I created an object in MATLAB by using my own class my_class like this
car = my_class();
with
classdef my_class < handle
properties
color = 'red';
end
methods
function obj = my_class()
% ...
end
end
end
Now I am trying to find my object by its class (my_class) or by properties (color). But findall or findobj always return an empty matrix, whatever I am doing. Do you have any clue? Thanks.
EDIT I need something like this:
car1 = my_classA();
car2 = my_classA();
house1 = my_classB(); ... house25 = my_classB();
tree1 = my_classC(); ... tree250 = my_classC();
In my code, I can not refer to the names of the handles (like car2.color), because I have many different objects and I want to search for them by a function, that looks like the following one:
loop over all objects (maybe with findobj/findall without knowing object name/handle)
if object is of class `my_classA`
get handle of `my_classA`
change `color`
else if object is of class `my_classB`
get handle of `my_classB`
do something ...
end
end
I think you just want this:
% Create example array of objects
A(20) = object;
[A([3 14 17]).color] = deal('blue');
% Get those objects which are red, and change to orange
[A(strcmp({A.color}, 'red')).color] = deal('orange');
I have to admit, findobj would have been much better to read. But that only works on graphics handles as far as I'm aware, so you'd have to overload it for your class.
And that overloaded function, would contain something similar to this.
EDIT as noted by Navan, this works:
B = findobj(A, 'color', 'red');
[B.color] = deal('orange');
seems to be faster than the strcmp method, too.
Related
I have an object apple created by my own class in MATLAB:
apple = classA();
The class looks like this:
classdef classA < handle
properties
color = 'red';
end
methods
function obj = classA()
% ...
end
end
end
The question: How do I get the object or handle pointer of apple? I want to search for objects by their properties, like:
isprop(eval(mat(i).name),'color')
with mat = whos. So I need to get the pointer of the object, represented by the struct mat(i).name. I just need the reference, not a copy of the desired object. The purpose is this:
If I get the pointer somehow, like
ptr_to_apple_object = get_pointer_fct( mat(i).name )
then I am able to change the properties of the apple-object like:
ptr_to_apple_object. color = 'yellow'
Do you have any ideas? Thanks.
There's really no good way to find all current objects of a particular class, but you could use whos to get a struct about all variables, loop through this and determine which ones have the property you and then modify
variables = whos;
for k = 1:numel(variables)
obj = eval(variables(k).name);
if isobject(obj) && isprop(obj, 'color')
obj.color = 'yellow';
end
end
If you're looking for a specific class, you can use the class field of the output of whos
is_class = ismember({variables.class}, 'classA');
instances = variables(is_class);
for k = 1:numel(instances)
obj = eval(instances(k).name);
obj.color = 'yellow';
end
Update
Since you are subclassing handle, when you assign your instance to a new variable (obj = val(variables(k).name) above), it does not create a copy of your instance, but rather a new reference to the same object.
b = classA;
c = b;
b.color = 'red';
c.color
% 'red'
On MATLAB R2014b, when you have a struct (or custom class) having a field that is a scalar categorical, when displaying the struct it will show [1x1 categorical] instead of what I want to achieve as shown below.
MWE:
struct.field = categorical({'category'})
Output:
struct =
field: [1x1 categorical]
My desired output:
struct =
field: category
or:
struct =
field: category [1x1 categorical]
I want this, because I'm writing some classes that have a categorical property that is always scalar; because I know this by definition, I don't need the objects' category to be displayed as [1x1 categorical]. When displaying the custom objects, I'd like it to show the category instead.
I could overload disp in my class methods, but then I'd need to rewrite a lot of displaying code from disp itself instead of merely changing the way a scalar categorical in a struct field shows.
Any ideas on how to achieve this? If your answer involves overloading disp in the class definition, then I want to see how you could display the object's other properties like a normal disp(obj) would, in addition to displaying the categorical property the way I want. Any ideas or thoughts you have might help me write my own answer, so please share any.
After playing around with this for a while, I think I finally have something that works for displaying these scalar categorical values within a custom class.
The basic idea is that I overload the get method for the property that is holding the categorical. I can then check the call stack to see what is trying to get the value of the variable. If it's our overloaded disp method (which is called any time we want to display our class), then I return the category name if it's only a scalar categorical. Otherwise, I return the value of the property itself (as a categorical).
