[中文]

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

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

[中文]

Simple Roller

#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_cb(roller1, event_handler, LV_EVENT_ALL, NULL);
}

#endif

Styling the roller

#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_cb(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_cb(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_cb(roller, event_handler, LV_EVENT_ALL, NULL);
    lv_roller_set_selected(roller, 8, LV_ANIM_OFF);
}

#endif

add fade mask to roller

#include "../../lv_examples.h"

#if LV_USE_ROLLER && LV_DRAW_SW_COMPLEX && LV_BUILD_EXAMPLES && 1

static void generate_mask(lv_draw_buf_t * mask)
{
    /*Create a "8 bit alpha" canvas and clear it*/
    lv_obj_t * canvas = lv_canvas_create(lv_screen_active());
    lv_canvas_set_draw_buf(canvas, mask);
    lv_canvas_fill_bg(canvas, lv_color_white(), LV_OPA_TRANSP);

    lv_layer_t layer;
    lv_canvas_init_layer(canvas, &layer);

    /*Draw a label to the canvas. The result "image" will be used as mask*/
    lv_draw_rect_dsc_t rect_dsc;
    lv_draw_rect_dsc_init(&rect_dsc);
    rect_dsc.bg_grad.dir = LV_GRAD_DIR_VER;
    rect_dsc.bg_grad.stops[0].color = lv_color_black();
    rect_dsc.bg_grad.stops[1].color = lv_color_white();
    rect_dsc.bg_grad.stops[0].opa = LV_OPA_COVER;
    rect_dsc.bg_grad.stops[1].opa = LV_OPA_COVER;
    lv_area_t a = {0, 0, mask->header.w - 1, mask->header.h / 2 - 10};
    lv_draw_rect(&layer, &rect_dsc, &a);

    a.y1 = mask->header.h / 2 + 10;
    a.y2 = mask->header.h - 1;
    rect_dsc.bg_grad.stops[0].color = lv_color_white();
    rect_dsc.bg_grad.stops[1].color = lv_color_black();
    lv_draw_rect(&layer, &rect_dsc, &a);

    lv_canvas_finish_layer(canvas, &layer);

    /*Comment it to make the mask visible*/
    lv_obj_delete(canvas);
}

/**
 * Add a fade mask to roller.
 */
void lv_example_roller_3(void)
{
    lv_obj_set_style_bg_color(lv_screen_active(), lv_palette_main(LV_PALETTE_BLUE_GREY), 0);

    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_radius(&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_50, LV_PART_SELECTED);

    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, 4);

    /* Create the mask to make the top and bottom part of roller faded.
     * The width and height are empirical values for simplicity*/
    LV_DRAW_BUF_DEFINE_STATIC(mask, 130, 150, LV_COLOR_FORMAT_L8);
    LV_DRAW_BUF_INIT_STATIC(mask);

    generate_mask(&mask);
    lv_obj_set_style_bitmap_mask_src(roller1, &mask, 0);
}
#endif

API

lv_roller.h

lv_observer.h

lv_api_map_v8.h