Slider (lv_slider)
Overview
The Slider Widget looks like a Bar supplemented with a knob. The knob can be dragged to set a value. Just like Bar, Slider can be vertical or horizontal.
Parts and Styles
LV_PART_MAIN
The background of the slider. Uses all the typical background style properties.padding
makes the indicator smaller in the respective direction.LV_PART_INDICATOR
The indicator that shows the current state of the slider. Also uses all the typical background style properties.LV_PART_KNOB
A rectangle (or circle) drawn at the current value. Also uses all the typical background properties to describe the knob(s). By default, the knob is square (with an optional corner radius) with side length equal to the smaller side of the slider. The knob can be made larger with thepadding
values. Padding values can be asymmetric as well.
Usage
Value and range
To set an initial value use lv_slider_set_value(slider, new_value, LV_ANIM_ON / OFF). The
animation time is set by the styles' anim_time
property.
To specify the range (min, max values), lv_slider_set_range(slider, min, max) can be used. The default range is 0..100, and the default drawing direction is from left to right in horizontal mode and bottom to top in vertical mode. If the minimum value is greater than the maximum value, like 100..0, the drawing direction changes to the opposite direction.
Modes
The slider can be one of the following modes:
LV_SLIDER_MODE_NORMAL
A normal slider as described aboveLV_SLIDER_SYMMETRICAL
Draw the indicator form the zero value to current value. Requires negative minimum range and positive maximum range.LV_SLIDER_RANGE
Allows setting the start value as well by lv_bar_set_start_value(bar, new_value, LV_ANIM_ON / OFF). The start value has to be always smaller than the end value.
The mode can be changed with lv_slider_set_mode(slider, LV_SLIDER_MODE_...)
Knob-only mode
Normally, the slider can be adjusted either by dragging the knob, or by
clicking on the slider bar. In the latter case the knob moves to the
point clicked and slider value changes accordingly. In some cases it is
desirable to set the slider to react on dragging the knob only. This
feature is enabled by adding the LV_OBJ_FLAG_ADV_HITTEST
:
lv_obj_add_flag(slider, LV_OBJ_FLAG_ADV_HITTEST).
The extended click area (set by lv_obj_set_ext_click_area(slider, value)) increases to knob's click area.
Events
LV_EVENT_VALUE_CHANGED
Sent while the slider is being dragged or changed with keys. The event is sent continuously while the slider is being dragged.LV_EVENT_RELEASED
Sent when the slider has just been released.
Further Reading
Learn more about Base-Widget Events emitted by all Widgets.
Learn more about Events.
Keys
LV_KEY_UP/RIGHT
Increment the slider's value by 1LV_KEY_DOWN/LEFT
Decrement the slider's value by 1
Further Reading
Learn more about Keys.
Example
Simple Slider
C code
View on GitHub#include "../../lv_examples.h"
#if LV_USE_SLIDER && LV_BUILD_EXAMPLES
static void slider_event_cb(lv_event_t * e);
static lv_obj_t * slider_label;
/**
* A default slider with a label displaying the current value
*/
void lv_example_slider_1(void)
{
/*Create a slider in the center of the display*/
lv_obj_t * slider = lv_slider_create(lv_screen_active());
lv_obj_center(slider);
lv_obj_add_event_cb(slider, slider_event_cb, LV_EVENT_VALUE_CHANGED, NULL);
lv_obj_set_style_anim_duration(slider, 2000, 0);
/*Create a label below the slider*/
slider_label = lv_label_create(lv_screen_active());
lv_label_set_text(slider_label, "0%");
lv_obj_align_to(slider_label, slider, LV_ALIGN_OUT_BOTTOM_MID, 0, 10);
}
static void slider_event_cb(lv_event_t * e)
{
lv_obj_t * slider = lv_event_get_target(e);
char buf[8];
lv_snprintf(buf, sizeof(buf), "%d%%", (int)lv_slider_get_value(slider));
lv_label_set_text(slider_label, buf);
lv_obj_align_to(slider_label, slider, LV_ALIGN_OUT_BOTTOM_MID, 0, 10);
}
#endif
Slider with custom style
C code
View on GitHub#include "../../lv_examples.h"
#if LV_USE_SLIDER && LV_BUILD_EXAMPLES
/**
* Show how to style a slider.
