class Gtk::Stack
Overview
Gtk::Stack
is a container which only shows one of its children
at a time.
In contrast to Gtk::Notebook
, Gtk::Stack
does not provide a means
for users to change the visible child. Instead, a separate widget
such as Gtk::StackSwitcher
or Gtk::StackSidebar
can
be used with Gtk::Stack
to provide this functionality.
Transitions between pages can be animated as slides or fades. This
can be controlled with Gtk::Stack#transition_type=
.
These animations respect the [property@Gtk.Settings:gtk-enable-animations]
setting.
Gtk::Stack
maintains a Gtk::StackPage
object for each added
child, which holds additional per-child properties. You
obtain the Gtk::StackPage
for a child with Gtk::Stack#page
and you can obtain a Gtk::SelectionModel
containing all the pages
with Gtk::Stack#pages
.
Gtk::Stack as Gtk::Buildable
To set child-specific properties in a .ui file, create Gtk::StackPage
objects explicitly, and set the child widget as a property on it:
WARNING ⚠️ The following code is in xml ⚠️
<object class="Gtk::Stack" id="stack">
<child>
<object class="Gtk::StackPage">
<property name="name">page1</property>
<property name="title">In the beginning…</property>
<property name="child">
<object class="Gtk::Label">
<property name="label">It was dark</property>
</object>
</property>
</object>
</child>
CSS nodes
Gtk::Stack
has a single CSS node named stack.
Accessibility
Gtk::Stack
uses the %GTK_ACCESSIBLE_ROLE_TAB_PANEL for the stack
pages, which are the accessible parent objects of the child widgets.
Included Modules
Defined in:
lib/gi-crystal/src/auto/gtk-4.0/stack.crlib/gtk4/src/bindings/gtk/stack.cr
Constructors
-
.new : self
Creates a new
Gtk::Stack
. - .new(*, accessible_role : Gtk::AccessibleRole? = nil, can_focus : Bool? = nil, can_target : Bool? = nil, css_classes : Enumerable(String)? = nil, css_name : String? = nil, cursor : Gdk::Cursor? = nil, focus_on_click : Bool? = nil, focusable : Bool? = nil, halign : Gtk::Align? = nil, has_default : Bool? = nil, has_focus : Bool? = nil, has_tooltip : Bool? = nil, height_request : Int32? = nil, hexpand : Bool? = nil, hexpand_set : Bool? = nil, hhomogeneous : Bool? = nil, interpolate_size : Bool? = nil, layout_manager : Gtk::LayoutManager? = nil, margin_bottom : Int32? = nil, margin_end : Int32? = nil, margin_start : Int32? = nil, margin_top : Int32? = nil, name : String? = nil, opacity : Float64? = nil, overflow : Gtk::Overflow? = nil, pages : Gtk::SelectionModel? = nil, parent : Gtk::Widget? = nil, receives_default : Bool? = nil, root : Gtk::Root? = nil, scale_factor : Int32? = nil, sensitive : Bool? = nil, tooltip_markup : String? = nil, tooltip_text : String? = nil, transition_duration : UInt32? = nil, transition_running : Bool? = nil, transition_type : Gtk::StackTransitionType? = nil, valign : Gtk::Align? = nil, vexpand : Bool? = nil, vexpand_set : Bool? = nil, vhomogeneous : Bool? = nil, visible : Bool? = nil, visible_child : Gtk::Widget? = nil, visible_child_name : String? = nil, width_request : Int32? = nil)
Class Method Summary
-
.g_type : UInt64
Returns the type id (GType) registered in GLib type system.
Instance Method Summary
-
#add_child(child : Gtk::Widget) : Gtk::StackPage
Adds a child to @stack.
-
#add_named(child : Gtk::Widget, name : String?) : Gtk::StackPage
Adds a child to @stack.
-
#add_titled(child : Gtk::Widget, name : String?, title : String) : Gtk::StackPage
Adds a child to @stack.
-
#child_by_name(name : String) : Gtk::Widget?
Finds the child with the name given as the argument.
-
#hhomogeneous : Bool
Gets whether @stack is horizontally homogeneous.
