Roller (lv_roller)

Overview

Roller allows you to simply select one option from a list by scrolling.

Parts and Styles

• LV_PART_MAIN The background of the roller uses all the typical background properties and text style properties. style_text_line_space adjusts the space between the options. When the Roller is scrolled and doesn't stop exactly on an option it will scroll to the nearest valid option automatically in anim_time milliseconds as specified in the style.

• LV_PART_SELECTED The selected option in the middle. Besides the typical background properties it uses the text style properties to change the appearance of the text in the selected area.

Usage

Set options

Options are passed to the Roller as a string with lv_roller_set_options(roller, options, LV_ROLLER_MODE_NORMAL). The options should be separated by \n. For example: "First\nSecond\nThird".

LV_ROLLER_MODE_INFINITE makes the roller circular.

You can select an option manually with lv_roller_set_selected(roller, id, LV_ANIM_ON), where id is the index of an option.

Get selected option

To get the index of the currently selected option use lv_roller_get_selected(roller).

lv_roller_get_selected_str(roller, buf, buf_size) will copy the name of the selected option to buf.

Visible rows

The number of visible rows can be adjusted with lv_roller_set_visible_row_count(roller, num).

This function calculates the height with the current style. If the font, line space, border width, etc. of the roller changes this function needs to be called again.

Events

• LV_EVENT_VALUE_CHANGED Sent when a new option is selected.

See the events of the Base object too.

Learn more about Events.

Keys

• LV_KEY_RIGHT/DOWN Select the next option

• LV_KEY_LEFT/UP Select the previous option

• LY_KEY_ENTER Apply the selected option (Send LV_EVENT_VALUE_CHANGED event)

Example

Simple Roller

C code  

 View on GitHub

#include "../../lv_examples.h"
#if LV_USE_ROLLER && 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) {
        char buf[32];
        lv_roller_get_selected_str(obj, buf, sizeof(buf));
        LV_LOG_USER("Selected month: %s\n", buf);
    }
}

/**
 * An infinite roller with the name of the months
 */
void lv_example_roller_1(void)
{
    lv_obj_t * roller1 = lv_roller_create(lv_screen_active());
    lv_roller_set_options(roller1,
                          "January\n"
                          "February\n"
                          "March\n"
                          "April\n"
                          "May\n"
                          "June\n"
                          "July\n"
                          "August\n"
                          "September\n"
                          "October\n"
                          "November\n"
                          "December",
                          LV_ROLLER_MODE_INFINITE);

    lv_roller_set_visible_row_count(roller1, 4);
    lv_obj_center(roller1);
    lv_obj_add_event(roller1, event_handler, LV_EVENT_ALL, NULL);
}

#endif

MicroPython code  

 View on GitHub MicroPython Simulator

def event_handler(e):
    code = e.get_code()
    obj = e.get_target_obj()
    if code == lv.EVENT.VALUE_CHANGED:
        option = " "*10
        obj.get_selected_str(option, len(option))
        print("Selected month: " + option.strip())

#
# An infinite roller with the name of the months
#

roller1 = lv.roller(lv.screen_active())
roller1.set_options("\n".join([
    "January",
    "February",
    "March",
    "April",
    "May",
    "June",
    "July",
    "August",
    "September",
    "October",
    "November",
    "December"]),lv.roller.MODE.INFINITE)

roller1.set_visible_row_count(4)
roller1.center()
roller1.add_event(event_handler, lv.EVENT.ALL, None)

---

Styling the roller

C code  

 View on GitHub

#include "../../lv_examples.h"
#if LV_USE_ROLLER && LV_FONT_MONTSERRAT_22 && 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) {
        char buf[32];
        lv_roller_get_selected_str(obj, buf, sizeof(buf));
        LV_LOG_USER("Selected value: %s", buf);
    }
}

/**
 * Roller with various alignments and larger text in the selected area
 */
void lv_example_roller_2(void)
{
    /*A style to make the selected option larger*/
    static lv_style_t style_sel;
    lv_style_init(&style_sel);
    lv_style_set_text_font(&style_sel, &lv_font_montserrat_22);
    lv_style_set_bg_color(&style_sel, lv_color_hex3(0xf88));
    lv_style_set_border_width(&style_sel, 2);
    lv_style_set_border_color(&style_sel, lv_color_hex3(0xf00));

    const char * opts = "1\n2\n3\n4\n5\n6\n7\n8\n9\n10";
    lv_obj_t * roller;

