GObject.Binding

const GObject = imports.gi.GObject;

let binding = new GObject.Binding({
    flags: value,
    source: value,
    source_property: value,
    target: value,
    target_property: value,
});
  

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

|[<!-- language="C" --> 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 GObject.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.Object instances, so that if either property changes, the other is updated as well, for instance:

|[<!-- language="C" --> 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:

|[<!-- language="C" --> 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 GObject.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.Object::notify signal only if the value has effectively been changed. A binding is implemented using the GObject.Object::notify signal, so it is susceptible to all the various ways of blocking a signal emission, like GObject.signal_stop_emission or GObject.signal_handler_block.

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

Bindings for languages with garbage collection can use GObject.Binding.prototype.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.

GObject.Binding is available since GObject 2.26

Since 2.26