lv_observer.h

API reference for lv_observer.h

Summary

Functions

core/lv_observer.h:104function

lv_subject_set_external_data

Attaches external user data to an integer Subject with lifecycle management.

Associates arbitrary user-defined data with an LVGL observer and registers a destructor callback that will be automatically invoked when the observer is deleted. This enables:

Safe resource cleanup through the destructor mechanism
Contextual data storage for observer callbacks
Proper memory management for observer-related resources

void lv_subject_set_external_data(lv_subject_t *subject, void *data, void(*free_cb)(void *data))

Name	Type	Description
`subject`	`lv_subject_t *`	pointer to Subject
`data`	`void *`	User-defined data pointer to associate
`free_cb`	`void()(void data)`	Cleanup function called when: - Observer is explicitly deleted - Observed object is deleted - New data replaces current association NULL indicates no cleanup required

core/lv_observer.h:119function

lv_subject_set_int

Set value of an integer Subject and notify Observers.

void lv_subject_set_int(lv_subject_t *subject, int32_t value)

Name	Type	Description
`subject`	`lv_subject_t *`	pointer to Subject
`value`	`int32_t`	new value

core/lv_observer.h:141function

lv_subject_set_min_value_int

Set a minimum value for an integer subject

void lv_subject_set_min_value_int(lv_subject_t *subject, int32_t min_value)

Name	Type	Description
`subject`	`lv_subject_t *`	pointer to Subject
`min_value`	`int32_t`	the minimum value

core/lv_observer.h:148function

lv_subject_set_max_value_int

Set a maximum value for an integer subject

void lv_subject_set_max_value_int(lv_subject_t *subject, int32_t max_value)

Name	Type	Description
`subject`	`lv_subject_t *`	pointer to Subject
`max_value`	`int32_t`	the maximum value

core/lv_observer.h:164function

lv_subject_set_float

Set value of an float Subject and notify Observers.

void lv_subject_set_float(lv_subject_t *subject, float value)

Name	Type	Description
`subject`	`lv_subject_t *`	pointer to Subject
`value`	`float`	new value

core/lv_observer.h:185function

lv_subject_set_min_value_float

Set a minimum value for a float subject

void lv_subject_set_min_value_float(lv_subject_t *subject, float min_value)

Name	Type	Description
`subject`	`lv_subject_t *`	pointer to Subject
`min_value`	`float`	the minimum value

core/lv_observer.h:192function

lv_subject_set_max_value_float

Set a maximum value for a float subject

void lv_subject_set_max_value_float(lv_subject_t *subject, float max_value)

Name	Type	Description
`subject`	`lv_subject_t *`	pointer to Subject
`max_value`	`float`	the maximum value

core/lv_observer.h:249function

lv_subject_set_pointer

Set value of a pointer Subject and notify Observers (regardless of whether it changed).

void lv_subject_set_pointer(lv_subject_t *subject, void *ptr)

Name	Type	Description
`subject`	`lv_subject_t *`	pointer to Subject
`ptr`	`void *`	new value

core/lv_observer.h:277function

lv_subject_set_color

Set value of a color Subject and notify Observers if it changed.

void lv_subject_set_color(lv_subject_t *subject, lv_color_t color)

Name	Type	Description
`subject`	`lv_subject_t *`	pointer to Subject
`color`	`lv_color_t`	new value

core/lv_observer.h:419function

lv_obj_set_subject_increment_event_min_value

Set the minimum subject value to set by the event

void lv_obj_set_subject_increment_event_min_value(lv_obj_t *obj, lv_subject_increment_dsc_t *dsc, int32_t min_value)

Name	Type	Description
`obj`	`lv_obj_t *`	pointer to the Widget to which the event is attached
`dsc`	`lv_subject_increment_dsc_t *`	pointer to the descriptor returned by `lv_obj_add_subject_increment_event()`
`min_value`	`int32_t`	the minimum value to set

core/lv_observer.h:427function

lv_obj_set_subject_increment_event_max_value

Set the maximum subject value to set by the event

void lv_obj_set_subject_increment_event_max_value(lv_obj_t *obj, lv_subject_increment_dsc_t *dsc, int32_t max_value)

Name	Type	Description
`obj`	`lv_obj_t *`	pointer to the Widget to which the event is attached
`dsc`	`lv_subject_increment_dsc_t *`	pointer to the descriptor returned by `lv_obj_add_subject_increment_event()`
`max_value`	`int32_t`	the maximum value to set

core/lv_observer.h:436function

lv_obj_set_subject_increment_event_rollover

Set what to do when the min/max value is crossed.