    /*A roller on the left with left aligned text, and custom width*/
    roller = lv_roller_create(lv_screen_active());
    lv_roller_set_options(roller, opts, LV_ROLLER_MODE_NORMAL);
    lv_roller_set_visible_row_count(roller, 2);
    lv_obj_set_width(roller, 100);
    lv_obj_add_style(roller, &style_sel, LV_PART_SELECTED);
    lv_obj_set_style_text_align(roller, LV_TEXT_ALIGN_LEFT, 0);
    lv_obj_set_style_bg_color(roller, lv_color_hex3(0x0f0), 0);
    lv_obj_set_style_bg_grad_color(roller, lv_color_hex3(0xafa), 0);
    lv_obj_set_style_bg_grad_dir(roller, LV_GRAD_DIR_VER, 0);
    lv_obj_align(roller, LV_ALIGN_LEFT_MID, 10, 0);
    lv_obj_add_event(roller, event_handler, LV_EVENT_ALL, NULL);
    lv_roller_set_selected(roller, 2, LV_ANIM_OFF);

    /*A roller on the middle with center aligned text, and auto (default) width*/
    roller = lv_roller_create(lv_screen_active());
    lv_roller_set_options(roller, opts, LV_ROLLER_MODE_NORMAL);
    lv_roller_set_visible_row_count(roller, 3);
    lv_obj_add_style(roller, &style_sel, LV_PART_SELECTED);
    lv_obj_align(roller, LV_ALIGN_CENTER, 0, 0);
    lv_obj_add_event(roller, event_handler, LV_EVENT_ALL, NULL);
    lv_roller_set_selected(roller, 5, LV_ANIM_OFF);

    /*A roller on the right with right aligned text, and custom width*/
    roller = lv_roller_create(lv_screen_active());
    lv_roller_set_options(roller, opts, LV_ROLLER_MODE_NORMAL);
    lv_roller_set_visible_row_count(roller, 4);
    lv_obj_set_width(roller, 80);
    lv_obj_add_style(roller, &style_sel, LV_PART_SELECTED);
    lv_obj_set_style_text_align(roller, LV_TEXT_ALIGN_RIGHT, 0);
    lv_obj_align(roller, LV_ALIGN_RIGHT_MID, -10, 0);
    lv_obj_add_event(roller, event_handler, LV_EVENT_ALL, NULL);
    lv_roller_set_selected(roller, 8, LV_ANIM_OFF);
}

#endif

MicroPython code  

 View on GitHub MicroPython Simulator

import fs_driver

def event_handler(e):
    code = e.get_code()
    obj = e.get_target_obj()
    if code == lv.EVENT.VALUE_CHANGED:
        option = " "*10
        obj.get_selected_str(option, len(option))
        print("Selected value: %s\n" + option.strip())

#
# Roller with various alignments and larger text in the selected area
#

# A style to make the selected option larger
style_sel = lv.style_t()
style_sel.init()

try:
    style_sel.set_text_font(lv.font_montserrat_22)
except:
    fs_drv = lv.fs_drv_t()
    fs_driver.fs_register(fs_drv, 'S')
    print("montserrat-22 not enabled in lv_conf.h, dynamically loading the font")

    # get the directory in which the script is running
    try:
        script_path = __file__[:__file__.rfind('/')] if __file__.find('/') >= 0 else '.'
    except NameError:
        print("Could not find script path")
        script_path = ''
    if script_path != '':
        try:
            font_montserrat_22 = lv.font_load("S:" + script_path + "/../../assets/font/montserrat-22.fnt")
            style_sel.set_text_font(font_montserrat_22)
        except:
            print("Cannot load font file montserrat-22.fnt")

style_sel.set_bg_color(lv.color_hex3(0xf88))
style_sel.set_border_width(2)
style_sel.set_border_color(lv.color_hex3(0xf00))

opts = "\n".join(["1","2","3","4","5","6","7","8","9","10"])

# A roller on the left with left aligned text, and custom width
roller = lv.roller(lv.screen_active())
roller.set_options(opts, lv.roller.MODE.NORMAL)
roller.set_visible_row_count(2)
roller.set_width(100)
roller.add_style(style_sel, lv.PART.SELECTED)
roller.set_style_text_align(lv.TEXT_ALIGN.LEFT, 0)
roller.set_style_bg_color(lv.color_hex3(0x0f0), 0)
roller.set_style_bg_grad_color(lv.color_hex3(0xafa), 0);
roller.align(lv.ALIGN.LEFT_MID, 10, 0)
roller.add_event(event_handler, lv.EVENT.ALL, None)
roller.set_selected(2, lv.ANIM.OFF)

# A roller in the middle with center aligned text, and auto (default) width
roller = lv.roller(lv.screen_active())
roller.set_options(opts, lv.roller.MODE.NORMAL)
roller.set_visible_row_count(3)
roller.add_style(style_sel, lv.PART.SELECTED)
roller.align(lv.ALIGN.CENTER, 0, 0)
roller.add_event(event_handler, lv.EVENT.ALL, None)
roller.set_selected(5, lv.ANIM.OFF)

