[lvgl (4)] event and event bubble of the object

LVGL Official documents ：Welcome to the documentation of LVGL! — LVGL documentationhttps://docs.lvgl.io/master/index.html

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event (events)

Click on 、 rolling 、 Array changes 、 Repaint ……

Event type

• Enter the device event (Input device events)
• Graphic Events (Drawing events)
• Other events (Special events)
• Special events (Other events)
• Custom events (Custom events)

Look at the documents ~ Events — LVGL documentation

Add event

lv_obj_add_event_cb(obj, event_cb, event_code, user_data);

Parameters ： object , Handle (cb:callbackfunction, Callback function ), Event type , User data

Send events

lv_event_send(obj, event_cb, event_code, user_data);

Delete event

lv_obj_remove_event_cb(obj, event_cb);
lv_obj_remove_event_dsc(obj, event_dsc);    //event_dsc  yes  lv_obj_add_event_cb  Pointer returned 

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The simplest event ：

static void function()
{
    printf("test\n");
}

void mode(void)
{
    lv_obj_t * obj = lv_obj_create(lv_scr_act());
    
    lv_obj_add_event_cb(obj,function,LV_EVENT_CLICKED,NULL);    // Press the key to click , Call after release 
}

The called function can pass in parameters

function(lv_event_t * e)

typedef struct _lv_event_t {
    struct _lv_obj_t * target;    // Object that triggered the event 
    struct _lv_obj_t * current_target;    // The object whose parent triggers the event 
    lv_event_code_t code;    // Event code 
    void * user_data;    // User data 
    void * param;
    struct _lv_event_t * prev;
    uint8_t deleted : 1;
    uint8_t stop_processing : 1;
    uint8_t stop_bubbling : 1;
} lv_event_t;

as follows , Write a lighting interface

int count = 0;
static void function1(lv_event_t * e)
{


    lv_obj_t * obj = lv_event_get_target(e);        //  Get the part that triggers the event ( object )
    lv_event_code_t code = lv_event_get_code(e);    //  Get the current part ( object ) Triggered event code 
    lv_obj_t * label = lv_event_get_user_data(e);   //  Get the user data passed when adding events 


    if(count == 0 && code == LV_EVENT_PRESSED)
    {
        lv_label_set_text(label, "OPEN");
        lv_obj_set_style_bg_color(obj, lv_color_hex(0xc43e1c), 0);  //  Through local style ( Private style ) Set background color 
        printf("OPEN\n");
        count ++;
    }
    else if(count == 1 && code == LV_EVENT_PRESSED)
    {
        lv_label_set_text(label, "CLOSE");
        lv_obj_set_style_bg_color(obj, lv_color_hex(0xffffff), 0);  //  Through local style ( Private style ) Set background color 
        printf("CLOSE\n");
        count ++;
    }
    if(count==2)
        count = 0;

}


void lv_100ask_demo_course_2_2_6(void)
{

    /*  Create basic components ( object ) */
    lv_obj_t * obj = lv_obj_create(lv_scr_act());
    lv_obj_center(obj);    // Put it in the center 

    /*  establish label parts ( object ) */
    lv_obj_t * label = lv_label_create(lv_scr_act());
    lv_label_set_text(label, "CLOSE");   //  Set up label Displayed text 
    lv_obj_center(label);               //  Align the object with the center of its parent , The parent object here is the screen ：lv_scr_act()

    //  by obj1 Add event callback function , All event types can trigger the callback function 
    lv_obj_add_event_cb(obj, function1, LV_EVENT_ALL, label);// What's coming in is label, Can be set up label
}

The phenomenon ：

Click to turn on the light ：

• 

  Click to turn off the light ：

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Event Bubbling

If the object is enabled lv_obj_add_flag(obj, LV_OBJ_FLAG_EVENT_BUBBLE), All events of this object will be sent to the parent of this object . If The parent also enables LV_OBJ_FLAG_EVENT_BUBBLE, Then the event continues to be sent to his parent , And so on .

