Slider (lv_slider)

The Slider Widget looks like a Bar (lv_bar) supplemented with a knob. The knob can be dragged to set the Slider's value.

Overview

The Slider Widget looks like a Bar (lv_bar) supplemented with a knob. The knob can be dragged to set the Slider's value. Like Bar, a Slider can be vertical or horizontal.

Parts and Styles

• LV_PART_MAIN The background of the Slider. Uses 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 the typical background style properties.
• LV_PART_KNOB A rectangle (or circle) drawn at the current value; also uses the typical background style properties to describe the knob(s). By default, the knob is round (radius-style can modify this) with side length equal to the smaller dimension of the Slider. The knob can be made larger with the padding values. Padding values can be asymmetric as well.

Usage

Value, range and orientation

Once a Slider is created, it has:

• value == 0
• default range of [0..100],
• horizontal orientation, with
• default width of approximately 2 inches (according to configured value of LV_DPI_DEF),
• default height of approximately 1/10 inch (according to configured value of LV_DPI_DEF).

To set different values use:

• lv_slider_set_value(slider, new_value, LV_ANIM_ON/OFF) (animation time is set by the styles' anim_time property);

• lv_slider_set_range(slider, min , max); and

• for orientation, width and height, simply set width and height properties;

• lv_slider_set_orientation(slider, orientation) to override orientation caused by width and height. Valid values for orientation are:

  • LV_SLIDER_ORIENTATION_AUTO
  • LV_SLIDER_ORIENTATION_HORIZONTAL
  • LV_SLIDER_ORIENTATION_VERTICAL

The default drawing direction is from left to right in horizontal orientation and bottom to top in vertical orientation. If the minimum value is set to be greater than the maximum value (e.g. [100..0]), the drawing direction is reversed.

Modes

The Slider can be in one of the following modes:

• LV_SLIDER_MODE_NORMAL A normal Slider as described above (default)
• LV_SLIDER_SYMMETRICAL Draw the indicator from 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(slider, new_value, LV_ANIM_ON/OFF). The start value must always be 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 the 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 flag: lv_obj_add_flag(slider, LV_OBJ_FLAG_ADV_HITTEST).

Any extended click area (set by lv_obj_set_ext_click_area(slider, value)) increases the knob's click area.

Data binding

To get familiar with observers, subjects, and data bindings in general, visit the Observer page.

This method of subscribing to an integer Subject affects a Slider Widget's integer value directly. Note that this is a two-way binding (Subject <===> Widget), so an end user's direct interaction with the Slider Widget updates the Subject's value and vice versa.

It supports integer and float subjects.

• lv_slider_bind_value(slider, &subject)

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 once when Slider is released.

Keys

• LV_KEY_UP/RIGHT Increment Slider's value by 1.
• LV_KEY_DOWN/LEFT Decrement Slider's value by 1.

Examples

Simple Slider

Slider with custom style

Slider with extended drawer

Slider with opposite direction

API