## GAction GAction — An action interface |

## Synopsis

                        GAction;
    struct              GActionInterface;

    const gchar *       g_action_get_name                   (GAction *action);
    const GVariantType * g_action_get_parameter_type        (GAction *action);
    const GVariantType * g_action_get_state_type            (GAction *action);
    GVariant *          g_action_get_state_hint             (GAction *action);

    gboolean            g_action_get_enabled                (GAction *action);
    GVariant *          g_action_get_state                  (GAction *action);

    void                g_action_change_state               (GAction *action,
                                                             GVariant *value);
    void                g_action_activate                   (GAction *action,
                                                             GVariant *parameter);

## Object Hierarchy

      GInterface
       +----GAction

## Prerequisites

GAction requires GObject.

## Known Implementations

GAction is implemented by GSimpleAction.

## Properties

      "enabled"                  gboolean              : Read
      "name"                     gchar*                : Read
      "parameter-type"           GVariantType*         : Read
      "state"                    GVariant*             : Read
      "state-type"               GVariantType*         : Read

## Description

GAction represents a single named action.

The main interface to an action is that it can be activated with `g_action_activate()`. This results in the 'activate' signal being emitted. An activation has a GVariant parameter (which may be `NULL`). The correct type for the parameter is determined by a static parameter type (which is given at construction time).

An action may optionally have a state, in which case the state may be set with `g_action_change_state()`. This call takes a GVariant. The correct type for the state is determined by a static state type (which is given at construction time).

The state may have a hint associated with it, specifying its valid range.

GAction is merely the interface to the concept of an action, as described above. Various implementations of actions exist, including GSimpleAction and GtkAction.

In all cases, the implementing class is responsible for storing the name of the action, the parameter type, the enabled state, the optional state type and the state and emitting the appropriate signals when these change. The implementor responsible for filtering calls to `g_action_activate()` and `g_action_change_state()` for type safety and for the state being enabled.

Probably the only useful thing to do with a GAction is to put it inside of a GSimpleActionGroup.

## Details

### GAction

    typedef struct _GAction GAction;

### struct GActionInterface

    struct GActionInterface {
      GTypeInterface g_iface;

      /* virtual functions */
      const gchar *        (* get_name)             (GAction  *action);
      const GVariantType * (* get_parameter_type)   (GAction  *action);
      const GVariantType * (* get_state_type)       (GAction  *action);
      GVariant *           (* get_state_hint)       (GAction  *action);

      gboolean             (* get_enabled)          (GAction  *action);
      GVariant *           (* get_state)            (GAction  *action);

      void                 (* change_state)         (GAction  *action,
                                                     GVariant *value);
      void                 (* activate)             (GAction  *action,
                                                     GVariant *parameter);
    };

The virtual function table for GAction.

GTypeInterface `g_iface`; |
`get_name` () | the virtual function pointer for `g_action_get_name()`
`get_parameter_type` () | the virtual function pointer for `g_action_get_parameter_type()`
`get_state_type` () | the virtual function pointer for `g_action_get_state_type()`
`get_state_hint` () | the virtual function pointer for `g_action_get_state_hint()`
`get_enabled` () | the virtual function pointer for `g_action_get_enabled()`
`get_state` () | the virtual function pointer for `g_action_get_state()`
`change_state` () | the virtual function pointer for `g_action_change_state()`
`activate` () | the virtual function pointer for `g_action_activate()`. Note that GAction does not have an 'activate' signal but that implementations of it may have one.

Since 2.28

### g_action_get_name ()

    const gchar *       g_action_get_name                   (GAction *action);

Queries the name of `action`.

`action` : | a GAction
Returns : | the name of the action

Since 2.28

### g_action_get_parameter_type ()

    const GVariantType * g_action_get_parameter_type        (GAction *action);

Queries the type of the parameter that must be given when activating `action`.

When activating the action using `g_action_activate()`, the GVariant given to that function must be of the type returned by this function.

In the case that this function returns `NULL`, you must not give any GVariant, but `NULL` instead.

