I want to turn on/off dependency of two class properties based on the third property.

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lazymatlab 2023-2-12

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编辑： lazymatlab 2023-2-14

采纳的回答： chrisw23

在 MATLAB Online 中打开

I made a class "rect" for rectangle, with independent properties width, height and fix_aspect_ratio.

What I want to do is:

If fix_aspect_ratio is 0, width and height are independently modifiable.
If fix_aspect_ratio is 1, height/width should be maintained. When I change width, height should be modified to keep the ratio, and vise versa.

What I wrote:

classdef rect < handle
    properties
        width (1,1) double {mustBePositive} = 1
        height (1,1) double {mustBePositive} = 1
        fix_aspect_ratio (1,1) logical = 0
    end
    methods
        function obj = rect(width, height, fix_aspect_ratio)
            arguments
                width (1,1) double {mustBePositive} = 3
                height (1,1) double {mustBePositive} = 4
                fix_aspect_ratio (1,1) logical = 0
            end
            obj.width = width;
            obj.height = height;
            obj.fix_aspect_ratio = fix_aspect_ratio;
        end
        function set.width(obj, width)
            if obj.fix_aspect_ratio
                obj.height = obj.height * width/obj.width;
            end
            obj.width = width;
        end
        function set.height(obj, height)
            if obj.fix_aspect_ratio
                obj.width = obj.width * height/obj.height;
            end
            obj.height = height;
        end
    end
end

Problem:

When I try to change width, set.height is called, in which set.width is called, ... I get Maximum recursion error
When I try to change height, same thing.

Can I get any solution?

Thank you.

Kang.

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Answer 1

chrisw23 2023-2-13

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https://ww2.mathworks.cn/matlabcentral/answers/1911200-i-want-to-turn-on-off-dependency-of-two-class-properties-based-on-the-third-property#answer_1170110

Try to use Observed Properties

Save the listener handles as private properties and use the listeners 'Enabled' property to turn on/off the dependency as needed.

i.e.

obj.listenerObservedProp = addlistener(obj,'ObservedProp'...

obj.listenerObservedProp.Enabled = false

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lazymatlab 2023-2-13

编辑：lazymatlab 2023-2-13

在 MATLAB Online 中打开

Thank you @chrisw23.

I'm trying to apply setObsevable and listeners.

But I've encountered another problem.

classdef rect < handle
    properties (SetObservable)
        width
        height
    end
    properties
        fix_aspect_ratio (1,1) logical = 0
    end
    properties (Access = private)
        listener_width
        listener_height
    end
    methods
        function obj = rect(width, height, fix_aspect_ratio)
            arguments
                width (1,1) double {mustBePositive} = 3
                height (1,1) double {mustBePositive} = 4
                fix_aspect_ratio (1,1) logical = 0
            end
            obj.width = width;
            obj.height = height;
            obj.fix_aspect_ratio = fix_aspect_ratio;
            obj.listener_width = addlistener(obj, 'width', 'PreSet', @rect.propChange);
            obj.listener_height = addlistener(obj, 'height', 'PreSet', @rect.propChange);
        end
    end
    methods (Static)
        function propChange(metaProp, eventData)
            % How can I get the new value to set width or height?
        end
    end
end

In the propChange method, I need to know both the old and new value of width or height.

For example, if the original width was 3 and I want to change it to 6, height also has to be doubled.

But if I make the listener as Preset, the new value cannot be accessed because it is not passed yet,

while if I make the listener as Postset, the old value cannot be accessed because it is already discarded.

Can I pass the new value to listener callback?

Thank you.

chrisw23 2023-2-14

编辑：chrisw23 2023-2-14

why static ?

methods (private)

function propChange(obj,metaProp, eventData)

...

would give you access via obj and saving obj.lastPropVal should not be a problem using the prop set/get methods.

lazymatlab 2023-2-14

编辑：lazymatlab 2023-2-14

在 MATLAB Online 中打开

Thank you.

Solved by adding private properties for width and height.

Here is my new code:

classdef rect < handle
    properties (Dependent)
        width
        height
    end
    properties
        fix_aspect_ratio (1,1) logical = 0
    end
    properties (Access = private)
        p_width
        p_height
    end
    methods
        function obj = rect(width, height, fix_aspect_ratio)
            arguments
                width (1,1) double {mustBePositive} = 3
                height (1,1) double {mustBePositive} = 4
                fix_aspect_ratio (1,1) logical = 0
            end
            obj.p_width = width;
            obj.p_height = height;
            obj.fix_aspect_ratio = fix_aspect_ratio;
        end
        
        function width = get.width(obj)
            width = obj.p_width;
        end
        function height = get.height(obj)
            height = obj.p_height;
        end
        function set.width(obj, width)
            if obj.fix_aspect_ratio
                obj.p_height = obj.p_height * width/obj.p_width;
            end
            obj.p_width = width;
        end
        function set.height(obj, height)
            if obj.fix_aspect_ratio
                obj.p_width = obj.p_width * height/obj.p_height;
            end
            obj.p_height = height;
        end
    end
end

Your suggestion was helpful by the way.

Thank you.

Kang.

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I want to turn on/off dependency of two class properties based on the third property.

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I want to turn on/off dependency of two class properties based on the third property.

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