It's definitely not the most elegant due to it's reliance on dbstack but it seems to work quite well.
classdef categoryclass < handle
properties
a = categorical({'category'});
end
methods
% Get Method for "a" property
function res = get.a(self)
% Get the call stack to determine *what* called this
stack = dbstack();
methodname = sprintf('%s.disp', class(self));
% If it is a scalar and it was called by our overloaded display
% method, then return the category name
if isscalar(self.a) && isa(self.a, 'categorical') && ...
strcmp(methodname, stack(end).name)
res = categories(self.a);
res = res{1};
% Otherwise return just the value itself
else
res = self.a;
end
end
% This ensure that disp() shows up in the stack
function disp(self)
% Simply call the built-in display function
builtin('disp', self);
end
end
end
Now if we try this out.
cls = categoryclass()
categoryclass with properties:
a: 'category'
Check that when we request the value we actually get a categorical.
class(cls.a)
ans =
categorical
Now change the value of it.
cls.a = categorical({'another category'})
categoryclass with properties:
a: 'another category'
Now use two categories
cls.a = categorical({'one', 'two'})
categoryclass with properties:
a: [1x2 categorical]
NOTE: This only appears to be an issue in R2014b and R2015a. It was fixed in all later releases.
It's been a while, but today I needed this again. I thought of another way to display scalar categorical variables. The following example class does the trick.
classdef dispfmtTest < matlab.mixin.Copyable
properties
prop = categorical(1) % default value is a scalar categorical
end
methods
function dispfmt(obj) % dispfmtTest object to display format
obj.prop = char(obj.prop); % convert to char type
end
function disp(self)
obj = copy(self); % copy is provided by superclass
dispfmt(obj)
disp#matlab.mixin.Copyable(obj) % call superclass disp
delete(obj)
end
end
end
The dispfmtTest class is a subclass of matlab.mixin.Copyable, which is in turn a subclass of handle. It provides the copy method to the disfmtTest class, which is used to temporarily create a copy of which the value of property prop is changed to whatever desired display format in method dispfmt. Then, the modified copy of the object is displayed using the regular disp function as provided by matlab.mixin.Copyable.
Demo
Running obj = dispfmtTest yields
d =
dispfmtTest with properties:
prop: '1'
and class(d.prop) yields
ans =
categorical
This is the behaviour as I expected. Support for array properties can be achieved too using isscalar.
We have this code in 'Reconstruction the subclass object from a saved struct' from MATLAB OOP documentation.
classdef MySuper
% Superclass definition
properties
X
Y
end
methods
function S = saveobj(obj)
% Save property values in struct
% Return struct for save function to write to MAT-file
S.PointX = obj.X;
S.PointY = obj.Y;
end
function obj = reload(obj,S)
% Method used to assign values from struct to properties
% Called by loadobj and subclass
obj.X = S.PointX;
obj.Y = S.PointY;
end
end
methods (Static)
function obj = loadobj(S)
% Constructs a MySuper object
% loadobj used when a superclass object is saved directly
% Calls reload to assign property values retrived from struct
% loadobj must be Static so it can be called without object
obj = MySuper;
obj = reload(obj,S);
end
end
end
I have a question about obj = MySuper. What is purpose of this line? How we can call MySuper object from this function without insert any object to loadobj function?
You first question is: What is the purpose of the obj = MySuper; line?
The answer is that the obj = MySuper; line initiates the variable obj as an element of the class MySuper. Non-static functions in a class will only run if the first input parameter is an instance of the class, so if obj is not initiated as a MySuper-object, then matlab will look for other functions called reload to run, and if none is found give you an error.
For your second question, I am not 100% sure what you mean. But I hope one of the following points will answer your question:
If you want to make a function that relates to a class, but not to a specific instance of the class, you can make a static function, these can take any input (also (if you want it that way) no input at all) - that is they don't need to have a first input parameter of the specific class.
To run a static function, use the class name followed by a dot and then the function name, so here you would type MySuper.loadobj(S) to run the function with the parameter S.
I would suggest that you try this out with the given example to better get to know the way oop works in matlab, you may for example try:
S.PointX = 1;
S.PointY = 2;
obj = MySuper.loadobj(S)
I hope this answers your questions.
I am trying to implement save/load functions in a MATLAB (R2009a) UI. My object implements a layout function that generates a user interface for the object. I am trying to implement the callbacks for the save/load buttons. The save button works and save the object out to a MAT file which can be loaded later.
