GI.Atk.Interfaces.Value

Value 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 Object representations which implement Value on the component's behalf. AtKValues may be read-only, in which case attempts to alter the value return would fail.

<refsect1 id="current-value-text"> <title>On the subject of current value text</title> <para> 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. </para>

<example> <title>Password strength</title> 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. </example>

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.

<refsect2 id="implementor-notes"> <title>Implementor Notes</title> <para> 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. </para>

<para> Value 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 Value because the current value does not reflect progress towards completion. </para> </refsect2> </refsect1>

<refsect1 id="ranges"> <title>On the subject of ranges</title> <para> 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: </para> <itemizedlist> <listitem>The existence of distinct ranges such as "weak", "acceptable", and "strong" indicated by color, bar tick marks, and/or on-screen text.</listitem> <listitem>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.</listitem> </itemizedlist> <para> 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. </para>

<refsect2 id="ranges-implementor-notes"> <title>Implementor Notes</title> <para> 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. </para> </refsect2> </refsect1>

<refsect1 id="localization"> <title>On the subject of localization of end-user-consumable text values</title> <para> 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 valueTypeGetLocalizedName with the following already-localized constants for commonly-needed values can be used: </para>

<itemizedlist> <listitem>ATK_VALUE_VERY_WEAK</listitem> <listitem>ATK_VALUE_WEAK</listitem> <listitem>ATK_VALUE_ACCEPTABLE</listitem> <listitem>ATK_VALUE_STRONG</listitem> <listitem>ATK_VALUE_VERY_STRONG</listitem> <listitem>ATK_VALUE_VERY_LOW</listitem> <listitem>ATK_VALUE_LOW</listitem> <listitem>ATK_VALUE_MEDIUM</listitem> <listitem>ATK_VALUE_HIGH</listitem> <listitem>ATK_VALUE_VERY_HIGH</listitem> <listitem>ATK_VALUE_VERY_BAD</listitem> <listitem>ATK_VALUE_BAD</listitem> <listitem>ATK_VALUE_GOOD</listitem> <listitem>ATK_VALUE_VERY_GOOD</listitem> <listitem>ATK_VALUE_BEST</listitem> <listitem>ATK_VALUE_SUBSUBOPTIMAL</listitem> <listitem>ATK_VALUE_SUBOPTIMAL</listitem> <listitem>ATK_VALUE_OPTIMAL</listitem> </itemizedlist> <para> Proposals for additional constants, along with their use cases, should be submitted to the GNOME Accessibility Team. </para> </refsect1>

<refsect1 id="changes"> <title>On the subject of changes</title> <para> 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. </para> </refsect1>

Exported types

newtype Value

Memory-managed wrapper type.

Constructors

Value (ManagedPtr Value)

Instances

GObject Value

Defined in GI.Atk.Interfaces.Value

Methods

gobjectType :: Value -> IO GType

IsObject Value

Defined in GI.Atk.Interfaces.Value

IsValue Value

Defined in GI.Atk.Interfaces.Value

noValue :: Maybe Value

A convenience alias for Nothing :: Maybe Value.

class GObject o => IsValue o

Type class for types which can be safely cast to Value, for instance with toValue.

Instances

(GObject a, (UnknownAncestorError Value a :: Constraint)) => IsValue a

Defined in GI.Atk.Interfaces.Value

IsValue Value

Defined in GI.Atk.Interfaces.Value

IsValue NoOpObject

Defined in GI.Atk.Objects.NoOpObject

toValue :: (MonadIO m, IsValue o) => o -> m Value

Cast to Value, for types for which this is known to be safe. For general casts, use castTo.

Methods

getCurrentValue

valueGetCurrentValue

Arguments

:: (HasCallStack, MonadIO m, IsValue a)

=> a

obj: a GObject instance that implements AtkValueIface

-> m GValue

Deprecated: Since 2.12. Use valueGetValueAndTextinstead.

Gets the value of this object.

getIncrement

valueGetIncrement

Arguments

:: (HasCallStack, MonadIO m, IsValue a)

=> a

obj: a GObject instance that implements AtkValueIface

-> m Double

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

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.