# A roller on the right with right aligned text, and custom width
roller = lv.roller(lv.screen_active())
roller.set_options(opts, lv.roller.MODE.NORMAL)
roller.set_visible_row_count(4)
roller.set_width(80)
roller.add_style(style_sel, lv.PART.SELECTED)
roller.set_style_text_align(lv.TEXT_ALIGN.RIGHT, 0)
roller.align(lv.ALIGN.RIGHT_MID, -10, 0)
roller.add_event(event_handler, lv.EVENT.ALL, None)
roller.set_selected(8, lv.ANIM.OFF)

---

add fade mask to roller

C code  

 View on GitHub

#include "../../lv_examples.h"
//TODO
#if LV_USE_ROLLER && LV_DRAW_SW_COMPLEX && LV_BUILD_EXAMPLES && 0

static void mask_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);

    static int16_t mask_top_id = -1;
    static int16_t mask_bottom_id = -1;

    if(code == LV_EVENT_COVER_CHECK) {
        lv_event_set_cover_res(e, LV_COVER_RES_MASKED);

    }
    else if(code == LV_EVENT_DRAW_MAIN_BEGIN) {
        /* add mask */
        const lv_font_t * font = lv_obj_get_style_text_font(obj, LV_PART_MAIN);
        lv_coord_t line_space = lv_obj_get_style_text_line_space(obj, LV_PART_MAIN);
        lv_coord_t font_h = lv_font_get_line_height(font);

        lv_area_t roller_coords;
        lv_obj_get_coords(obj, &roller_coords);

        lv_area_t rect_area;
        rect_area.x1 = roller_coords.x1;
        rect_area.x2 = roller_coords.x2;
        rect_area.y1 = roller_coords.y1;
        rect_area.y2 = roller_coords.y1 + (lv_obj_get_height(obj) - font_h - line_space) / 2;

        lv_draw_mask_fade_param_t * fade_mask_top = lv_malloc(sizeof(lv_draw_mask_fade_param_t));
        lv_draw_mask_fade_init(fade_mask_top, &rect_area, LV_OPA_TRANSP, rect_area.y1, LV_OPA_COVER, rect_area.y2);
        mask_top_id = lv_draw_mask_add(fade_mask_top, NULL);

        rect_area.y1 = rect_area.y2 + font_h + line_space - 1;
        rect_area.y2 = roller_coords.y2;

        lv_draw_mask_fade_param_t * fade_mask_bottom = lv_malloc(sizeof(lv_draw_mask_fade_param_t));
        lv_draw_mask_fade_init(fade_mask_bottom, &rect_area, LV_OPA_COVER, rect_area.y1, LV_OPA_TRANSP, rect_area.y2);
        mask_bottom_id = lv_draw_mask_add(fade_mask_bottom, NULL);

    }
    else if(code == LV_EVENT_DRAW_POST_END) {
        lv_draw_mask_fade_param_t * fade_mask_top = lv_draw_mask_remove_id(mask_top_id);
        lv_draw_mask_fade_param_t * fade_mask_bottom = lv_draw_mask_remove_id(mask_bottom_id);
        lv_draw_mask_free_param(fade_mask_top);
        lv_draw_mask_free_param(fade_mask_bottom);
        lv_free(fade_mask_top);
        lv_free(fade_mask_bottom);
        mask_top_id = -1;
        mask_bottom_id = -1;
    }
}

/**
 * Add a fade mask to roller.
 */
void lv_example_roller_3(void)
{
    static lv_style_t style;
    lv_style_init(&style);
    lv_style_set_bg_color(&style, lv_color_black());
    lv_style_set_text_color(&style, lv_color_white());
    lv_style_set_border_width(&style, 0);
    lv_style_set_pad_all(&style, 0);
    lv_obj_add_style(lv_screen_active(), &style, 0);

    lv_obj_t * roller1 = lv_roller_create(lv_screen_active());
    lv_obj_add_style(roller1, &style, 0);
    lv_obj_set_style_bg_opa(roller1, LV_OPA_TRANSP, LV_PART_SELECTED);

#if LV_FONT_MONTSERRAT_22
    lv_obj_set_style_text_font(roller1, &lv_font_montserrat_22, LV_PART_SELECTED);
#endif

    lv_roller_set_options(roller1,
                          "January\n"
                          "February\n"
                          "March\n"
                          "April\n"
                          "May\n"
                          "June\n"
                          "July\n"
                          "August\n"
                          "September\n"
                          "October\n"
                          "November\n"
                          "December",
                          LV_ROLLER_MODE_NORMAL);

    lv_obj_center(roller1);
    lv_roller_set_visible_row_count(roller1, 3);
    lv_obj_add_event(roller1, mask_event_cb, LV_EVENT_ALL, NULL);
}
#endif

MicroPython code  

 View on GitHub MicroPython Simulator

pass

---

API

lv_roller.h