void lv_obj_set_subject_increment_event_rollover(lv_obj_t *obj, lv_subject_increment_dsc_t *dsc, bool rollover)

Name	Type	Description
`obj`	`lv_obj_t *`	pointer to the Widget to which the event is attached
`dsc`	`lv_subject_increment_dsc_t *`	pointer to the descriptor returned by `lv_obj_add_subject_increment_event()`
`rollover`	`bool`	false: stop at the min/max value; true: jump to the other end

the subject also can have min/max values and always the smaller range will be considered

core/lv_observer.h:454function

lv_obj_add_subject_set_int_event

Set the value of an integer subject.

void lv_obj_add_subject_set_int_event(lv_obj_t *obj, lv_subject_t *subject, lv_event_code_t trigger, int32_t value)

Name	Type	Description
`obj`	`lv_obj_t *`	pointer to a widget
`subject`	`lv_subject_t *`	pointer to a subject to change
`trigger`	`lv_event_code_t`	the trigger on which the subject should be changed
`value`	`int32_t`	the value to set

core/lv_observer.h:465function

lv_obj_add_subject_set_float_event

Set the value of a float subject.

void lv_obj_add_subject_set_float_event(lv_obj_t *obj, lv_subject_t *subject, lv_event_code_t trigger, float value)

Name	Type	Description
`obj`	`lv_obj_t *`	pointer to a widget
`subject`	`lv_subject_t *`	pointer to a subject to change
`trigger`	`lv_event_code_t`	the trigger on which the subject should be changed
`value`	`float`	the value to set

core/lv_observer.h:475function

lv_obj_add_subject_set_string_event

Set the value of a string subject.

void lv_obj_add_subject_set_string_event(lv_obj_t *obj, lv_subject_t *subject, lv_event_code_t trigger, const char *value)

Name	Type	Description
`obj`	`lv_obj_t *`	pointer to a widget
`subject`	`lv_subject_t *`	pointer to a subject to change
`trigger`	`lv_event_code_t`	the trigger on which the subject should be changed
`value`	`const char *`	the value to set

Enums

core/lv_observer.h:33enum

lv_subject_type_t

Values for lv_subject_t's type field

Name	Value	Description
`LV_SUBJECT_TYPE_INVALID`	`0`	indicates Subject not initialized yet
`LV_SUBJECT_TYPE_NONE`	`1`	a null value like None or NILt
`LV_SUBJECT_TYPE_INT`	`2`	an int32_t
`LV_SUBJECT_TYPE_FLOAT`	`3`	a float, requires `LV_USE_FLOAT 1`
`LV_SUBJECT_TYPE_POINTER`	`4`	a void pointer
`LV_SUBJECT_TYPE_COLOR`	`5`	an `lv_color_t`
`LV_SUBJECT_TYPE_GROUP`	`6`	an array of Subjects
`LV_SUBJECT_TYPE_STRING`	`7`	a char pointer

Structs

struct

lv_subject_value_t

A common type to handle all the various observable types in the same way

Member	Type	Description
`num`	`int32_t`	Integer number (opacity, enums, booleans or "normal" numbers)
`pointer`	`const void *`	Constant pointer (string buffer, format string, font, cone text, etc.)
`color`	`lv_color_t`	Color
`float_v`	`float`	Floating point value

struct

_lv_subject_t

The Subject (an observable value)

Member	Type	Description
`ext_data`	`lv_ext_data_t`
`subs_ll`	`lv_ll_t`	Subscribers
`value`	`lv_subject_value_t`	Current value
`prev_value`	`lv_subject_value_t`	Previous value
`min_value`	`lv_subject_value_t`	Minimum value for min. int or float
`max_value`	`lv_subject_value_t`	Maximum value for max. int or float
`user_data`	`void *`	Additional parameter, can be used freely by user
`type`	`uint32_t`	One of the LV_SUBJECT_TYPE_... values
`size`	`uint32_t`	String buffer size or group length
`notify_restart_query`	`uint32_t`	If an Observer was deleted during notification, start notifying from the beginning.

Typedefs

core/lv_observer.h:80typedef

lv_observer_cb_t

typedef void(* lv_observer_cb_t) (lv_observer_t *observer, lv_subject_t *subject)

Callback called to notify Observer that Subject's value has changed

Used by 3 functions

lv_subject_add_observer — param observer_cb
lv_subject_add_observer_obj — param observer_cb
lv_subject_add_observer_with_target — param observer_cb

Dependencies

Indirect dependencies

lv_observer.h

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