Since: 2.12

getMaximumValue

valueGetMaximumValue

Arguments

:: (HasCallStack, MonadIO m, IsValue a)

=> a

obj: a GObject instance that implements AtkValueIface

-> m GValue

Deprecated: Since 2.12. Use valueGetRange instead.

Gets the maximum value of this object.

getMinimumIncrement

valueGetMinimumIncrement

Arguments

:: (HasCallStack, MonadIO m, IsValue a)

=> a

obj: a GObject instance that implements AtkValueIface

-> m GValue

Deprecated: Since 2.12. Use valueGetIncrement 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.

Since: 1.12

getMinimumValue

valueGetMinimumValue

Arguments

:: (HasCallStack, MonadIO m, IsValue a)

=> a

obj: a GObject instance that implements AtkValueIface

-> m GValue

Deprecated: Since 2.12. Use valueGetRange instead.

Gets the minimum value of this object.

getRange

valueGetRange

Arguments

:: (HasCallStack, MonadIO m, IsValue a)

=> a

obj: a GObject instance that implements AtkValueIface

-> m (Maybe Range)

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

Gets the range of this object.

Since: 2.12

getSubRanges

valueGetSubRanges

Arguments

:: (HasCallStack, MonadIO m, IsValue a)

=> a

obj: a GObject instance that implements AtkValueIface

-> m [Range]

Returns: an SList of Range which each of the subranges defined for this object. Free the returns list with g_slist_free().

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

Since: 2.12

getValueAndText

valueGetValueAndText

Arguments

:: (HasCallStack, MonadIO m, IsValue a)

=> a

obj: a GObject instance that implements AtkValueIface

-> m (Double, 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.

Since: 2.12

setCurrentValue

valueSetCurrentValue

Arguments

:: (HasCallStack, MonadIO m, IsValue a)

=> a

obj: a GObject instance that implements AtkValueIface

-> GValue

value: a Value which is the desired new accessible value.

-> m Bool

Returns: True if new value is successfully set, False otherwise.

Deprecated: Since 2.12. Use valueSetValue instead.

Sets the value of this object.

setValue

valueSetValue

Arguments

:: (HasCallStack, MonadIO m, IsValue a)

=> a

obj: a GObject instance that implements AtkValueIface

-> Double

newValue: a double which is the desired new accessible value.

-> m ()

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::value-changed signal emission.

Note for implementors: the deprecated valueSetCurrentValue 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.

Since: 2.12

Signals

valueChanged

type C_ValueValueChangedCallback = Ptr () -> CDouble -> CString -> Ptr () -> IO ()

Type for the callback on the (unwrapped) C side.

type ValueValueChangedCallback

Arguments

 = Double

value: the new value in a numerical form.

-> Text

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

-> IO ()

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".

Since: 2.12

afterValueValueChanged :: (IsValue a, MonadIO m) => a -> ValueValueChangedCallback -> m SignalHandlerId

Connect a signal handler for the “value-changed” signal, to be run after the default handler. When overloading is enabled, this is equivalent to

after value #valueChanged callback

genClosure_ValueValueChanged :: ValueValueChangedCallback -> IO Closure

Wrap the callback into a Closure.

mk_ValueValueChangedCallback :: C_ValueValueChangedCallback -> IO (FunPtr C_ValueValueChangedCallback)

Generate a function pointer callable from C code, from a C_ValueValueChangedCallback.

noValueValueChangedCallback :: Maybe ValueValueChangedCallback

A convenience synonym for Nothing :: Maybe ValueValueChangedCallback.

onValueValueChanged :: (IsValue a, MonadIO m) => a -> ValueValueChangedCallback -> m SignalHandlerId

Connect a signal handler for the “value-changed” signal, to be run before the default handler. When overloading is enabled, this is equivalent to

on value #valueChanged callback

wrap_ValueValueChangedCallback :: ValueValueChangedCallback -> C_ValueValueChangedCallback

Wrap a ValueValueChangedCallback into a C_ValueValueChangedCallback.