-
#hhomogeneous=(hhomogeneous : Bool) : Nil
Sets the
Gtk::Stack
to be horizontally homogeneous or not. - #hhomogeneous? : Bool
-
#interpolate_size : Bool
Returns whether the
Gtk::Stack
is set up to interpolate between the sizes of children on page switch. -
#interpolate_size=(interpolate_size : Bool) : Nil
Sets whether or not @stack will interpolate its size when changing the visible child.
- #interpolate_size? : Bool
-
#page(child : Gtk::Widget) : Gtk::StackPage
Returns the
Gtk::StackPage
object for @child. -
#pages : Gtk::SelectionModel
Returns a
GListModel
that contains the pages of the stack. -
#remove(child : Gtk::Widget) : Nil
Removes a child widget from @stack.
-
#set_visible_child_full(name : String, transition : Gtk::StackTransitionType) : Nil
Makes the child with the given name visible.
-
#transition_duration : UInt32
Returns the amount of time (in milliseconds) that transitions between pages in @stack will take.
-
#transition_duration=(duration : UInt32) : Nil
Sets the duration that transitions between pages in @stack will take.
-
#transition_running : Bool
Returns whether the @stack is currently in a transition from one page to another.
- #transition_running? : Bool
-
#transition_type : Gtk::StackTransitionType
Gets the type of animation that will be used for transitions between pages in @stack.
-
#transition_type=(transition : Gtk::StackTransitionType) : Nil
Sets the type of animation that will be used for transitions between pages in @stack.
-
#vhomogeneous : Bool
Gets whether @stack is vertically homogeneous.
-
#vhomogeneous=(vhomogeneous : Bool) : Nil
Sets the
Gtk::Stack
to be vertically homogeneous or not. - #vhomogeneous? : Bool
-
#visible_child : Gtk::Widget?
Gets the currently visible child of @stack.
-
#visible_child=(child : Gtk::Widget) : Nil
Makes @child the visible child of @stack.
- #visible_child=(value : Gtk::Widget?) : Gtk::Widget?
-
#visible_child_name : String?
Returns the name of the currently visible child of @stack.
-
#visible_child_name=(name : String) : Nil
Makes the child with the given name visible.
Instance methods inherited from module Gtk::ConstraintTarget
to_unsafe
to_unsafe
Class methods inherited from module Gtk::ConstraintTarget
g_type : UInt64
g_type
Instance methods inherited from module Gtk::Buildable
buildable_id : String?
buildable_id,
to_unsafe
to_unsafe
Class methods inherited from module Gtk::Buildable
g_type : UInt64
g_type
Instance methods inherited from module Gtk::Accessible
accessible_role : Gtk::AccessibleRole
accessible_role,
accessible_role=(value : Gtk::AccessibleRole) : Gtk::AccessibleRole
accessible_role=,
reset_property(property : Gtk::AccessibleProperty) : Nil
reset_property,
reset_relation(relation : Gtk::AccessibleRelation) : Nil
reset_relation,
reset_state(state : Gtk::AccessibleState) : Nil
reset_state,
to_unsafe
to_unsafe,
update_property(properties : Enumerable(Gtk::AccessibleProperty), values : Enumerable(_)) : Nil
update_property,
update_relation(relations : Enumerable(Gtk::AccessibleRelation), values : Enumerable(_)) : Nil
update_relation,
update_state(states : Enumerable(Gtk::AccessibleState), values : Enumerable(_)) : Nil
update_state
Class methods inherited from module Gtk::Accessible
g_type : UInt64
g_type
Instance methods inherited from class Gtk::Widget
action_set_enabled(action_name : String, enabled : Bool) : Nil
action_set_enabled,
activate : Bool
activate,
activate_action(name : String, args : _?) : Bool
activate_action,
activate_default : Nil
activate_default,
add_controller(controller : Gtk::EventController) : Nil
add_controller,
add_css_class(css_class : String) : Nil
add_css_class,
add_mnemonic_label(label : Gtk::Widget) : Nil
add_mnemonic_label,
add_tick_callback(callback : Gtk::TickCallback) : UInt32
add_tick_callback,
allocate(width : Int32, height : Int32, baseline : Int32, transform : Gsk::Transform?) : Nil
allocate,
allocated_baseline : Int32
allocated_baseline,
allocated_height : Int32
allocated_height,
allocated_width : Int32
allocated_width,
allocation : Gdk::Rectangle
allocation,
ancestor(widget_type : UInt64) : Gtk::Widget?
