Checkbox (lv_checkbox)¶
Overview¶
The Checkbox object is created from a "tick box" and a label. When the Checkbox is clicked the tick box is toggled.
Parts and Styles¶
LV_PART_MAIN
The is the background of the Checkbox and it uses the text and all the typical background style properties.pad_column
adjusts the spacing between the tickbox and the labelLV_PART_INDICATOR
The "tick box" is a square that uses all the typical background style properties. By default, its size is equal to the height of the main part's font. Padding properties make the tick box larger in the respective directions.
The Checkbox is added to the default group (if it is set).
Usage¶
Text¶
The text can be modified with the lv_checkbox_set_text(cb, "New text")
function and will be dynamically allocated.
To set a static text,
use lv_checkbox_set_static_text(cb, txt)
. This way, only a pointer to txt
will be stored. The text then shouldn't be deallocated while the checkbox exists.
Check, uncheck, disable¶
You can manually check, un-check, and disable the Checkbox by using the common state add/clear function:
lv_obj_add_state(cb, LV_STATE_CHECKED); /*Make the chekbox checked*/
lv_obj_clear_state(cb, LV_STATE_CHECKED); /*MAke the checkbox unchecked*/
lv_obj_add_state(cb, LV_STATE_CHECKED | LV_STATE_DISABLED); /*Make the checkbox checked and disabled*/
Events¶
LV_EVENT_VALUE_CHANGED
Sent when the checkbox is toggled.LV_EVENT_DRAW_PART_BEGIN
andLV_EVENT_DRAW_PART_END
are sent for the following types:LV_CHECKBOX_DRAW_PART_BOX
The tickbox of the checkboxpart
:LV_PART_INDICATOR
draw_area
: the area of the tickboxrect_dsc
See the events of the Base object too.
Learn more about Events.
Keys¶
The following Keys are processed by the 'Buttons':
LV_KEY_RIGHT/UP
Go to toggled state if toggling is enabledLV_KEY_LEFT/DOWN
Go to non-toggled state if toggling is enabledLV_KEY_ENTER
Clicks the checkbox and toggles it
Note that, as usual, the state of LV_KEY_ENTER
is translated to LV_EVENT_PRESSED/PRESSING/RELEASED
etc.
Learn more about Keys.
Example¶
Simple Checkboxes¶
C code
GitHub#include "../../lv_examples.h"
#if LV_USE_CHECKBOX && LV_BUILD_EXAMPLES
static void event_handler(lv_event_t * e)
{
lv_event_code_t code = lv_event_get_code(e);
lv_obj_t * obj = lv_event_get_target(e);
if(code == LV_EVENT_VALUE_CHANGED) {
const char * txt = lv_checkbox_get_text(obj);
const char * state = lv_obj_get_state(obj) & LV_STATE_CHECKED ? "Checked" : "Unchecked";
LV_LOG_USER("%s: %s", txt, state);
}
}
void lv_example_checkbox_1(void)
{
lv_obj_set_flex_flow(lv_scr_act(), LV_FLEX_FLOW_COLUMN);
lv_obj_set_flex_align(lv_scr_act(), LV_FLEX_ALIGN_CENTER, LV_FLEX_ALIGN_START, LV_FLEX_ALIGN_CENTER);
lv_obj_t * cb;
cb = lv_checkbox_create(lv_scr_act());
lv_checkbox_set_text(cb, "Apple");
lv_obj_add_event_cb(cb, event_handler, LV_EVENT_ALL, NULL);
cb = lv_checkbox_create(lv_scr_act());
lv_checkbox_set_text(cb, "Banana");
lv_obj_add_state(cb, LV_STATE_CHECKED);
lv_obj_add_event_cb(cb, event_handler, LV_EVENT_ALL, NULL);
cb = lv_checkbox_create(lv_scr_act());
lv_checkbox_set_text(cb, "Lemon");
lv_obj_add_state(cb, LV_STATE_DISABLED);
lv_obj_add_event_cb(cb, event_handler, LV_EVENT_ALL, NULL);
cb = lv_checkbox_create(lv_scr_act());
lv_obj_add_state(cb, LV_STATE_CHECKED | LV_STATE_DISABLED);
lv_checkbox_set_text(cb, "Melon\nand a new line");
lv_obj_add_event_cb(cb, event_handler, LV_EVENT_ALL, NULL);
lv_obj_update_layout(cb);
}
#endif
def event_handler(e):
code = e.get_code()
obj = e.get_target()
if code == lv.EVENT.VALUE_CHANGED:
txt = obj.get_text()
if obj.get_state() & lv.STATE.CHECKED:
state = "Checked"
else:
state = "Unchecked"
print(txt + ":" + state)
lv.scr_act().set_flex_flow(lv.FLEX_FLOW.COLUMN)
lv.scr_act().set_flex_align(lv.FLEX_ALIGN.CENTER, lv.FLEX_ALIGN.START, lv.FLEX_ALIGN.CENTER)
