- Qt 6.8
- Qt Core
- C++ Classes
- QBindable
- Qt 6.8.3 Reference Documentation

# QBindable Class

template <typename T> class QBindable

QBindable is a wrapper class around binding-enabled properties. It allows type-safe operations while abstracting the differences between the various property classes away. More...

Header: | `#include <QBindable>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Core)` `target_link_libraries(mytarget PRIVATE Qt6::Core)`
qmake: | `QT += core`
Inherits: | QUntypedBindable

- List of all members, including inherited members

## Public Functions

| QBindable(QObject *obj, const QMetaProperty &property)
| QBindable(QObject *obj, const char *property)
QPropertyBinding<T> | binding() const
QPropertyBinding<T> | makeBinding(const QPropertyBindingSourceLocation &location = QT_PROPERTY_DEFAULT_BINDING_LOCATION) const
QPropertyBinding<T> | setBinding(const QPropertyBinding<T> &binding)
QPropertyBinding<T> | setBinding(Functor f)
void | setValue(const T &value)
QPropertyBinding<T> | takeBinding()
T | value() const

## Detailed Description

QBindable<T> helps to integrate Qt's traditional Q_PROPERTY with binding-enabled properties. If a property is backed by a QProperty, QObjectBindableProperty or QObjectComputedProperty, you can add `BINDABLE` bindablePropertyName to the Q_PROPERTY declaration, where bindablePropertyName is a function returning an instance of QBindable constructed from the QProperty. The returned QBindable allows users of the property to set and query bindings of the property, without having to know the exact kind of binding-enabled property used.

     class MyClass : public QObject
     {
         Q_OBJECT
         Q_PROPERTY(int x READ x WRITE setX NOTIFY xChanged BINDABLE bindableX)
     public:
         int x() const { return xProp; }
         void setX(int x) { xProp = x; }
         QBindable<int> bindableX() { return QBindable<int>(&xProp); }

     signals:
         void xChanged();

     private:
         // Declare the instance of the bindable property data.
         Q_OBJECT_BINDABLE_PROPERTY(MyClass, int, xProp, &MyClass::xChanged)
     };
     MyClass *myObject;
     QBindable<int> bindableX = myObject->bindableX();
     qDebug() << bindableX.hasBinding(); // prints false
     QProperty<int> y {42};
     bindableX.setBinding([&](){ return 2*y.value(); });
     qDebug() << bindableX.hasBinding() << myObject->x(); // prints true 84

See also QMetaProperty::isBindable, QProperty, QObjectBindableProperty, QObjectComputedProperty, and Qt Bindable Properties.

## Member Function Documentation

### `[explicit]` QBindable::QBindable(QObject *obj, const QMetaProperty &property)

See QBindable::QBindable(QObject *obj, const char *property)

### `[explicit]` QBindable::QBindable(QObject *obj, const char *property)

Constructs a QBindable for the Q_PROPERTY property on obj. The property must have a notify signal but does not need to have `BINDABLE` in its `Q_PROPERTY` definition, so even binding unaware `Q_PROPERTY`s can be bound or used in binding expressions. You must use `QBindable::value()` in binding expressions instead of the normal property `READ` function (or `MEMBER`) to enable dependency tracking if the property is not `BINDABLE`. When binding using a lambda, you may prefer to capture the QBindable by value to avoid the cost of calling this constructor in the binding expression. This constructor should not be used to implement `BINDABLE` for a Q_PROPERTY, as the resulting Q_PROPERTY will not support dependency tracking. To make a property that is usable directly without reading through a QBindable use QProperty or QObjectBindableProperty.

     QProperty<QString> displayText;
     QDateTimeEdit *dateTimeEdit = findDateTimeEdit();
     QBindable<QDateTime> dateTimeBindable(dateTimeEdit, "dateTime");
     displayText.setBinding([dateTimeBindable](){ return dateTimeBindable.value().toString(); });

See also QProperty, QObjectBindableProperty, and Qt Bindable Properties.

### QPropertyBinding<T> QBindable::binding() const

Returns the currently set binding of the underlying property. If the property does not have a binding, the returned `QPropertyBinding<T>` will be invalid.

See also setBinding and hasBinding.

### QPropertyBinding<T> QBindable::makeBinding(const QPropertyBindingSourceLocation &location = QT_PROPERTY_DEFAULT_BINDING_LOCATION) const

Constructs a binding evaluating to the underlying property's value, using a specified source location.

### QPropertyBinding<T> QBindable::setBinding(const QPropertyBinding<T> &binding)

Sets the underlying property's binding to binding. Does nothing if the QBindable is read-only or invalid.

See also binding, isReadOnly(), and isValid().

### template <typename Functor> QPropertyBinding<T> QBindable::setBinding(Functor f)

This is an overloaded function.

Creates a `QPropertyBinding<T>` from f, and sets it as the underlying property's binding.

### void QBindable::setValue(const T &value)

Sets the underlying property's value to value. This removes any currenltly set binding from it. This function has no effect if the QBindable is read-only or invalid.

See also value(), isValid(), isReadOnly(), and setBinding().

### QPropertyBinding<T> QBindable::takeBinding()

Removes the currently set binding of the underlying property and returns it. If the property does not have a binding, the returned `QPropertyBinding<T>` will be invalid.

See also binding, setBinding, and hasBinding.

### T QBindable::value() const

Returns the underlying property's current value. If the QBindable is invalid, a default constructed `T` is returned.

See also setValue() and isValid().