ancestor,
can_focus : Bool
can_focus,
can_focus=(can_focus : Bool) : Nil
can_focus=,
can_focus? : Bool
can_focus?,
can_target : Bool
can_target,
can_target=(can_target : Bool) : Nil
can_target=,
can_target? : Bool
can_target?,
child_focus(direction : Gtk::DirectionType) : Bool
child_focus,
child_visible : Bool
child_visible,
child_visible=(child_visible : Bool) : Nil
child_visible=,
clipboard : Gdk::Clipboard
clipboard,
compute_bounds(target : Gtk::Widget) : Graphene::Rect
compute_bounds,
compute_expand(orientation : Gtk::Orientation) : Bool
compute_expand,
compute_point(target : Gtk::Widget, point : Graphene::Point) : Graphene::Point
compute_point,
compute_transform(target : Gtk::Widget) : Graphene::Matrix
compute_transform,
contains(x : Float64, y : Float64) : Bool
contains,
create_pango_context : Pango::Context
create_pango_context,
create_pango_layout(text : String?) : Pango::Layout
create_pango_layout,
css_classes : Enumerable(String)
css_classes,
css_classes=(classes : Enumerable(String)) : Nil
css_classes=,
css_name : String
css_name,
css_name=(value : String) : String
css_name=,
cursor : Gdk::Cursor?
cursor,
cursor=(cursor : Gdk::Cursor?) : Nil
cursor=,
cursor_from_name=(name : String?) : Nil
cursor_from_name=,
destroy_signal
destroy_signal,
direction : Gtk::TextDirection
direction,
direction=(dir : Gtk::TextDirection) : Nil
direction=,
direction_changed_signal
direction_changed_signal,
display : Gdk::Display
display,
dispose_template(widget_type : UInt64) : Nil
dispose_template,
drag_check_threshold(start_x : Int32, start_y : Int32, current_x : Int32, current_y : Int32) : Bool
drag_check_threshold,
error_bell : Nil
error_bell,
first_child : Gtk::Widget?
first_child,
focus_child : Gtk::Widget?
focus_child,
focus_child=(child : Gtk::Widget?) : Nil
focus_child=,
focus_on_click : Bool
focus_on_click,
focus_on_click=(focus_on_click : Bool) : Nil
focus_on_click=,
focus_on_click? : Bool
focus_on_click?,
focusable : Bool
focusable,
focusable=(focusable : Bool) : Nil
focusable=,
focusable? : Bool
focusable?,
font_map : Pango::FontMap?
font_map,
font_map=(font_map : Pango::FontMap?) : Nil
font_map=,
font_options : Cairo::FontOptions?
font_options,
font_options=(options : Cairo::FontOptions?) : Nil
font_options=,
frame_clock : Gdk::FrameClock?