`action` : | a GAction
Returns : | the parameter type. [allow-none]

Since 2.28

### g_action_get_state_type ()

    const GVariantType * g_action_get_state_type            (GAction *action);

Queries the type of the state of `action`.

If the action is stateful (e.g. created with `g_simple_action_new_stateful()`) then this function returns the GVariantType of the state. This is the type of the initial value given as the state. All calls to `g_action_change_state()` must give a GVariant of this type and `g_action_get_state()` will return a GVariant of the same type.

If the action is not stateful (e.g. created with `g_simple_action_new()`) then this function will return `NULL`. In that case, `g_action_get_state()` will return `NULL` and you must not call `g_action_change_state()`.

`action` : | a GAction
Returns : | the state type, if the action is stateful. [allow-none]

Since 2.28

### g_action_get_state_hint ()

    GVariant *          g_action_get_state_hint             (GAction *action);

Requests a hint about the valid range of values for the state of `action`.

If `NULL` is returned it either means that the action is not stateful or that there is no hint about the valid range of values for the state of the action.

If a GVariant array is returned then each item in the array is a possible value for the state. If a GVariant pair (ie: two-tuple) is returned then the tuple specifies the inclusive lower and upper bound of valid values for the state.

In any case, the information is merely a hint. It may be possible to have a state value outside of the hinted range and setting a value within the range may fail.

The return value (if non-`NULL`) should be freed with `g_variant_unref()` when it is no longer required.

`action` : | a GAction
Returns : | the state range hint. [transfer full]

Since 2.28

### g_action_get_enabled ()

    gboolean            g_action_get_enabled                (GAction *action);

Checks if `action` is currently enabled.

An action must be enabled in order to be activated or in order to have its state changed from outside callers.

`action` : | a GAction
Returns : | whether the action is enabled

Since 2.28

### g_action_get_state ()

    GVariant *          g_action_get_state                  (GAction *action);

Queries the current state of `action`.

If the action is not stateful then `NULL` will be returned. If the action is stateful then the type of the return value is the type given by `g_action_get_state_type()`.

The return value (if non-`NULL`) should be freed with `g_variant_unref()` when it is no longer required.

`action` : | a GAction
Returns : | the current state of the action. [transfer full]

Since 2.28

### g_action_change_state ()

    void                g_action_change_state               (GAction *action,
                                                             GVariant *value);

Request for the state of `action` to be changed to `value`.

The action must be stateful and `value` must be of the correct type. See `g_action_get_state_type()`.

This call merely requests a change. The action may refuse to change its state or may change its state to something other than `value`. See `g_action_get_state_hint()`.

If the `value` GVariant is floating, it is consumed.

`action` : | a GAction
`value` : | the new state

Since 2.30

### g_action_activate ()

    void                g_action_activate                   (GAction *action,
                                                             GVariant *parameter);

Activates the action.

`parameter` must be the correct type of parameter for the action (ie: the parameter type given at construction time). If the parameter type was `NULL` then `parameter` must also be `NULL`.

`action` : | a GAction
`parameter` : | the parameter to the activation. [allow-none]

Since 2.28

## Property Details

### The `"enabled"` property

      "enabled"                  gboolean              : Read

If `action` is currently enabled.

If the action is disabled then calls to `g_action_activate()` and `g_action_change_state()` have no effect.

Default value: TRUE

Since 2.28

### The `"name"` property

      "name"                     gchar*                : Read

The name of the action. This is mostly meaningful for identifying the action once it has been added to a GActionGroup.

Default value: NULL

Since 2.28

### The `"parameter-type"` property

      "parameter-type"           GVariantType*         : Read

The type of the parameter that must be given when activating the action.

Since 2.28

### The `"state"` property

      "state"                    GVariant*             : Read

The state of the action, or `NULL` if the action is stateless.

Allowed values: GVariant<*>

Default value: NULL

Since 2.28

### The `"state-type"` property

      "state-type"               GVariantType*         : Read

The GVariantType of the state that the action has, or `NULL` if the action is stateless.

Since 2.28