cb = lv.checkbox(lv.scr_act())
cb.set_text("Apple")
cb.add_event_cb(event_handler, lv.EVENT.ALL, None)
cb = lv.checkbox(lv.scr_act())
cb.set_text("Banana")
cb.add_state(lv.STATE.CHECKED)
cb.add_event_cb(event_handler, lv.EVENT.ALL, None)
cb = lv.checkbox(lv.scr_act())
cb.set_text("Lemon")
cb.add_state(lv.STATE.DISABLED)
cb.add_event_cb(event_handler, lv.EVENT.ALL, None)
cb = lv.checkbox(lv.scr_act())
cb.add_state(lv.STATE.CHECKED | lv.STATE.DISABLED)
cb.set_text("Melon")
cb.add_event_cb(event_handler, lv.EVENT.ALL, None)
cb.update_layout()
Checkboxes as radio buttons¶
C code
GitHub#include "../../lv_examples.h"
#if LV_USE_CHECKBOX && LV_BUILD_EXAMPLES
static lv_style_t style_radio;
static lv_style_t style_radio_chk;
static uint32_t active_index_1 = 0;
static uint32_t active_index_2 = 0;
static void radio_event_handler(lv_event_t * e)
{
uint32_t * active_id = lv_event_get_user_data(e);
lv_obj_t * cont = lv_event_get_current_target(e);
lv_obj_t * act_cb = lv_event_get_target(e);
lv_obj_t * old_cb = lv_obj_get_child(cont, *active_id);
/*Do nothing if the container was clicked*/
if(act_cb == cont) return;
lv_obj_clear_state(old_cb, LV_STATE_CHECKED); /*Uncheck the previous radio button*/
lv_obj_add_state(act_cb, LV_STATE_CHECKED); /*Uncheck the current radio button*/
*active_id = lv_obj_get_index(act_cb);
LV_LOG_USER("Selected radio buttons: %d, %d", (int)active_index_1, (int)active_index_2);
}
static void radiobutton_create(lv_obj_t * parent, const char * txt)
{
lv_obj_t * obj = lv_checkbox_create(parent);
lv_checkbox_set_text(obj, txt);
lv_obj_add_flag(obj, LV_OBJ_FLAG_EVENT_BUBBLE);
lv_obj_add_style(obj, &style_radio, LV_PART_INDICATOR);
lv_obj_add_style(obj, &style_radio_chk, LV_PART_INDICATOR | LV_STATE_CHECKED);
}
/**
* Checkboxes as radio buttons
*/
void lv_example_checkbox_2(void)
{
/* The idea is to enable `LV_OBJ_FLAG_EVENT_BUBBLE` on checkboxes and process the
* `LV_EVENT_CLICKED` on the container.
* A variable is passed as event user data where the index of the active
* radiobutton is saved */
lv_style_init(&style_radio);
lv_style_set_radius(&style_radio, LV_RADIUS_CIRCLE);
lv_style_init(&style_radio_chk);
lv_style_set_bg_img_src(&style_radio_chk, NULL);
uint32_t i;
char buf[32];
lv_obj_t * cont1 = lv_obj_create(lv_scr_act());
lv_obj_set_flex_flow(cont1, LV_FLEX_FLOW_COLUMN);
lv_obj_set_size(cont1, lv_pct(40), lv_pct(80));
lv_obj_add_event_cb(cont1, radio_event_handler, LV_EVENT_CLICKED, &active_index_1);
for (i = 0;i < 5;i++) {
lv_snprintf(buf, sizeof(buf), "A %d", (int)i + 1);
radiobutton_create(cont1, buf);
}
/*Make the first checkbox checked*/
lv_obj_add_state(lv_obj_get_child(cont1, 0), LV_STATE_CHECKED);
lv_obj_t * cont2 = lv_obj_create(lv_scr_act());
lv_obj_set_flex_flow(cont2, LV_FLEX_FLOW_COLUMN);
lv_obj_set_size(cont2, lv_pct(40), lv_pct(80));
lv_obj_set_x(cont2, lv_pct(50));
lv_obj_add_event_cb(cont2, radio_event_handler, LV_EVENT_CLICKED, &active_index_2);
for (i = 0;i < 3;i++) {
lv_snprintf(buf, sizeof(buf), "B %d", (int)i + 1);
radiobutton_create(cont2, buf);
}
/*Make the first checkbox checked*/
lv_obj_add_state(lv_obj_get_child(cont2, 0), LV_STATE_CHECKED);
}
#endif
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API¶
Enums
Functions
-
lv_obj_t *lv_checkbox_create(lv_obj_t *parent)¶
Create a check box object
- Parameters
parent -- pointer to an object, it will be the parent of the new button
- Returns
pointer to the created check box
-
void lv_checkbox_set_text(lv_obj_t *obj, const char *txt)¶
Set the text of a check box.
txt
will be copied and may be deallocated after this function returns.- Parameters
cb -- pointer to a check box
txt -- the text of the check box. NULL to refresh with the current text.
Variables
-
const lv_obj_class_t lv_checkbox_class¶
-
struct lv_checkbox_t¶