frame_clock,
grab_focus : Bool
grab_focus,
halign : Gtk::Align
halign,
halign=(align : Gtk::Align) : Nil
halign=,
has_css_class(css_class : String) : Bool
has_css_class,
has_default : Bool
has_default,
has_default? : Bool
has_default?,
has_focus : Bool
has_focus,
has_focus? : Bool
has_focus?,
has_tooltip : Bool
has_tooltip,
has_tooltip=(has_tooltip : Bool) : Nil
has_tooltip=,
has_tooltip? : Bool
has_tooltip?,
has_visible_focus : Bool
has_visible_focus,
height : Int32
height,
height_request : Int32
height_request,
height_request=(value : Int32) : Int32
height_request=,
hexpand : Bool
hexpand,
hexpand=(expand : Bool) : Nil
hexpand=,
hexpand? : Bool
hexpand?,
hexpand_set : Bool
hexpand_set,
hexpand_set=(set : Bool) : Nil
hexpand_set=,
hexpand_set? : Bool
hexpand_set?,
hide : Nil
hide,
hide_signal
hide_signal,
in_destruction : Bool
in_destruction,
init_template : Nil
init_template,
insert_action_group(name : String, group : Gio::ActionGroup?) : Nil
insert_action_group,
insert_after(parent : Gtk::Widget, previous_sibling : Gtk::Widget?) : Nil
insert_after,
insert_before(parent : Gtk::Widget, next_sibling : Gtk::Widget?) : Nil
insert_before,
is_ancestor(ancestor : Gtk::Widget) : Bool
is_ancestor,
is_drawable : Bool
is_drawable,
is_focus : Bool
is_focus,
is_sensitive : Bool
is_sensitive,
is_visible : Bool
is_visible,
keynav_failed(direction : Gtk::DirectionType) : Bool
keynav_failed,
keynav_failed_signal
keynav_failed_signal,
last_child : Gtk::Widget?
last_child,
layout_manager : Gtk::LayoutManager?
layout_manager,
layout_manager=(layout_manager : Gtk::LayoutManager?) : Nil
layout_manager=,
list_mnemonic_labels : GLib::List
list_mnemonic_labels,
map : Nil
map,
map_signal
map_signal,
mapped : Bool
mapped,
margin_bottom : Int32
margin_bottom,
margin_bottom=(margin : Int32) : Nil
margin_bottom=,
margin_end : Int32
margin_end,
margin_end=(margin : Int32) : Nil
margin_end=,
margin_start : Int32
margin_start,
margin_start=(margin : Int32) : Nil
margin_start=,
margin_top : Int32
margin_top,
margin_top=(margin : Int32) : Nil
margin_top=,
measure(orientation : Gtk::Orientation, for_size : Int32) : Nil
measure,
mnemonic_activate(group_cycling : Bool) : Bool
mnemonic_activate,
mnemonic_activate_signal
mnemonic_activate_signal,
move_focus_signal
move_focus_signal,
name : String
name,
name=(name : String) : Nil
name=,
native : Gtk::Native?
native,
next_sibling : Gtk::Widget?
next_sibling,
observe_children : Gio::ListModel
observe_children,
observe_controllers : Gio::ListModel
observe_controllers,
opacity : Float64
opacity,
opacity=(opacity : Float64) : Nil
opacity=,
overflow : Gtk::Overflow
overflow,
overflow=(overflow : Gtk::Overflow) : Nil
overflow=,
pango_context : Pango::Context
pango_context,
parent : Gtk::Widget?
parent,
parent=(parent : Gtk::Widget) : Nil
parent=,
pick(x : Float64, y : Float64, flags : Gtk::PickFlags) : Gtk::Widget?
pick,
preferred_size : Gtk::Requisition
preferred_size,
prev_sibling : Gtk::Widget?
prev_sibling,
primary_clipboard : Gdk::Clipboard
primary_clipboard,
query_tooltip_signal
query_tooltip_signal,
queue_allocate : Nil
queue_allocate,
queue_draw : Nil
queue_draw,
queue_resize : Nil
queue_resize,
realize : Nil
realize,
realize_signal
realize_signal,
realized : Bool
realized,
receives_default : Bool
receives_default,
receives_default=(receives_default : Bool) : Nil
receives_default=,
receives_default? : Bool
receives_default?,
remove_controller(controller : Gtk::EventController) : Nil
remove_controller,
remove_css_class(css_class : String) : Nil
remove_css_class,
remove_mnemonic_label(label : Gtk::Widget) : Nil
remove_mnemonic_label,
remove_tick_callback(id : UInt32) : Nil
remove_tick_callback,
request_mode : Gtk::SizeRequestMode
request_mode,
root : Gtk::Root?
