Binding

open class Binding : Object, BindingProtocol

The Binding type acts as a reference-counted owner of an underlying GBinding instance. It provides the methods that can operate on this data type through BindingProtocol conformance. Use Binding as a strong reference or owner of a GBinding instance.

GBinding is the representation of a binding between a property on a GObject instance (or source) and another property on another GObject instance (or target). Whenever the source property changes, the same value is applied to the target property; for instance, the following binding:

(C Language Example):

  g_object_bind_property (object1, "property-a",
                          object2, "property-b",
                          G_BINDING_DEFAULT);

will cause the property named “property-b” of object2 to be updated every time g_object_set() or the specific accessor changes the value of the property “property-a” of object1.

It is possible to create a bidirectional binding between two properties of two GObject instances, so that if either property changes, the other is updated as well, for instance:

(C Language Example):

  g_object_bind_property (object1, "property-a",
                          object2, "property-b",
                          G_BINDING_BIDIRECTIONAL);

will keep the two properties in sync.

It is also possible to set a custom transformation function (in both directions, in case of a bidirectional binding) to apply a custom transformation from the source value to the target value before applying it; for instance, the following binding:

(C Language Example):

  g_object_bind_property_full (adjustment1, "value",
                               adjustment2, "value",
                               G_BINDING_BIDIRECTIONAL,
                               celsius_to_fahrenheit,
                               fahrenheit_to_celsius,
                               NULL, NULL);

will keep the “value” property of the two adjustments in sync; the celsius_to_fahrenheit function will be called whenever the “value” property of adjustment1 changes and will transform the current value of the property before applying it to the “value” property of adjustment2.

Vice versa, the fahrenheit_to_celsius function will be called whenever the “value” property of adjustment2 changes, and will transform the current value of the property before applying it to the “value” property of adjustment1.

Note that GBinding does not resolve cycles by itself; a cycle like

  object1:propertyA -> object2:propertyB
  object2:propertyB -> object3:propertyC
  object3:propertyC -> object1:propertyA

might lead to an infinite loop. The loop, in this particular case, can be avoided if the objects emit the GObject::notify signal only if the value has effectively been changed. A binding is implemented using the GObject::notify signal, so it is susceptible to all the various ways of blocking a signal emission, like g_signal_stop_emission() or g_signal_handler_block().

A binding will be severed, and the resources it allocates freed, whenever either one of the GObject instances it refers to are finalized, or when the GBinding instance loses its last reference.

Bindings for languages with garbage collection can use g_binding_unbind() to explicitly release a binding between the source and target properties, instead of relying on the last reference on the binding, source, and target instances to drop.

GBinding is available since GObject 2.26

  • Designated initialiser from the underlying `C` data type.
    

    This creates an instance without performing an unbalanced retain i.e., ownership is transferred to the Binding instance.

    Declaration

    Swift

    public init(_ op: UnsafeMutablePointer<GBinding>)

    Parameters

    op

    pointer to the underlying object

  • Designated initialiser from the underlying C data type. Will retain GBinding. i.e., ownership is transferred to the Binding instance.

    Declaration

    Swift

    public init(retaining op: UnsafeMutablePointer<GBinding>)

    Parameters

    op

    pointer to the underlying object

  • Reference intialiser for a related type that implements BindingProtocol Will retain GBinding.

    Declaration

    Swift

    public init<T>(binding other: T) where T : BindingProtocol

    Parameters

    other

    an instance of a related type that implements BindingProtocol

  • Unsafe typed initialiser. Do not use unless you know the underlying data type the pointer points to conforms to BindingProtocol.

    Declaration

    Swift

    override public init<T>(cPointer p: UnsafeMutablePointer<T>)

    Parameters

    cPointer

    pointer to the underlying object

  • Unsafe typed, retaining initialiser. Do not use unless you know the underlying data type the pointer points to conforms to BindingProtocol.

    Declaration

    Swift

    override public init<T>(retainingCPointer cPointer: UnsafeMutablePointer<T>)

    Parameters

    cPointer

    pointer to the underlying object

  • Unsafe untyped initialiser. Do not use unless you know the underlying data type the pointer points to conforms to BindingProtocol.

    Declaration

    Swift

    override public init(raw p: UnsafeRawPointer)

    Parameters

    p

    raw pointer to the underlying object

  • Unsafe untyped, retaining initialiser. Do not use unless you know the underlying data type the pointer points to conforms to BindingProtocol.

    Declaration

    Swift

    override public init(retainingRaw raw: UnsafeRawPointer)
  • Unsafe untyped initialiser. Do not use unless you know the underlying data type the pointer points to conforms to BindingProtocol.

    Declaration

    Swift

    override public init(raw p: UnsafeMutableRawPointer)

    Parameters

    p

    mutable raw pointer to the underlying object

  • Unsafe untyped, retaining initialiser. Do not use unless you know the underlying data type the pointer points to conforms to BindingProtocol.

    Declaration

    Swift

    override public init(retainingRaw raw: UnsafeMutableRawPointer)

    Parameters

    raw

    mutable raw pointer to the underlying object

  • Unsafe untyped initialiser. Do not use unless you know the underlying data type the pointer points to conforms to BindingProtocol.

    Declaration

    Swift

    override public init(opaquePointer p: OpaquePointer)

    Parameters

    p

    opaque pointer to the underlying object

  • Unsafe untyped, retaining initialiser. Do not use unless you know the underlying data type the pointer points to conforms to BindingProtocol.

    Declaration

    Swift

    override public init(retainingOpaquePointer p: OpaquePointer)

    Parameters

    p

    opaque pointer to the underlying object