• lv_event_get_target(e); Get the current object that triggers the event . 
• lv_event_get_current_target(e); Get the parent object of the event bubble .

static void my_event_cb(lv_event_t * e)
{
    lv_obj_t * obj = lv_event_get_target(e);            //  Get the object that triggers the event 
    lv_obj_t * parent = lv_event_get_current_target(e); //  Get the parent object of the trigger event object ( Only when events bubble )
    lv_event_code_t code = lv_event_get_code(e);        //  Get the event code triggered by the current part 
    lv_obj_t * label = lv_event_get_user_data(e);       //  Get the user data passed when adding events 

    switch(code){
        case LV_EVENT_PRESSED:    // Keep pressing 
            lv_label_set_text(label, "LV_EVENT_PRESSED");
            /*  Parent  */
            lv_obj_set_style_bg_color(parent, lv_color_hex(0xc43e1c), 0);   //  Through local style ( Private style ) Set background color 
            /*  Trigger event itself object  */
            lv_obj_set_style_bg_color(obj, lv_color_hex(0xc43e1c), 0);      //  Through local style ( Private style ) Set background color 
            printf("LV_EVENT_PRESSED\n");
            break;
        case LV_EVENT_CLICKED:    // Click when releasing 
            lv_label_set_text(label, "LV_EVENT_CLICKED");
            lv_obj_remove_local_style_prop(parent, LV_STYLE_BG_COLOR, 0);   //  Delete through local style ( Private style ) Set the background color 
            lv_obj_remove_local_style_prop(obj, LV_STYLE_BG_COLOR, 0);      //  Delete through local style ( Private style ) Set the background color 
            printf("LV_EVENT_CLICKED\n");
            break;
        default:
            //printf("NONE\n");
            break;
    }
}

void lv_100ask_demo_course_2_2_6(void)
{
    /*  Create a base object  obj1 */
    lv_obj_t * obj1 = lv_obj_create(lv_scr_act());
    lv_obj_set_size(obj1, 450, 250);
    lv_obj_center(obj1);                                //  Align the object with the center of its parent , The parent object here is the screen ：lv_scr_act()

    /*  With  obj1  Create a base object  obj2 */
    lv_obj_t * obj2 = lv_obj_create(obj1);
    lv_obj_set_size(obj2, 400, 200);
    lv_obj_center(obj2);                                //  Align the object with the center of its parent , The parent object here is the screen ：obj1
    lv_obj_add_flag(obj2, LV_OBJ_FLAG_EVENT_BUBBLE);    //  Enable event bubbling , Propagate all received events to the parent 

    /*  With  obj2  Create a base object  obj3 */
    lv_obj_t * obj3 = lv_obj_create(obj2);
    lv_obj_set_size(obj3, 350, 150);
    lv_obj_center(obj3);                                //  Align the object with the center of its parent , The parent object here is the screen ：obj2
    lv_obj_add_flag(obj3, LV_OBJ_FLAG_EVENT_BUBBLE);    //  Enable event bubbling , Propagate all received events to the parent 

    /*  With  obj3  Create a base object  obj4 */
    lv_obj_t * obj4 = lv_obj_create(obj3);
    lv_obj_set_size(obj4, 300, 100);
    lv_obj_center(obj4);                                //  Align the object with the center of its parent , The parent object here is the screen ：obj3
    lv_obj_add_flag(obj4, LV_OBJ_FLAG_EVENT_BUBBLE);    //  Enable event bubbling , Propagate all received events to the parent 

    /*  Take screen as parent , Create a label parts ( object ) */
    lv_obj_t * label = lv_label_create(lv_scr_act());
    lv_label_set_text(label, "test");                               //  Set up label Displayed text 
    lv_obj_align_to(label, obj1, LV_ALIGN_OUT_TOP_MID, 0, 0);       //  take label be relative to obj1 alignment 

    //  Will give obj1 Add event callback function , All event types can trigger the callback function 
    lv_obj_add_event_cb(obj1, my_event_cb, LV_EVENT_ALL, label);
}

Ha ha ha ha ~ It's really interesting ~

The phenomenon ：

Click the middle object ：

Click on the third layer object ：

  Click on the second level object ：

  Outermost object ：

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Event description

An event callback function can be used for multiple objects

After we create an event handler function, it can be used by different objects .

An object can use multiple event callback functions

The object we create can be bound to multiple events , For example, an event deals with click type events , An event handles press type events, and so on .

other

If the incoming user data is different , An object can be bound to the same event callback function multiple times , Events will be called in the order they are added . for example ：

• lv_obj_add_event_cb(obj, my_clicked_event_cb, LV_EVENT_CLICKED, &num1);
• lv_obj_add_event_cb(obj, my_clicked_event_cb, LV_EVENT_CLICKED, &num2);

OK, In this way, we can realize the simple function call function , At least until now, it can be used as a light switch on the development board .