root,
scale_factor : Int32
scale_factor,
sensitive : Bool
sensitive,
sensitive=(sensitive : Bool) : Nil
sensitive=,
sensitive? : Bool
sensitive?,
set_size_request(width : Int32, height : Int32) : Nil
set_size_request,
set_state_flags(flags : Gtk::StateFlags, clear : Bool) : Nil
set_state_flags,
settings : Gtk::Settings
settings,
should_layout : Bool
should_layout,
show : Nil
show,
show_signal
show_signal,
size(orientation : Gtk::Orientation) : Int32
size,
size_allocate(allocation : Gdk::Rectangle, baseline : Int32) : Nil
size_allocate,
size_request : Nil
size_request,
snapshot_child(child : Gtk::Widget, snapshot : Gtk::Snapshot) : Nil
snapshot_child,
state_flags : Gtk::StateFlags
state_flags,
state_flags_changed_signal
state_flags_changed_signal,
style_context : Gtk::StyleContext
style_context,
tooltip_markup : String?
tooltip_markup,
tooltip_markup=(value : String) : Stringtooltip_markup=(markup : String?) : Nil tooltip_markup=, tooltip_text : String? tooltip_text, tooltip_text=(value : String) : String
tooltip_text=(text : String?) : Nil tooltip_text=, translate_coordinates(dest_widget : Gtk::Widget, src_x : Float64, src_y : Float64) : Bool translate_coordinates, trigger_tooltip_query : Nil trigger_tooltip_query, unmap : Nil unmap, unmap_signal unmap_signal, unparent : Nil unparent, unrealize : Nil unrealize, unrealize_signal unrealize_signal, unset_state_flags(flags : Gtk::StateFlags) : Nil unset_state_flags, valign : Gtk::Align valign, valign=(align : Gtk::Align) : Nil valign=, vexpand : Bool vexpand, vexpand=(expand : Bool) : Nil vexpand=, vexpand? : Bool vexpand?, vexpand_set : Bool vexpand_set, vexpand_set=(set : Bool) : Nil vexpand_set=, vexpand_set? : Bool vexpand_set?, visible : Bool visible, visible=(visible : Bool) : Nil visible=, visible? : Bool visible?, width : Int32 width, width_request : Int32 width_request, width_request=(value : Int32) : Int32 width_request=
Constructor methods inherited from class Gtk::Widget
newnew(*, accessible_role : Gtk::AccessibleRole? = nil, can_focus : Bool? = nil, can_target : Bool? = nil, css_classes : Enumerable(String)? = nil, css_name : String? = nil, cursor : Gdk::Cursor? = nil, focus_on_click : Bool? = nil, focusable : Bool? = nil, halign : Gtk::Align? = nil, has_default : Bool? = nil, has_focus : Bool? = nil, has_tooltip : Bool? = nil, height_request : Int32? = nil, hexpand : Bool? = nil, hexpand_set : Bool? = nil, layout_manager : Gtk::LayoutManager? = nil, margin_bottom : Int32? = nil, margin_end : Int32? = nil, margin_start : Int32? = nil, margin_top : Int32? = nil, name : String? = nil, opacity : Float64? = nil, overflow : Gtk::Overflow? = nil, parent : Gtk::Widget? = nil, receives_default : Bool? = nil, root : Gtk::Root? = nil, scale_factor : Int32? = nil, sensitive : Bool? = nil, tooltip_markup : String? = nil, tooltip_text : String? = nil, valign : Gtk::Align? = nil, vexpand : Bool? = nil, vexpand_set : Bool? = nil, visible : Bool? = nil, width_request : Int32? = nil) new
Class methods inherited from class Gtk::Widget
default_direction : Gtk::TextDirection
default_direction,
default_direction=(dir : Gtk::TextDirection) : Nil
default_direction=,
g_type : UInt64
g_type
Instance methods inherited from module Gtk::ConstraintTarget
to_unsafe
to_unsafe
Class methods inherited from module Gtk::ConstraintTarget
g_type : UInt64
g_type
Instance methods inherited from module Gtk::Buildable
buildable_id : String?
