Binding

Added in version 2.26.

class Binding(**properties: Any)

Superclasses: Object

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:

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 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:

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:

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 Binding 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 signal_stop_emission or 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 Binding instance loses its last reference.

Bindings for languages with garbage collection can use 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.

Methods

class Binding

unbind()

Explicitly releases the binding between the source and the target property expressed by binding.

This function will release the reference that is being held on the binding instance if the binding is still bound; if you want to hold on to the Binding instance after calling unbind(), you will need to hold a reference to it.

Note however that this function does not take ownership of binding, it only unrefs the reference that was initially created by bind_property() and is owned by the binding.

Added in version 2.38.

Properties

class Binding

props.flags: BindingFlags

The type of the None singleton.

Added in version 2.26.

props.source: Object

The type of the None singleton.

Added in version 2.26.

props.source_property: str

The type of the None singleton.

Added in version 2.26.

props.target: Object

The type of the None singleton.

Added in version 2.26.

props.target_property: str

The type of the None singleton.

Added in version 2.26.