AtkValue

AtkValue — The ATK interface implemented by valuators and components which display or select a value from a bounded range of values.

Signals

void value-changed Run Last

Types and Values

Object Hierarchy

    GInterface
    ╰── AtkValue

Known Implementations

AtkValue is implemented by AtkNoOpObject.

Description

AtkValue should be implemented for components which either display a value from a bounded range, or which allow the user to specify a value from a bounded range, or both. For instance, most sliders and range controls, as well as dials, should have AtkObject representations which implement AtkValue on the component's behalf. AtKValues may be read-only, in which case attempts to alter the value return would fail.

On the subject of current value text

In addition to providing the current value, implementors can optionally provide an end-user-consumable textual description associated with this value. This description should be included when the numeric value fails to convey the full, on-screen representation seen by users.

Example 1. Password strength

A password strength meter whose value changes as the user types their new password. Red is used for values less than 4.0, yellow for values between 4.0 and 7.0, and green for values greater than 7.0. In this instance, value text should be provided by the implementor. Appropriate value text would be "weak", "acceptable," and "strong" respectively.


A level bar whose value changes to reflect the battery charge. The color remains the same regardless of the charge and there is no on-screen text reflecting the fullness of the battery. In this case, because the position within the bar is the only indication the user has of the current charge, value text should not be provided by the implementor.

Implementor Notes

Implementors should bear in mind that assistive technologies will likely prefer the value text provided over the numeric value when presenting a widget's value. As a result, strings not intended for end users should not be exposed in the value text, and strings which are exposed should be localized. In the case of widgets which display value text on screen, for instance through a separate label in close proximity to the value-displaying widget, it is still expected that implementors will expose the value text using the above API.

AtkValue should NOT be implemented for widgets whose displayed value is not reflective of a meaningful amount. For instance, a progress pulse indicator whose value alternates between 0.0 and 1.0 to indicate that some process is still taking place should not implement AtkValue because the current value does not reflect progress towards completion.

On the subject of ranges

In addition to providing the minimum and maximum values, implementors can optionally provide details about subranges associated with the widget. These details should be provided by the implementor when both of the following are communicated visually to the end user:

  • The existence of distinct ranges such as "weak", "acceptable", and "strong" indicated by color, bar tick marks, and/or on-screen text.
  • Where the current value stands within a given subrange, for instance illustrating progression from very "weak" towards nearly "acceptable" through changes in shade and/or position on the bar within the "weak" subrange.

If both of the above do not apply to the widget, it should be sufficient to expose the numeric value, along with the value text if appropriate, to make the widget accessible.

Implementor Notes

If providing subrange details is deemed necessary, all possible values of the widget are expected to fall within one of the subranges defined by the implementor.

On the subject of localization of end-user-consumable text values

Because value text and subrange descriptors are human-consumable, implementors are expected to provide localized strings which can be directly presented to end users via their assistive technology. In order to simplify this for implementors, implementors can use atk_value_type_get_localized_name() with the following already-localized constants for commonly-needed values can be used:

  • ATK_VALUE_VERY_WEAK
  • ATK_VALUE_WEAK
  • ATK_VALUE_ACCEPTABLE
  • ATK_VALUE_STRONG
  • ATK_VALUE_VERY_STRONG
  • ATK_VALUE_VERY_LOW
  • ATK_VALUE_LOW
  • ATK_VALUE_MEDIUM
  • ATK_VALUE_HIGH
  • ATK_VALUE_VERY_HIGH
  • ATK_VALUE_VERY_BAD
  • ATK_VALUE_BAD
  • ATK_VALUE_GOOD
  • ATK_VALUE_VERY_GOOD
  • ATK_VALUE_BEST
  • ATK_VALUE_SUBSUBOPTIMAL
  • ATK_VALUE_SUBOPTIMAL
  • ATK_VALUE_OPTIMAL

Proposals for additional constants, along with their use cases, should be submitted to the GNOME Accessibility Team.

On the subject of changes

Note that if there is a textual description associated with the new numeric value, that description should be included regardless of whether or not it has also changed.

Functions

atk_value_get_current_value ()

void
atk_value_get_current_value (AtkValue *obj,
                             GValue *value);

atk_value_get_current_value is deprecated and should not be used in newly-written code.

Since 2.12. Use atk_value_get_value_and_text() instead.

Gets the value of this object.

Parameters

obj

a GObject instance that implements AtkValueIface

 

value

a GValue representing the current accessible value.

[out]

atk_value_get_maximum_value ()

void
atk_value_get_maximum_value (AtkValue *obj,
                             GValue *value);

atk_value_get_maximum_value is deprecated and should not be used in newly-written code.

Since 2.12. Use atk_value_get_range() instead.

Gets the maximum value of this object.

