How to execute a function after the value of a property changed? Problems with callback function

Question

Sven 2013-12-4

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/108582-how-to-execute-a-function-after-the-value-of-a-property-changed-problems-with-callback-function

编辑： per isakson 2013-12-7

Hi, I would like to execute a function every time a particular property of an object has changed. More specifically, I have two properties in my class (PW - not observable, PMV Observable). I would like PMV to change every time PW changes. Below is how far I have gotten in order to achieve this:

*START CODE*

classdef RB < handle
       properties
            PW  = [];
       end
       properties(SetObservable)
            PMV  = [];
       end
       methods
            function this = RB()
                addlistener(this,'PMV','PostSet',@RB.ChgPMV);
            end
            function ChgPMV(this)
                 disp('got here');
                 this.PW = this.PMV ./ sum(this.PMV);
            end
       end
end

*END CODE*

Unfortunately it doesnt work... This is what I get:

>> a=RB() a = RB with properties:

     PW: []
    PMV: []
>> a.PMV=[10,20]
Warning: Error occurred while executing callback:
Undefined function 'RB.ChgPMV' for input arguments of type 'meta.property'. 
a = 
  RB with properties:
     PW: []
    PMV: [10 20]
>>

My question now is: How do I need to change the code such that the ChgPMV function executes? Thank you for any hint Sven

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Answer 1

per isakson 2013-12-7

1
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https://ww2.mathworks.cn/matlabcentral/answers/108582-how-to-execute-a-function-after-the-value-of-a-property-changed-problems-with-callback-function#answer_117610

编辑：per isakson 2013-12-7

在 MATLAB Online 中打开

There are two problems

@RB.ChgPMV (this call would work with static methods) [see the answer of Sven]
function ChgPMV( this ) Matlab adds a couple of arguments, which need to be matched by input arguments

Now

    >> a=RB();
    >> a.PMV = 1;
    got here

where

    classdef RB < handle
        properties
            PW  = [];
        end
        properties( SetObservable )
            PMV  = [];
        end
        methods
            function this = RB()
                addlistener( this,'PMV','PostSet',@this.ChgPMV);
            end
            function ChgPMV( this, varargin )
                disp('got here');
                this.PW = this.PMV ./ sum(this.PMV);
            end
        end
    end

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Answer 2

Sven 2013-12-6

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https://ww2.mathworks.cn/matlabcentral/answers/108582-how-to-execute-a-function-after-the-value-of-a-property-changed-problems-with-callback-function#answer_117497

编辑：Sven 2013-12-6

在 MATLAB Online 中打开

If all of the observation of PMV is done by the RB class itself, so there's actually a better/cleaner way to do what you're trying to do. Here I just make PMV a simple property and PW a dependent property. Then I use the .set() method of PMV to perform the update of PW.

Does this do what you expected?

classdef RB < handle
       properties
            PMV  = [];
       end
       properties (Dependent)
            PW
       end
       methods
            function set.PMV(this, newVal)
                this.PMV = newVal;
                this.ChgPMV()
            end
            function ChgPMV(this)
                 disp('got here');
                 this.PW = this.PMV ./ sum(this.PMV);
            end
       end
end

There's nothing stopping you from making PMV SetObservable for other purposes, but it's not necessary to achieve what you described.

Oh, and if you really wanted to make your original example work, just use this line in your constructor:

addlistener(this,'PMV','PostSet',@(src,eventData)this.ChgPMV);

You'll notice that I changed RB (class name) to this (the object in scope that you want to listen to), and declared the two default input arguments to the listener which you don't really use but would be added automatically if you didn't declare them)

I hope that answered your question. If so, remember to hit "accept".

Thanks, Sven.