Input devices

An input device usually means:

Pointer-like input device like touchpad or mouse
Keypads like a normal keyboard or simple numeric keypad
Encoders with left/right turn and push options
External hardware buttons which are assigned to specific points on the screen

important:: Before reading further, please read the Porting section of Input devices

Pointers

Cursor

Pointer input devices (like a mouse) can have a cursor.

...
lv_indev_t * mouse_indev = lv_indev_create();
...
LV_IMG_DECLARE(mouse_cursor_icon);                          /*Declare the image source.*/
lv_obj_t * cursor_obj = lv_image_create(lv_screen_active());      /*Create an image object for the cursor */
lv_image_set_src(cursor_obj, &mouse_cursor_icon);           /*Set the image source*/
lv_indev_set_cursor(mouse_indev, cursor_obj);               /*Connect the image  object to the driver*/

Note that the cursor object should have lv_obj_remove_flag(cursor_obj, LV_OBJ_FLAG_CLICKABLE). For images, clicking is disabled by default.

Gestures

Pointer input devices can detect basic gestures. By default, most of the widgets send the gestures to its parent, so finally the gestures can be detected on the screen object in a form of an LV_EVENT_GESTURE event. For example:

void my_event(lv_event_t * e)
{
  lv_obj_t * screen = lv_event_get_current_target(e);
  lv_dir_t dir = lv_indev_get_gesture_dir(lv_indev_active());
  switch(dir) {
    case LV_DIR_LEFT:
      ...
      break;
    case LV_DIR_RIGHT:
      ...
      break;
    case LV_DIR_TOP:
      ...
      break;
    case LV_DIR_BOTTOM:
      ...
      break;
  }
}

...

lv_obj_add_event_cb(screen1, my_event, LV_EVENT_GESTURE, NULL);

To prevent passing the gesture event to the parent from an object use lv_obj_remove_flag(obj, LV_OBJ_FLAG_GESTURE_BUBBLE).

Note that, gestures are not triggered if an object is being scrolled.

If you did some action on a gesture you can call lv_indev_wait_release(lv_indev_active()) in the event handler to prevent LVGL sending further input device related events.

Keypad and encoder

You can fully control the user interface without a touchpad or mouse by using a keypad or encoder(s). It works similar to the TAB key on the PC to select an element in an application or a web page.

Groups

Objects you want to control with a keypad or encoder need to be added to a Group. In every group there is exactly one focused object which receives the pressed keys or the encoder actions. For example, if a Text area is focused and you press some letter on a keyboard, the keys will be sent and inserted into the text area. Similarly, if a Slider is focused and you press the left or right arrows, the slider's value will be changed.

You need to associate an input device with a group. An input device can send key events to only one group but a group can receive data from more than one input device.

To create a group use lv_group_t * g = lv_group_create() and to add an object to the group use lv_group_add_obj(g, obj).

To associate a group with an input device use lv_indev_set_group(indev, g).

Keys

There are some predefined keys which have special meaning:

LV_KEY_NEXT: Focus on the next object
LV_KEY_PREV: Focus on the previous object
LV_KEY_ENTER: Triggers LV_EVENT_PRESSED, LV_EVENT_CLICKED, or LV_EVENT_LONG_PRESSED etc. events
LV_KEY_UP: Increase value or move upwards
LV_KEY_DOWN: Decrease value or move downwards
LV_KEY_RIGHT: Increase value or move to the right
LV_KEY_LEFT: Decrease value or move to the left
LV_KEY_ESC: Close or exit (E.g. close a Drop down list)
LV_KEY_DEL: Delete (E.g. a character on the right in a Text area)
LV_KEY_BACKSPACE: Delete a character on the left (E.g. in a Text area)
LV_KEY_HOME: Go to the beginning/top (E.g. in a Text area)
LV_KEY_END: Go to the end (E.g. in a Text area)

The most important special keys in your read_cb() function are:

You should translate some of your keys to these special keys to support navigation in a group and interact with selected objects.

Usually, it's enough to use only LV_KEY_LEFT and LV_KEY_RIGHT because most objects can be fully controlled with them.

With an encoder you should use only LV_KEY_LEFT, LV_KEY_RIGHT, and LV_KEY_ENTER.

Edit and navigate mode

Since a keypad has plenty of keys, it's easy to navigate between objects and edit them using the keypad. But encoders have a limited number of "keys" and hence it is difficult to navigate using the default options. Navigate and Edit modes are used to avoid this problem with encoders.

In Navigate mode, an encoder's LV_KEY_LEFT or LV_KEY_RIGHT is translated to LV_KEY_NEXT or LV_KEY_PREV. Therefore, the next or previous object will be selected by turning the encoder. Pressing LV_KEY_ENTER will change to Edit mode.

In Edit mode, LV_KEY_NEXT and LV_KEY_PREV is usually used to modify an object. Depending on the object's type, a short or long press of LV_KEY_ENTER changes back to Navigate mode. Usually, an object which cannot be pressed (like a Slider) leaves Edit mode upon a short click. But with objects where a short click has meaning (e.g. Button), a long press is required.

Default group

Interactive widgets - such as buttons, checkboxes, sliders, etc. - can be automatically added to a default group. Just create a group with lv_group_t * g = lv_group_create() and set the default group with lv_group_set_default(g)

Don't forget to assign one or more input devices to the default group with lv_indev_set_group(my_indev, g).

Styling

If an object is focused either by clicking it via touchpad or focused via an encoder or keypad it goes to the LV_STATE_FOCUSED state. Hence, focused styles will be applied to it.

If an object switches to edit mode it enters the LV_STATE_FOCUSED | LV_STATE_EDITED states so these style properties will be shown.

For a more detailed description read the Style section.

API