buildable_id,
to_unsafe
to_unsafe
Class methods inherited from module Gtk::Buildable
g_type : UInt64
g_type
Instance methods inherited from module Gtk::Accessible
accessible_role : Gtk::AccessibleRole
accessible_role,
accessible_role=(value : Gtk::AccessibleRole) : Gtk::AccessibleRole
accessible_role=,
reset_property(property : Gtk::AccessibleProperty) : Nil
reset_property,
reset_relation(relation : Gtk::AccessibleRelation) : Nil
reset_relation,
reset_state(state : Gtk::AccessibleState) : Nil
reset_state,
to_unsafe
to_unsafe,
update_property(properties : Enumerable(Gtk::AccessibleProperty), values : Enumerable(_)) : Nil
update_property,
update_relation(relations : Enumerable(Gtk::AccessibleRelation), values : Enumerable(_)) : Nil
update_relation,
update_state(states : Enumerable(Gtk::AccessibleState), values : Enumerable(_)) : Nil
update_state
Class methods inherited from module Gtk::Accessible
g_type : UInt64
g_type
Constructor methods inherited from class GObject::InitiallyUnowned
new
new
Class methods inherited from class GObject::InitiallyUnowned
g_type : UInt64
g_type
Instance methods inherited from class GObject::Object
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)?
data,
finalize
finalize,
freeze_notify : Nil
freeze_notify,
getv(names : Enumerable(String), values : Enumerable(_)) : Nil
getv,
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)?
qdata,
ref_count : UInt32
ref_count,
run_dispose : Nil
run_dispose,
set_data(key : String, data : Pointer(Void)?) : Nil
set_data,
set_property(property_name : String, value : _) : Nil
set_property,
steal_data(key : String) : Pointer(Void)?
steal_data,
steal_qdata(quark : UInt32) : Pointer(Void)?
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,
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
compat_control(what : UInt64, data : Pointer(Void)?) : 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
Constructor Detail
Class Method Detail
Instance Method Detail
Adds a child to @stack.
The child is identified by the @name.
Adds a child to @stack.
The child is identified by the @name. The @title
will be used by Gtk::StackSwitcher
to represent
@child in a tab bar, so it should be short.
Finds the child with the name given as the argument.
Returns nil
if there is no child with this name.
Sets the Gtk::Stack
to be horizontally homogeneous or not.
If it is homogeneous, the Gtk::Stack
will request the same
width for all its children. If it isn't, the stack
may change width when a different child becomes visible.
Returns whether the Gtk::Stack
is set up to interpolate between
the sizes of children on page switch.
Sets whether or not @stack will interpolate its size when changing the visible child.
If the [property@Gtk.Stack:interpolate-size] property is set
to true
, @stack will interpolate its size between the current
one and the one it'll take after changing the visible child,
according to the set transition duration.
Returns a GListModel
that contains the pages of the stack.
This can be used to keep an up-to-date view. The model also
implements Gtk::SelectionModel
and can be used to track
and modify the visible page.
Makes the child with the given name visible.
Note that the child widget has to be visible itself
(see Gtk::Widget#show
) in order to become the visible
child of @stack.
Returns the amount of time (in milliseconds) that transitions between pages in @stack will take.
Sets the duration that transitions between pages in @stack will take.
Returns whether the @stack is currently in a transition from one page to another.
Gets the type of animation that will be used for transitions between pages in @stack.
Sets the type of animation that will be used for transitions between pages in @stack.
Available types include various kinds of fades and slides.
The transition type can be changed without problems at runtime, so it is possible to change the animation based on the page that is about to become current.
Sets the Gtk::Stack
to be vertically homogeneous or not.
If it is homogeneous, the Gtk::Stack
will request the same
height for all its children. If it isn't, the stack
may change height when a different child becomes visible.
Gets the currently visible child of @stack.
Returns nil
if there are no visible children.
Makes @child the visible child of @stack.
If @child is different from the currently visible child, the transition between the two will be animated with the current transition type of @stack.
Note that the @child widget has to be visible itself
(see Gtk::Widget#show
) in order to become the visible
child of @stack.
Returns the name of the currently visible child of @stack.
Returns nil
if there is no visible child.
Makes the child with the given name visible.
If @child is different from the currently visible child, the transition between the two will be animated with the current transition type of @stack.
Note that the child widget has to be visible itself
(see Gtk::Widget#show
) in order to become the visible
child of @stack.