Custom keyboard

How-to
1

Description

Custom keyboard commands

What MCU/Processor/Board and compiler are you using?

Esp32

What do you want to achieve?

I have created a custom keyboard using a character map. I would like to implement a backspace and if possible an OK button which will send the text on the assigned text area to the machine.

What have you tried so far?

I have used the custom character but unlike the character keys it does nothing. Id like the backspace key to delete the character on its left in case i need to correct my input. Ive also used the custom ok key and it does nothing to. I had consulted the documentarions but didnt find any. I hope i am not missing something.

Code to reproduce

I’m on the ipad now. Ill edit the code later when im on the desktop.

The code block(s) should be formatted like:

/*You code here*/

Screenshot and/or video

2

You can use a custom callback for the keyboard and check what character was pressed.
This is a snippet that I am using:

// bind a callback to the keyboard
lv_obj_set_event_cb(kb, cb_pkeyboard);

// custom keyboard callback
static void cb_keyboard(lv_obj_t * obj, lv_event_t event){
    if(event == LV_EVENT_CLICKED){
        // get the character that was pressed
        const char * txt = lv_btnm_get_active_btn_text(obj);
        // compare with the backspace button text
        if(strcmp(txt, "<-")==0){
            // assuming you are storing entered text in the `input_buffer`
            if(strlen(input_buffer) > 0){
                input_buffer[strlen(input_buffer)-1] = 0;
            }
        // compare with your OK text
        }else if(strcmp(txt, "OK")==0){
            // proceed to some action
        }else{
            input_buffer[strlen(input_buffer)] = txt[0];
        }
        // get a textarea object binded to the keyboard
        lv_obj_t * ta = lv_kb_get_ta(obj);
        // update the text threre
        lv_ta_set_text(ta, input_buffer);
    }
}

There could be a more elegant way without input_buffer - using lv_ta_del_char(lv_obj_t *ta) (effectively backspace) and lv_ta_add_char(lv_obj_t *ta, uint32_t c), but I didn’t test it:

static void cb_keyboard(lv_obj_t * obj, lv_event_t event){
    if(event == LV_EVENT_CLICKED){
        // get a textarea object binded to the keyboard
        lv_obj_t * ta = lv_kb_get_ta(obj);
        // get the character that was pressed
        const char * txt = lv_btnm_get_active_btn_text(obj);
        // compare with the backspace button text
        if(strcmp(txt, "<-")==0){
            lv_ta_del_char(ta);
        // compare with your OK text
        }else if(strcmp(txt, "OK")==0){
            // proceed to some action
        }else{
            lv_ta_add_text(ta, txt);
        }
    }
}
3 Likes
3

I strongly suggest using the more elegant of the two approaches that @Stepan_Snigirev suggested. There is no need to have a separate buffer in addition to the text area.

4

I’m amazed. Big thanks @Stepan_Snigirev and @embeddedt.