access functions:

double | value() const
void | setValue(double val)

Notifier signal:

void | valueChanged(double d)

See also decimals.

## Member Function Documentation

### QDoubleSpinBox::QDoubleSpinBox(QWidget *parent = nullptr)

Constructs a spin box with 0.0 as minimum value and 99.99 as maximum value, a step value of 1.0 and a precision of 2 decimal places. The value is initially set to 0.00. The spin box has the given parent.

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

### `[signal]` void QDoubleSpinBox::textChanged(const QString &text)

This signal is emitted whenever the spin box's text is changed. The new text is passed in text with prefix() and suffix().

This function was introduced in Qt 5.14.

### `[signal]` void QDoubleSpinBox::valueChanged(double d)

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

Note: Notifier signal for property value.

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:

     connect(doubleSpinBox, QOverload<double>::of(&QDoubleSpinBox::valueChanged),
         [=](double d){ /* ... */ });

### `[virtual]` QDoubleSpinBox::~QDoubleSpinBox()

Destructor.

### `[override virtual]` void QDoubleSpinBox::fixup(QString &input) const

Reimplements: QAbstractSpinBox::fixup(QString &input) const.

### void QDoubleSpinBox::setRange(double minimum, double maximum)

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

Note: The maximum and minimum values will be rounded to match the decimals property.

     setRange(minimum, maximum);

is equivalent to:

     setMinimum(minimum);
     setMaximum(maximum);

See also minimum and maximum.

### void QDoubleSpinBox::setStepType(QAbstractSpinBox::StepType stepType)

Sets the step type for the spin box to stepType, which is single step or adaptive decimal step.

Adaptive decimal step means that the step size will continuously be adjusted to one power of ten below the current value. So when the value is 1100, the step is set to 100, so stepping up once increases it to 1200. For 1200 stepping up takes it to 1300. For negative values, stepping down from -1100 goes to -1200.

It also works for any decimal values, 0.041 is increased to 0.042 by stepping once.

Step direction is taken into account to handle edges cases, so that stepping down from 100 takes the value to 99 instead of 90. Thus a step up followed by a step down -- or vice versa -- always lands on the starting value; 99 -> 100 -> 99.

Setting this will cause the spin box to disregard the value of singleStep, although it is preserved so that singleStep comes into effect if adaptive decimal step is later turned off.

Note: Setter function for property stepType.

This function was introduced in Qt 5.12.

See also stepType().

### `[virtual]` QString QDoubleSpinBox::textFromValue(double value) 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 using QWidget::locale().toString(value, QLatin1Char('f'), decimals()) and will remove the thousand separator unless setGroupSeparatorShown() is set. Reimplementations may return anything.

Note: QDoubleSpinBox 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().

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

### `[override virtual]` QValidator::State QDoubleSpinBox::validate(QString &text, int &pos) const

Reimplements: QAbstractSpinBox::validate(QString &input, int &pos) const.

### `[virtual]` double QDoubleSpinBox::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: QDoubleSpinBox handles specialValueText() separately; this function is only concerned with the other values.

See also textFromValue() and validate().