Why does the callback function create an 'meta.property 'object

When you wanna instantiate an object. First you need creat a class or you already have a class. Then you use a class to instantiate an object.

Or you already object, then you copy a object .

But look this code. I make a breakingpoint in 15th line of ClassB 'switch src.Name',then excute:

＞＞ obj_a=ClassA;

＞＞ obj_b=ClassB(obj_a);

＞＞ obj_a.x=3;

When the program runs to 15th line of ClassB.m . I found 'src' is a 'meta.property 'object! Why does the callback function create an 'meta.property 'object? How does the callback function create an 'meta.property 'object?

I check the addlistener ,this function allow to input 'meta.property 'object for 'PropertyName' ,but it dose not creat a 'meta.property 'object.

Obviously 'x' as the input arguments of the addlistener function(7th line of ClassB.m) is the character, not the 'meta.property' object.

ClassA.m

classdef  ClassA < handle
    properties (SetObservable)  %或(SetObservable=true)
        x=1;
        y=2;
    end
end

ClassB.m

classdef  ClassB < handle
    methods
        %构造函数，输入参数event_obj是产生事件的对象
        function obj = ClassB(event_obj)
            %为x的PreSet、为y的PostSet分别添加两个听众
            if nargin > 0
                addlistener(event_obj,'x','PreSet',@ClassB.eventsCBFunc);
                addlistener(event_obj,'y','PostSet',@ClassB.eventsCBFunc);
            end
        end
    end
    methods (Static)
        %两个听众的回调函数
        function eventsCBFunc(src,evnt)
            switch src.Name
                case 'x'
                    fprintf(['Current event:' evnt.EventName]);
                    fprintf(1,' \n x is %s\n',num2str(evnt.AffectedObject.x))
                case 'y'
                    fprintf(['Current event:' evnt.EventName]);
                    fprintf(1,' \n y is %s\n',num2str(evnt.AffectedObject.y))
            end
        end
    end
end

Answer 1

[fa wu]

I got the answer

the documents Listen for Changes to Property Values：Define Callback Function for Property Event

The listener executes the callback function when MATLAB® triggers the property event. Define the callback function to have two specific arguments, which are passed to the function automatically when called by the listener:

• Event source — a meta.property object describing the object that is the source of the property event
• Event data — a event.PropertyEvent object containing information about the event