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

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fa wu
fa wu 2023-8-14
回答： fa wu 2023-8-14
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

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采纳的回答

fa wu
fa wu 2023-8-14
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

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