*/
void lv_example_slider_2(void)
{
/*Create a transition*/
static const lv_style_prop_t props[] = {LV_STYLE_BG_COLOR, 0};
static lv_style_transition_dsc_t transition_dsc;
lv_style_transition_dsc_init(&transition_dsc, props, lv_anim_path_linear, 300, 0, NULL);
static lv_style_t style_main;
static lv_style_t style_indicator;
static lv_style_t style_knob;
static lv_style_t style_pressed_color;
lv_style_init(&style_main);
lv_style_set_bg_opa(&style_main, LV_OPA_COVER);
lv_style_set_bg_color(&style_main, lv_color_hex3(0xbbb));
lv_style_set_radius(&style_main, LV_RADIUS_CIRCLE);
lv_style_set_pad_ver(&style_main, -2); /*Makes the indicator larger*/
lv_style_init(&style_indicator);
lv_style_set_bg_opa(&style_indicator, LV_OPA_COVER);
lv_style_set_bg_color(&style_indicator, lv_palette_main(LV_PALETTE_CYAN));
lv_style_set_radius(&style_indicator, LV_RADIUS_CIRCLE);
lv_style_set_transition(&style_indicator, &transition_dsc);
lv_style_init(&style_knob);
lv_style_set_bg_opa(&style_knob, LV_OPA_COVER);
lv_style_set_bg_color(&style_knob, lv_palette_main(LV_PALETTE_CYAN));
lv_style_set_border_color(&style_knob, lv_palette_darken(LV_PALETTE_CYAN, 3));
lv_style_set_border_width(&style_knob, 2);
lv_style_set_radius(&style_knob, LV_RADIUS_CIRCLE);
lv_style_set_pad_all(&style_knob, 6); /*Makes the knob larger*/
lv_style_set_transition(&style_knob, &transition_dsc);
lv_style_init(&style_pressed_color);
lv_style_set_bg_color(&style_pressed_color, lv_palette_darken(LV_PALETTE_CYAN, 2));
/*Create a slider and add the style*/
lv_obj_t * slider = lv_slider_create(lv_screen_active());
lv_obj_remove_style_all(slider); /*Remove the styles coming from the theme*/
lv_obj_add_style(slider, &style_main, LV_PART_MAIN);
lv_obj_add_style(slider, &style_indicator, LV_PART_INDICATOR);
lv_obj_add_style(slider, &style_pressed_color, LV_PART_INDICATOR | LV_STATE_PRESSED);
lv_obj_add_style(slider, &style_knob, LV_PART_KNOB);
lv_obj_add_style(slider, &style_pressed_color, LV_PART_KNOB | LV_STATE_PRESSED);
lv_obj_center(slider);
}
#endif
Slider with extended drawer
C code
View on GitHub#include "../../lv_examples.h"
#if LV_USE_SLIDER && LV_BUILD_EXAMPLES
#define MAX_VALUE 100
#define MIN_VALUE 0
static void slider_event_cb(lv_event_t * e);
/**
* Show the current value when the slider is pressed by extending the drawer
*
*/
void lv_example_slider_3(void)
{
/*Create a slider in the center of the display*/
lv_obj_t * slider;
slider = lv_slider_create(lv_screen_active());
lv_obj_center(slider);
lv_slider_set_mode(slider, LV_SLIDER_MODE_RANGE);
lv_slider_set_range(slider, MIN_VALUE, MAX_VALUE);
lv_slider_set_value(slider, 70, LV_ANIM_OFF);
lv_slider_set_left_value(slider, 20, LV_ANIM_OFF);
lv_obj_add_event_cb(slider, slider_event_cb, LV_EVENT_ALL, NULL);
lv_obj_refresh_ext_draw_size(slider);
}
static void slider_event_cb(lv_event_t * e)
{
lv_event_code_t code = lv_event_get_code(e);
lv_obj_t * obj = lv_event_get_target(e);
/*Provide some extra space for the value*/
if(code == LV_EVENT_REFR_EXT_DRAW_SIZE) {
lv_event_set_ext_draw_size(e, 50);
}
else if(code == LV_EVENT_DRAW_MAIN_END) {
if(!lv_obj_has_state(obj, LV_STATE_PRESSED)) return;
lv_area_t slider_area;
lv_obj_get_coords(obj, &slider_area);
lv_area_t indic_area = slider_area;
lv_area_set_width(&indic_area, lv_area_get_width(&slider_area) * lv_slider_get_value(obj) / MAX_VALUE);
indic_area.x1 += lv_area_get_width(&slider_area) * lv_slider_get_left_value(obj) / MAX_VALUE;
char buf[16];
lv_snprintf(buf, sizeof(buf), "%d - %d", (int)lv_slider_get_left_value(obj), (int)lv_slider_get_value(obj));
lv_point_t label_size;
lv_text_get_size(&label_size, buf, LV_FONT_DEFAULT, 0, 0, LV_COORD_MAX, 0);
lv_area_t label_area;
label_area.x1 = 0;
label_area.x2 = label_size.x - 1;
label_area.y1 = 0;
label_area.y2 = label_size.y - 1;
lv_area_align(&indic_area, &label_area, LV_ALIGN_OUT_TOP_MID, 0, -10);
lv_draw_label_dsc_t label_draw_dsc;
lv_draw_label_dsc_init(&label_draw_dsc);
label_draw_dsc.color = lv_color_hex3(0x888);
label_draw_dsc.text = buf;
label_draw_dsc.text_local = true;
lv_layer_t * layer = lv_event_get_layer(e);
lv_draw_label(layer, &label_draw_dsc, &label_area);
}
}
#endif
Slider with opposite direction
C code
View on GitHub#include "../../lv_examples.h"
#if LV_USE_SLIDER && LV_BUILD_EXAMPLES
static void slider_event_cb(lv_event_t * e);
static lv_obj_t * slider_label;
/**
* Slider with opposite direction
*/
void lv_example_slider_4(void)
{
/*Create a slider in the center of the display*/
lv_obj_t * slider = lv_slider_create(lv_screen_active());
lv_obj_center(slider);
lv_obj_add_event_cb(slider, slider_event_cb, LV_EVENT_VALUE_CHANGED, NULL);
/*Reverse the direction of the slider*/
lv_slider_set_range(slider, 100, 0);
/*Create a label below the slider*/
slider_label = lv_label_create(lv_screen_active());
lv_label_set_text(slider_label, "0%");
lv_obj_align_to(slider_label, slider, LV_ALIGN_OUT_BOTTOM_MID, 0, 10);
}
static void slider_event_cb(lv_event_t * e)
{
lv_obj_t * slider = lv_event_get_target(e);
char buf[8];
lv_snprintf(buf, sizeof(buf), "%d%%", (int)lv_slider_get_value(slider));
lv_label_set_text(slider_label, buf);
lv_obj_align_to(slider_label, slider, LV_ALIGN_OUT_BOTTOM_MID, 0, 10);
}
#endif