Binding
open class Binding : Object, BindingProtocol
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
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.
-
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
@inlinable public init(_ op: UnsafeMutablePointer<GBinding>)
Parameters
op
pointer to the underlying object
-
Designated initialiser from a constant pointer to the underlying
C
data type. This creates an instance without performing an unbalanced retain i.e., ownership is transferred to theBinding
instance.Declaration
Swift
@inlinable public init(_ op: UnsafePointer<GBinding>)
Parameters
op
pointer to the underlying object
-
Optional initialiser from a non-mutating
gpointer
to the underlyingC
data type. This creates an instance without performing an unbalanced retain i.e., ownership is transferred to theBinding
instance.Declaration
Swift
@inlinable override public init!(gpointer op: gpointer?)
Parameters
op
gpointer to the underlying object
-
Optional initialiser from a non-mutating
gconstpointer
to the underlyingC
data type. This creates an instance without performing an unbalanced retain i.e., ownership is transferred to theBinding
instance.Declaration
Swift
@inlinable override public init!(gconstpointer op: gconstpointer?)
Parameters
op
pointer to the underlying object
-
Optional initialiser from a constant pointer to the underlying
C
data type. This creates an instance without performing an unbalanced retain i.e., ownership is transferred to theBinding
instance.Declaration
Swift
@inlinable public init!(_ op: UnsafePointer<GBinding>?)
Parameters
op
pointer to the underlying object
-
Optional initialiser from the underlying
C
data type. This creates an instance without performing an unbalanced retain i.e., ownership is transferred to theBinding
instance.Declaration
Swift
@inlinable public init!(_ op: UnsafeMutablePointer<GBinding>?)
Parameters
op
pointer to the underlying object
-
Designated initialiser from the underlying
C
data type. Will retainGBinding
. i.e., ownership is transferred to theBinding
instance.Declaration
Swift
@inlinable public init(retaining op: UnsafeMutablePointer<GBinding>)
Parameters
op
pointer to the underlying object
-
Reference intialiser for a related type that implements
BindingProtocol
Will retainGBinding
.Declaration
Swift
@inlinable 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
@inlinable 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
@inlinable 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
@inlinable 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
@inlinable 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
@inlinable public required 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
@inlinable required 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
@inlinable 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
@inlinable override public init(retainingOpaquePointer p: OpaquePointer)
Parameters
p
opaque pointer to the underlying object