class GObject::Binding

• GObject::Binding
• GObject::Object
• Reference
• Object

Overview

#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:

|[ 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:

|[ 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 #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

Defined in:

Constructors

• .new

  Initialize a new Binding.

• .new(*, flags : GObject::BindingFlags | Nil = nil, source : GObject::Object | Nil = nil, source_property : String | Nil = nil, target : GObject::Object | Nil = nil, target_property : String | Nil = nil)

Class Method Summary

• .g_type : UInt64

  Returns the type id (GType) registered in GLib type system.

Instance Method Summary

• #==(other : self)

  Returns true if this reference is the same as other.

• #dup_source : GObject::Object | Nil

  Retrieves the #GObject instance used as the source of the binding.

• #dup_target : GObject::Object | Nil

  Retrieves the #GObject instance used as the target of the binding.

• #flags : GObject::BindingFlags

  Retrieves the flags passed when constructing the #GBinding.

• #flags=(value : GObject::BindingFlags) : GObject::BindingFlags
• #hash(hasher)

  See Object#hash(hasher)

• #source : GObject::Object | Nil

  Retrieves the #GObject instance used as the source of the binding.

  DEPRECATED

• #source=(value : GObject::Object | Nil) : GObject::Object | Nil
• #source_property : String

  Retrieves the name of the property of #GBinding:source used as the source of the binding.

• #source_property=(value : String) : String
• #source_property=(value : Nil) : Nil

  Set #source_property property to nil.

• #source_property? : String | Nil

  Same as #source_property, but can return nil.

• #target : GObject::Object | Nil

  Retrieves the #GObject instance used as the target of the binding.

  DEPRECATED

• #target=(value : GObject::Object | Nil) : GObject::Object | Nil
• #target_property : String

  Retrieves the name of the property of #GBinding:target used as the target of the binding.

• #target_property=(value : String) : String
• #target_property=(value : Nil) : Nil

  Set #target_property property to nil.

• #target_property? : String | Nil

  Same as #target_property, but can return nil.

• #unbind : Nil

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

Constructor Detail

Class Method Detail

Instance Method Detail