class GObject::Binding

Overview

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:

WARNING ⚠️ The following code is in 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::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:

WARNING ⚠️ The following code is in 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:

WARNING ⚠️ The following code is in 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 #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 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 instances it refers to are finalized, or when the #GBinding instance loses its last reference.

Bindings for languages with garbage collection can use GObject::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.

Defined in:

lib/gi-crystal/src/auto/g_object-2.0/binding.cr

Constructors

Class Method Summary

Instance Method Summary

Instance methods inherited from class GObject::Object

==(other : self) ==, bind_property(source_property : String, target : GObject::Object, target_property : String, flags : GObject::BindingFlags) : GObject::Binding bind_property, bind_property_full(source_property : String, target : GObject::Object, target_property : String, flags : GObject::BindingFlags, transform_to : GObject::Closure, transform_from : GObject::Closure) : GObject::Binding bind_property_full, data(key : String) : Pointer(Void) | Nil data, finalize finalize, freeze_notify : Nil freeze_notify, getv(names : Enumerable(String), values : Enumerable(_)) : Nil getv, hash(hasher) hash, notify(property_name : String) : Nil notify, notify_by_pspec(pspec : GObject::ParamSpec) : Nil notify_by_pspec, notify_signal notify_signal, property(property_name : String, value : _) : Nil property, qdata(quark : UInt32) : Pointer(Void) | Nil qdata, ref_count : UInt32 ref_count, run_dispose : Nil run_dispose, set_data(key : String, data : Pointer(Void) | Nil) : Nil set_data, set_property(property_name : String, value : _) : Nil set_property, steal_data(key : String) : Pointer(Void) | Nil steal_data, steal_qdata(quark : UInt32) : Pointer(Void) | Nil steal_qdata, thaw_notify : Nil thaw_notify, to_unsafe : Pointer(Void) to_unsafe, watch_closure(closure : GObject::Closure) : Nil watch_closure

Constructor methods inherited from class GObject::Object

cast(obj : GObject::Object) : self cast, new(pointer : Pointer(Void), transfer : GICrystal::Transfer)
new new, newv(object_type : UInt64, parameters : Enumerable(GObject::Parameter)) : self newv

Class methods inherited from class GObject::Object

cast?(obj : GObject::Object) : self | Nil cast?, compat_control(what : UInt64, data : Pointer(Void) | Nil) : UInt64 compat_control, g_type : UInt64 g_type, interface_find_property(g_iface : GObject::TypeInterface, property_name : String) : GObject::ParamSpec interface_find_property, interface_list_properties(g_iface : GObject::TypeInterface) : Enumerable(GObject::ParamSpec) interface_list_properties

Macros inherited from class GObject::Object

previous_vfunc(*args) previous_vfunc, previous_vfunc!(*args) previous_vfunc!, signal(signature) signal

Constructor Detail

def self.new #

Initialize a new Binding.


def self.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 Detail

def self.g_type : UInt64 #

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


Instance Method Detail

def ==(other : self) #
Description copied from class Reference

Returns true if this reference is the same as other. Invokes same?.


def dup_source : GObject::Object | Nil #

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

A #GBinding can outlive the source #GObject 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 nil.


def dup_target : GObject::Object | Nil #

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

A #GBinding can outlive the target #GObject 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 nil.


def flags : GObject::BindingFlags #

Retrieves the flags passed when constructing the #GBinding.


def flags=(value : GObject::BindingFlags) : GObject::BindingFlags #

def hash(hasher) #
Description copied from class Reference

See Object#hash(hasher)


def source : GObject::Object | Nil #

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

A #GBinding can outlive the source #GObject 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 nil.

Use g_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.

DEPRECATED


def source=(value : GObject::Object | Nil) : GObject::Object | Nil #

def source_property : String #

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


def source_property=(value : String) : String #

def source_property=(value : Nil) : Nil #

Set #source_property property to nil.


def source_property? : String | Nil #

Same as #source_property, but can return nil.


def target : GObject::Object | Nil #

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

A #GBinding can outlive the target #GObject 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 nil.

Use g_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.

DEPRECATED


def target=(value : GObject::Object | Nil) : GObject::Object | Nil #

def target_property : String #

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


def target_property=(value : String) : String #

def target_property=(value : Nil) : Nil #

Set #target_property property to nil.


def target_property? : String | Nil #

Same as #target_property, but can return nil.


def unbind : Nil #

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 #GBinding instance after calling g_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 g_object_bind_property() and is owned by the binding.