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docs(observer): add more information about subject groups

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Gabor Kiss-Vamosi
2023-11-27 16:35:31 +01:00
committed by GitHub
parent 2b0587197c
commit 81d8a110b1
1 changed files with 28 additions and 16 deletions
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docs/others/observer.rst
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@@ -122,7 +122,9 @@ Observer
********
Subscribe to a subject
----------------------
----------------------ubject groups can be created. For the above example it looks like this:
to subscribe to a subject the following function can be used:
@@ -176,50 +178,60 @@ To unsubscribe from a subject with all widgets you can use:
Subject groups
**************
There are cases when a subject changes, the value of some other subjects are also required.
As practical example imagine an instrument which measures either voltage or current.
There are cases when a subject changes and the value of some other subjects are also required by the observer.
As a practical example imagine an instrument which measures either voltage or current.
To display the measured value on a label 3 things are required:
1. What we measure (current or voltage)?
1. What do we measure (current or voltage)?
2. What is the measured value?
3. What is the unit (mV, V, mA, A)?
3. What is the range or unit (mV, V, mA, A)?
What any of these 3 parameters changes the label needs to be updated,
When any of these 3 parameters changes the label needs to be updated,
and it needs to know all 3 parameters to compose its text.
For these kind of scenarios subject groups can be created.
For the above example it looks like this:
To handle this you can create an array from some existing subjects and pass
this array as a parameter when you initialize a subject with group type.
.. code:: c
static lv_subject_t * subject_list[3] = {&subject_1, &subject_2, &subject_3};
lv_subject_init_group(&subject_all, subject_list, 3); /*The last parameter is the number of elements*/
You can add observers to subject groups in the regular way.
The trick is that when any element of the group is notified the subject group will be notified too.
The above Voltage/Current measurement example looks like this in the practice:
.. code:: c
lv_obj_t * label = lv_label_create(lv_screen_active());
lv_subject_t subject_mode; //Voltage or Current
lv_subject_t subject_value; //Measured value
lv_subject_t subject_unit; //The unit
lv_subject_t subject_all; //It will be the subject group
lv_subject_t subject_list[3] = {&subject_mode, &subject_value, &subject_unit}; //The elements of the group
lv_subject_t * subject_list[3] = {&subject_mode, &subject_value, &subject_unit}; //The elements of the group
lv_subject_init_int(&subject_mode, 0); //Let's say 0 is Voltage, 1 is Current
lv_subject_init_int(&subject_value, 0);
lv_subject_init_pointer(&subject_unit, "V");
lv_subject_init_group(&subject_all, subject_list, 3);
lv_subject_add_observer(&subject_all, all_observer_cb, some_label, NULL);
lv_subject_add_observer_obj(&subject_all, all_observer_cb, label, NULL);
...
static void some_observer_cb(lv_subject_t * subject, lv_observer_t * observer)
static void all_observer_cb(lv_subject_t * subject, lv_observer_t * observer)
{
lv_obj_t * label = lv_observer_get_target(observer);
lv_subject_t * subject_mode = lv_subject_get_group_element(subject, 0)
lv_subject_t * subject_value = lv_subject_get_group_element(subject, 1)
lv_subject_t * subject_unit = lv_subject_get_group_element(subject, 2)
lv_subject_t * subject_mode = lv_subject_get_group_element(subject, 0);
lv_subject_t * subject_value = lv_subject_get_group_element(subject, 1);
lv_subject_t * subject_unit = lv_subject_get_group_element(subject, 2);
int32_t mode = lv_subject_get_int(subject_mode);
int32_t value = lv_subject_get_int(subject_value);
const char * unit = lv_subject_get_pointer(subject_unit);
lv_label_set_text_fmt(label, "%s: %d %s, mode ? "Current" : "Voltage", value, unit);
lv_label_set_text_fmt(label, "%s: %d %s", mode ? "Current" : "Voltage", value, unit);
}