The property postSet of MATLAB handle classes are very handy, however I would be happy to be able to trigger nested classes separately. A minimal example with two nested classes for illustration:
classdef parentClass < handle
properties (SetObservable = true)
childClass
end
methods
function this = parentClass()
this.childClass = childClass();
end
end
end
and
classdef childClass < handle
properties (SetObservable = true)
value
end
methods
function this = childClass()
this.value = 0;
end
end
end
In the example script "runTest"
p = parentClass();
addlistener(p.childClass,'value','PostSet',#(o,e)disp('child value set'));
addlistener(p,'childClass','PostSet',#(o,e)disp('parent value set'));
p.childClass.value = 1;
The result is (as expected)
>> runTest
child value set
However, I am looking for an elegant way to detect the property change on both levels such that the result would be:
>> runTest
child value set
parent value set
One way to do this is to use the fact that the PostSet event gets triggered by default even when the previous and current values are the same. In the constructor of parentClass, we add a listener to the childClass's PostSet event, and the event handler only reassigns the childClass object:
classdef parentClass < handle
properties (SetObservable = true)
childClass
end
methods
function this = parentClass()
this.childClass = childClass();
addlistener(this.childClass,'value','PostSet', #this.handlePropEvent);
end
function handlePropEvent(this, src, event)
this.childClass = this.childClass;
end
end
end
Note that you would want to be more careful implementing this so that the event listener gets adequately disposed of (and reassigned) if the childClass property is assigned a different object.
In practice, childClass should probably implement its own event type which gets triggered by all property changes you're interested in, and parentClass only listens to that event.
Related
I am working with a custom defined class I called "PathObj_Standard". I want to make sure that when I load this class, if the property CalcDate was saved as a cell array it is converted to a standard array. However, I changed the class definition some time ago, so when I use the loadobj function, I am getting a struct instead of an object. The original code I'm using has a lot more properties, so I'd rather not create a new object by assigning property by property from the struct to a new object. Furthermore, I'm also hesitant to change the constructor to accept a struct as an argument.
I tried using the class function inside loadobj, but I am getting a Cannot redefine class 'PathObj_Standard' without a call to 'clear classes' error. Isn't this function supposed to force conversion of a struct to an object? Why doesn't it work within the loadobj function?
classdef PathObj_Standard < handle
properties (SetAccess = protected)
CalcDate;
Name;
end
methods(Static)
function obj=loadobj(s)
if isstruct(s)
obj=class(s,'PathObj_Standard');
else
obj=s;
end
if not(isempty(obj.CalcDate)) && iscell(obj.CalcDate)
obj.CalcDate=cell2mat(obj.CalcDate);
end
end
end
methods
function obj=PathObj_Standard(Name,CalcDate)
obj.Name=Name;
obj.CalcDate=CalcDate;
end
end
The issue is that calling class attempts to create a class which you can't do from within your loadobj. You'll want to call the actual constructor
Also in my experience, the easiest way to construct a class from a struct is to inherit from hgsetget rather than handle as that automatically has the set and get methods of MATLAB's graphics objects and these methods can accept property/values in the form of a struct. In newer versions of MATLAB, you can also use the SetGet mixin
classdef PathObj_Standard < hgsetget
If you do this, you could change your loadobj method to be something like
function obj = loadobj(s)
% Update the input struct as needed
if isfield(s, 'CalcDate') && ~isempty(s.CalcDate) && iscell(s.CalcDate)
s.CalcDate = cell2mat(s.CalcDate);
end
% Call the default constructor
obj = PathObj_Standard();
% Update all properties that were supplied to loadobj
set(obj, s)
end
I have an object from my own class object that inherits from my own class data and my own class graphic in MATLAB. To represent the object object, it uses properties and methods from the data-superclass. Now I want to draw my object object with methods from the graphic-superclass, but the methods in this superclass don't know anything about its object-subclass.
Is there a way to give the required data, that is stored in the object-subclass, to the graphic-superclass without putting this information into a function argument like object.draw(this_data_stuff) with the method drawfrom the graphic-superclass and the data this_data_stuff from the object-subclass?
The only way I figured out is to store the subclass object object as property in the graphic-superclass, but it seems odd to store a subclass-object as property in a superclass-object, while the subclass inherits from the same superclass.
EDIT:
data-class:
classdef data < handle
properties
data_stuff
end
methods
function obj = data
end
function obj = compute(obj)
obj.data_stuff = ... % math
end
end
end
graphic-class:
classdef graphic < handle
properties
end
methods
function obj = graphic
end
function obj = draw(obj)
plot(obj.data_stuff,t) % ERROR, property 'data_stuff' is unknown
end
end
end
object-class:
classdef object < data & graphic
properties
end
methods
function obj = object
end
end
end
Test:
object_A = object; % creates object
object_A.compute; % generates data_stuff
object_A.draw; % draws data_stuff, Error here, because 'draw` needs access to the 'data_stuff'-property.
