GObject.Binding¶
class — extends 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:
will cause the property named "property-b" of object2 to be updated
every time GObject.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:
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
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.
Methods¶
dup_source¶
Retrieves the Object instance used as the source of the binding.
A Binding can outlive the source Object as the binding does not hold a
strong reference to the source. If the source is destroyed before the
binding then this function will return None.
dup_target¶
Retrieves the Object instance used as the target of the binding.
A Binding can outlive the target Object as the binding does not hold a
strong reference to the target. If the target is destroyed before the
binding then this function will return None.
get_flags¶
Retrieves the flags passed when constructing the Binding.
get_source¶
:::warning Deprecated since 2.68 This API is deprecated. :::
Retrieves the Object instance used as the source of the binding.
A Binding can outlive the source Object as the binding does not hold a
strong reference to the source. If the source is destroyed before the
binding then this function will return None.
Use Binding.dup_source if the source or binding are used from different
threads as otherwise the pointer returned from this function might become
invalid if the source is finalized from another thread in the meantime.
get_source_property¶
Retrieves the name of the property of Binding:source used as the source
of the binding.
get_target¶
:::warning Deprecated since 2.68 This API is deprecated. :::
Retrieves the Object instance used as the target of the binding.
A Binding can outlive the target Object as the binding does not hold a
strong reference to the target. If the target is destroyed before the
binding then this function will return None.
Use Binding.dup_target if the target or binding are used from different
threads as otherwise the pointer returned from this function might become
invalid if the target is finalized from another thread in the meantime.
get_target_property¶
Retrieves the name of the property of Binding:target used as the target
of the 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 Binding.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
Object.bind_property and is owned by the binding.
Properties¶
flags¶
Flags to be used to control the Binding
source¶
The Object that should be used as the source of the binding
source_property¶
The name of the property of Binding:source that should be used
as the source of the binding.
This should be in [canonical form][classGObject.ParamSpec#parameter-names] to get the
best performance.
target¶
The Object that should be used as the target of the binding
target_property¶
The name of the property of Binding:target that should be used
as the target of the binding.
This should be in [canonical form][classGObject.ParamSpec#parameter-names] to get the
best performance.