How can I access the properties of A class in B class without creating objects?

Question

fa wu 2023-8-30

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2014751-how-can-i-access-the-properties-of-a-class-in-b-class-without-creating-objects

评论： fa wu 2023-8-30

Here is the sample ， PropertyAccess allow ClassA get property ‘Prop1’，But you must creat a PropertyAccess object in Class A. This raises an issue as creating objects may consume a significant amount of memory (assuming PropertyAccess has a large number of properties, with one property being a 100000*100000 matrix). Therefore, is there a way to get the properties ‘Prop1’ of PropertyAccess in ClassA without creating objects

classdef PropertyAccess
    properties (GetAccess = {?ClassA, ?ClassB}, SetAccess = private)
        Prop1=5;
    end
    properties (Access = ?ClassC)
        Prop2=8;
    end
    methods (Static)
        function fun()
            X=PropertyAccess;
            disp(X.Prop1);
        end
    end
end

you must creat a PropertyAccess object in Class A.

classdef  ClassA < handle
    properties (SetObservable)  %或(SetObservable=true)
        x=1;
        y;
    end
    events
        kk
    end
    methods
        function obj=ClassA()
            obj.x=1;
            k=PropertyAccess(); %you must creat a PropertyAccess object in Class A.
            obj.y=k.Prop1;
        end
    end
end

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Answer 1

Steven Lord 2023-8-30

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Therefore, is there a way to get the properties ‘Prop1’ of PropertyAccess in ClassA without creating objects

If Prop1 were a Constant property of the PropertyAccess class, yes. You'd access that Constant property using the name of the class rather than an instance. But since in your example Prop1 is not Constant, you must have a specific instance of PropertyAccess whose Prop1 property you access.

It's like asking what's the Name property of the HumanBeing class. That question doesn't make sense unless you ask it on an instance of HumanBeing. The Name of the instance of HumanBeing representing me is "Steve".

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fa wu 2023-8-30

Thank you for your response; your analogy was very helpful for understanding, it's great!

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Answer 2

recent works 2023-8-30

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此回答的直接链接

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Yes, there is a way to get the properties of PropertyAccess in ClassA without creating objects. You can do this by using the matlab.mixin.SetGet class. The matlab.mixin.SetGet class provides a set of methods for getting and setting the properties of an object. To use the matlab.mixin.SetGet class, you need to make your class inherit from it.

Here is the modified code:

classdef PropertyAccess

properties (GetAccess = {?ClassA, ?ClassB}, SetAccess = private)

Prop1=5;

end

properties (Access = ?ClassC)

Prop2=8;

end

methods (Static)

function fun()

X=PropertyAccess;

disp(X.Prop1);

end

classdef ClassA < matlab.mixin.SetGet

properties (SetObservable) %或(SetObservable=true)

x=1;

y;

end

events

kk

end

methods

function obj=ClassA()

obj.x=1;

obj.y=PropertyAccess.Prop1; %No need to create PropertyAccess object

end

In this code, the class ClassA inherits from the matlab.mixin.SetGet class. This allows the class to access the properties of PropertyAccess without creating an object of PropertyAccess.

To get the property Prop1 of PropertyAccess, you can simply use the dot notation, as shown in the code.