Parameters

obj

a GObject instance that implements AtkValueIface

 

value

a GValue representing the maximum accessible value.

[out]

atk_value_get_minimum_value ()

void
atk_value_get_minimum_value (AtkValue *obj,
                             GValue *value);

atk_value_get_minimum_value is deprecated and should not be used in newly-written code.

Since 2.12. Use atk_value_get_range() instead.

Gets the minimum value of this object.

Parameters

obj

a GObject instance that implements AtkValueIface

 

value

a GValue representing the minimum accessible value.

[out]

atk_value_set_current_value ()

gboolean
atk_value_set_current_value (AtkValue *obj,
                             const GValue *value);

atk_value_set_current_value is deprecated and should not be used in newly-written code.

Since 2.12. Use atk_value_set_value() instead.

Sets the value of this object.

Parameters

obj

a GObject instance that implements AtkValueIface

 

value

a GValue which is the desired new accessible value.

 

Returns

TRUE if new value is successfully set, FALSE otherwise.


atk_value_get_minimum_increment ()

void
atk_value_get_minimum_increment (AtkValue *obj,
                                 GValue *value);

atk_value_get_minimum_increment is deprecated and should not be used in newly-written code.

Since 2.12. Use atk_value_get_increment() instead.

Gets the minimum increment by which the value of this object may be changed. If zero, the minimum increment is undefined, which may mean that it is limited only by the floating point precision of the platform.

Parameters

obj

a GObject instance that implements AtkValueIface

 

value

a GValue representing the minimum increment by which the accessible value may be changed.

[out]

Since: 1.12


atk_value_get_value_and_text ()

void
atk_value_get_value_and_text (AtkValue *obj,
                              gdouble *value,
                              gchar **text);

Gets the current value and the human readable text alternative of obj . text is a newly created string, that must be freed by the caller. Can be NULL if no descriptor is available.

Parameters

obj

a GObject instance that implements AtkValueIface

 

value

address of gdouble to put the current value of obj .

[out]

text

address of gchar to put the human readable text alternative for value .

[out][allow-none]

Since: 2.12


atk_value_get_range ()

AtkRange *
atk_value_get_range (AtkValue *obj);

Gets the range of this object.

Parameters

obj

a GObject instance that implements AtkValueIface

 

Returns

a newly allocated AtkRange that represents the minimum, maximum and descriptor (if available) of obj . NULL if that range is not defined.

[nullable][transfer full]

Since: 2.12


atk_value_get_increment ()

gdouble
atk_value_get_increment (AtkValue *obj);

Gets the minimum increment by which the value of this object may be changed. If zero, the minimum increment is undefined, which may mean that it is limited only by the floating point precision of the platform.

Parameters

obj

a GObject instance that implements AtkValueIface

 

Returns

the minimum increment by which the value of this object may be changed. zero if undefined.

Since: 2.12


atk_value_get_sub_ranges ()

GSList *
atk_value_get_sub_ranges (AtkValue *obj);

Gets the list of subranges defined for this object. See AtkValue introduction for examples of subranges and when to expose them.

Parameters

obj

a GObject instance that implements AtkValueIface

 

Returns

an GSList of AtkRange which each of the subranges defined for this object. Free the returns list with g_slist_free().

[element-type AtkRange][transfer full]

Since: 2.12


atk_value_set_value ()

void
atk_value_set_value (AtkValue *obj,
                     const gdouble new_value);

Sets the value of this object.

This method is intended to provide a way to change the value of the object. In any case, it is possible that the value can't be modified (ie: a read-only component). If the value changes due this call, it is possible that the text could change, and will trigger an “value-changed” signal emission.

Note for implementors: the deprecated atk_value_set_current_value() method returned TRUE or FALSE depending if the value was assigned or not. In the practice several implementors were not able to decide it, and returned TRUE in any case. For that reason it is not required anymore to return if the value was properly assigned or not.

Parameters

obj

a GObject instance that implements AtkValueIface

 

new_value

a double which is the desired new accessible value.

 

Since: 2.12

Types and Values

AtkValue

typedef struct _AtkValue AtkValue;

Signal Details

The “value-changed” signal

void
user_function (AtkValue *atkvalue,
               gdouble   value,
               gchar    *text,
               gpointer  user_data)

The 'value-changed' signal is emitted when the current value that represent the object changes. value is the numerical representation of this new value. text is the human readable text alternative of value , and can be NULL if it is not available. Note that if there is a textual description associated with the new numeric value, that description should be included regardless of whether or not it has also changed.

Example: a password meter whose value changes as the user types their new password. Appropiate value text would be "weak", "acceptable" and "strong".

Parameters

atkvalue

the object on which the signal was emitted.

 

value

the new value in a numerical form.

 

text

human readable text alternative (also called description) of this object. NULL if not available.

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last

Since: 2.12