MATLAB: How to add Dynamic Properties to the value class in MATLAB 8.0 (R2012b)

addpropdynamicpropshandleMATLABstructuresvalue

I have a Value Class 'myClass' and I would like to add properties to an instance of this class, the names of which are available only at the run time. Hence I would like to add these properties Dynamically to an instance of the class myClass.

I am not able to Sub-Class from DYNAMICPROPS because that would make my class a handle class.

Best Answer

In order to have dynamically added properties for the instances of your value class, we would recommend that you have a structure (a variable of type Struct) as one of the properties of your class and then add fields to this structure dynamically (either during the construction of the objects or there after). You can add fields to the structure dynamically using a feature in the MATLAB Language called 'Dynamic Field access' for structures.

Please refer to the documentation page here:

http://www.mathworks.com/help/releases/R2012b/matlab/ref/specialcharacters.html

A quick example is provided in this solution, myClass.m, (See attached) that implements a constructor that takes two property name and value pairs that are added to the object during its construction. myClass also has a function called addprops that adds more fields to this structure. Here is how the output looks like at the MATLAB Command Prompt.

>> myDynamicProp1 = 'prop1';
>> myDynamicProp2 = 'prop2';
>> obj = myClass(myDynamicProp1, 5, myDynamicProp2, 7.8)
obj = 
   myClass
   Properties:
     myStruct: [1x1 struct]
   Methods
>> newObj = obj.addprop('prop3', 'Hello')
newObj = 
   myClass
   Properties:
     myStruct: [1x1 struct]
   Methods
>> newObj.myStruct
ans = 
     prop1: 5
     prop2: 7.8000
     prop3: 'Hello'
>>

The MATLAB script file tsTest.m (see attached) has the same commands as shown above.

Related Solutions

MATLAB: How to set object property to Abstract class

To specify an Abstract class as a property for a MATLAB class, you must also specify a default value for the property which is a class that is derived from the abstract class you specified.

The code below demonstrates how the code you provided might be modified to accomplish this workflow.

classdef demoClass
  properties
    TestProperty matlab.mixin.Heterogeneous = rootClass
  end
  methods
    function obj = demoClass
      % constructor that does not affect the property
    end
  end
end
classdef rootClass < matlab.mixin.Heterogeneous
  methods
    function obj = rootClass
    end     
  end
end

And now you should be able to instantiate an instance of "demoClass":

>> demoClass
ans = 
  demoClass with properties
    TestProperty: [1×1 rootClass]

MATLAB: How to keep the SetMethod and GetMethod of the dynamic properties when saving and loading the class instance in MATLAB R2019a

You need to implement your own saveobj and loadobj. In the saveobj you convert your class instance into a struct and store some meta information about your dynamic properties. In the loadobj you convert the previously created struct back into your class instance. See the example below:

classdef myCls < dynamicprops
    properties
        Prop1
        Prop2
    end
    methods
        function s = saveobj(obj)
            s.Prop1 = obj.Prop1;
            s.Prop2 = obj.Prop2;
            dynPropNames = setdiff(properties(obj), {'Prop1' 'Prop2'});
            for i=numel(dynPropNames):-1:1
                p = findprop(obj, char(dynPropNames(i)));
                s.DynPropInfo(i).Name = p.Name;
                s.DynPropInfo(i).Value = obj.(p.Name);
                s.DynPropInfo(i).GetMethod = p.GetMethod;
                s.DynPropInfo(i).SetMethod = p.SetMethod;
            end
        end
    end
    methods(Static)
        function obj = loadobj(s)
            if isstruct(s)
                newObj = myCls;
                newObj.Prop1 = s.Prop1;
                newObj.Prop2 = s.Prop2;
                if isfield(s, 'DynPropInfo')
                    for i=1:numel(s.DynPropInfo)
                        p=addprop(newObj, s.DynPropInfo(i).Name);
                        p.SetMethod = s.DynPropInfo(i).SetMethod;
                        p.GetMethod = s.DynPropInfo(i).GetMethod;
                        newObj.(s.DynPropInfo(i).Name) = s.DynPropInfo(i).Value;
                    end
                end
                obj = newObj;
            else
                obj = s;
            end
        end
    end
end

Best Answer

Related Solutions

MATLAB: How to set object property to Abstract class

MATLAB: How to keep the SetMethod and GetMethod of the dynamic properties when saving and loading the class instance in MATLAB R2019a

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