I'm trying to change a property in a class called houses via a utility method which is Static. I'm getting terribly confused with the reference obj as I don't know when and where it should be used. I am trying to bypass the constructor method so I can access the setProperty method, but I am getting errors such as too many output arguments. I've tried passing in obj as well as x, but I get similar errors. However, I can change the property a if I pass in a value to the constructor method.
classdef houses
properties
a;
end
methods
% constructor method
function obj = houses()
end
end
methods (Static)
function setProperty(x)
obj.a = x;
end
end
end
In general, you should not use static methods to set properties of a class. If your property is public, then you can use a static method but it is highly recommended that you do not. If your property is private/protected, then you definitely cannot use a static method to modify it.
Your class should look like this then (I took the liberty of stating explicitly the access properties of each block):
classdef houses
properties (Access = private)
a;
end
methods (Access = public)
% constructor method
function obj = houses()
end
function SetA(obj, a)
obj.a = a;
end
function DoSomething(obj, more_parameters)
% Lengthy stuff here
end
end
end
Now, regarding your question about obj: the answer is you must pass obj as the first argument of every instance method. The variable obj refers to the current instance of the class in a generic way. See for example the method DoSomething.
Static methods do not have access to any of the properties of the class, unless public. As such, when declaring a static method, you should not pass the obj variable.
Last thing: always use explicit access modifiers for your properties and methods. It will save you some headaches.
A static method is not typically supposed to access an object (hence it does not have access to obj).
If you want to modify a static propperty (shared by all objects, and the class itself), you can use something like:
classdef houses
properties (Static)
a;
end
methods
% constructor method
function obj = houses()
end
end
methods (Static)
function setProperty(x)
houses.a = x;
end
end
end
Regarding obj, it is the 1st argument of every methods (non static). So when you do:
o = myClass();
o.myMethod(args);
Matlab will see this as:
myMethod(o, args);
So when you define the method, you have to put obj as the 1st argument (in fact you can choose any name, it does not have to be obj).
I want to change the value of a property in a Matlab class from a function within the same matlab class. I.e on of the functions in the class is generating a value that I want to assign to a property for that class.
This is the properties of the class:
classdef myclass < handle
properties (SetAccess = public)
notional;
T;
u;
nbrAnnualPayments;
sigma_u;
sigma_s;
s_i;
N2;
cash_flow;
paymentDates;
detTP;
volTP;
..... and this is the set method.
function set.detTP(obj,value)
if ~(value > 0)
error('Property value must be positive')
else
obj.detTP = value;
end
end
Now I want to write something like:
obj.set.detTP(obj, value);
From another function to update the value of the detTP property.
How should i do this? How should the set function be written (i.e. is it written correctly now)? and how should the syntax look like for assigning the new value to the property.
Thanks in advance for your help!
You can simply write
obj.detTP = value;
or, if you'd use hgsetget instead of handle as the base-class, you could do
set(obj, 'detTP', value);
Your set-method looks fine at first sight.
Using Matlab R2012a, I have the following class hierarchy:
classdef Parent < handle
properties (Abstract, SetAccess = protected)
Limit
end
end
classdef SimpleChild < Parent
properties (SetAccess = protected)
Limit = 1.0
end
end
classdef ExtendedChild < Parent
properties (Access = private)
Child = SimpleChild
end
properties (Dependent, SetAccess = protected)
Limit
end
methods
function this = ExtendedChild
this.Limit = 2;
end
function output = get.Limit(this)
output = this.Child.Limit;
end
function set.Limit(this,input)
this.Child.Limit = input;
end
end
end
This a simple example where the "Parent" class defines an abstract "Limit" property, which is implemented in both the "SimpleChild" and the "ExtendedChild" class. The "ExtendedChild" class encapsulates a private instance on the "SimpleChild" class and forward the access methods (get/set) to the private instance. Constructing an "ExtendedChild" instance fails with the following message:
>> obj = ExtendedChild
Setting the 'Limit' property of the 'SimpleChild' class is not allowed.
Error in ExtendedChild/set.Limit (line 16)
this.Child.Limit = input;
Error in ExtendedChild (line 10)
this.Limit = 2;
I would have expected the "Limit" property to be settable since it is defined in the "Parent" class with a protected SetAccess. I can make the problem disappear if the property is implemented directly in the "Parent" class, but then I cannot redefine it as dependent in the "ExtendedChild" class, which is the point of the construction (separation of interface and implementation).
Can someone tell me if I'm doing something wrong?
Since the Limit property of SimpleChild is protected, you can only set its value from SimpleChild or a subclass of SimpleChild, which is not the case for ExtendedChild.
I'm not entirely sure what you're trying to achieve, so can't really advise on what the "best" way to do it might be. But I would guess that whatever you want, it's unlikely that having a set method for a Dependent property is the right way to achieve it - there are only very rare reasons why you might want to do that.