Binding QML Type

Enables the arbitrary creation of property bindings. More...

• List of all members, including inherited members

Properties

• delayed : bool
• property : string
• target : Object
• value : any
• when : bool

Detailed Description

In QML, property bindings result in a dependency between the properties of different objects.

Binding to an Inaccessible Property

Sometimes it is necessary to bind an object's property to that of another object that isn't directly instantiated by QML, such as a property of a class exported to QML by C++. You can use the Binding type to establish this dependency; binding any value to any object's property.

For example, in a C++ application that maps an "app.enteredText" property into QML, you can use Binding to update the enteredText property.

TextEdit { id: myTextField; text: "Please type here..." }
Binding { target: app; property: "enteredText"; value: myTextField.text }

When text changes, the C++ property enteredText will update automatically.

Conditional Bindings

In some cases you may want to modify the value of a property when a certain condition is met but leave it unmodified otherwise. Often, it's not possible to do this with direct bindings, as you have to supply values for all possible branches.

For example, the code snippet below results in a warning whenever you release the mouse. This is because the value of the binding is undefined when the mouse isn't pressed.

// produces warning: "Unable to assign [undefined] to double value"
value: if (mouse.pressed) mouse.mouseX

The Binding type can prevent this warning.

Binding on value {
    when: mouse.pressed
    value: mouse.mouseX
}

The Binding type restores any previously set direct bindings on the property.

See also Qt QML.

Property Documentation

Binding {
    target: contactName; property: 'text'
    value: givenName + " " + familyName; when: list.ListView.isCurrentItem
    delayed: true
}

Item {
    id: item

    property rect rectangle: Qt.rect(0, 0, 200, 200)
}

Binding {
    target: item
    property: "rectangle.x"
    value: 100
}

Binding {
    target: contactName; property: 'text'
    value: name; when: list.ListView.isCurrentItem
}