My problem is implementing the callback for the load button. I cannot seem to get the load to load the data from the MAT file and update the properties of the new object. Any suggestions on where I am going wrong along with suggestions on how I might proceed is greatly appreciated.
The important code is my class definition file of course my actual object implements many more properties and methods but here is a skeleton of what I have
classdef myObj<handle
properties
image % property holds a matlab image matrix
objCount % number of objects in image
end
properties(Transient=true)
parent
children
end
methods
function myObj
% empty constructor
end
function load_object(self)
% ask user for file
[fileName, pathToFile]=uigetfile('*.mat','Select .mat file');
tmp = load(fullfile(pathToFile,fileName);
if isfield(tmp,'obj')
self = tmp.obj;
end
end
LayoutFcn(self) % UI layout function
end
end
The UI layout is defined in a seperate file LayoutFcn.m which basically looks like
function LayoutFcn(self)
% create figure window and add various UI elements
...
% create load button
self.children(end+1) = uipushtool('Parent',hToolbar, ... % set parent to current toolbar
'CData',iconRead('open-document.png'), ... % read icon image from file
'Tag','uiLoad', ...
'ClickedCallback',#(hObj,event)loadingMyObject(self,hObj,event));
% create save button
self.children(end+1) = uipushtool('Parent',hToolbar, ... % set parent to current toolbar
'CData',iconRead('save-document.png'), ... % read icon image from file
'Tag','uiSave', ...
'ClickedCallback',#(hObj,event)savingMyObject(self,hObj,event));
...
end
function loadingMyObject(self,hObj,event)
self.load_object; % call load_object method defined above in class definition
end
function savingMyObject(self,hObj,event)
[fileName,pathName]=uiputfile('.mat','Save object to MAT file');
obj = self;
save(fullfile(pahtName,fileName),'obj')
end
Note: I am using MATLAB R2009a.
The code doesn't throw any errors. The way I wrote the code the parent object (represented by self) does not get updated after the call to LOAD in the method load_object. SO, this has the desired effect:
>> var = myObj;
>> var.load_object;
However, if I use the loadingMyObject callback defined in LayoutFcn.m in this fashion
>> var = myObjl
>> var.LayoutFcn
-> click Load button to call _loadingMyObject_
doesn't affect var properties. That is var will still have its default property values after clicking the Load button.
Changing the load methods to use set as suggested by gnovice throws the following error
??? Error using ==> set
Conversion to double from FujiCalibration is not possible.
even though I have set/get methods for each property; as in
method set.image(self,II)
% ... some data validation code ...
self.image = II
end
Using a loop to set each field as suggested by Mr Fooz is not really an option as my full class has public constant that throw an error when they are set.
I am looking for a solution that would avoid me having to hand code setting each field individually. Although at this point it seems like the only possibility.
I believe Mr Fooz is right. The self variable passed to load_object is an object of type "myObj", but the line:
self = tmp.obj;
is simply overwriting the self variable with the structure stored in tmp.obj. Doing:
self.image = tmp.obj.image;
should instead invoke a set operator for the image property of object self. In the MATLAB documentation there is a sample class definition with a method called "set.OfficeNumber" that illustrates this.
In addition, the following line in your function savingMyObject may be unnecessary:
obj = self;
I think it might make most sense (and make the code a little clearer) if you used the name "obj" in place of the word "self" within your class code (as the documentation tends to do). "self" doesn't appear to be any kind of special keyword in MATLAB (like it may be in other languages). It's just another variable as far as I can tell. =)
EDIT #1:
If the prospect of having to set each property individually in your load_object method doesn't sound like fun, one way around it is if you have a SET method for your object that is designed like the SET method for handle graphics. That SET command can accept a structure input where each field name is a property name and each field value is the new value for that property. Then you would have one call like:
set(self,tmp.obj);
Quite a bit shorter, especially if you have lots of properties to set. Of course, you'd then have to write the new SET method for your object, but the shortened syntax may be worth the extra work if it comes in handy elsewhere too. =)
EDIT #2:
You may be able to use the loop Mr Fooz suggested in conjunction with a try/catch block:
fn = fieldnames(tmp.obj);
for i = 1:numel(fn),
try
self.(fn{i}) = tmp.obj.(fn{i});
catch
% Throw a warning here, or potentially just do nothing.
end
end
Don't assign values to self. All that does is replace the binding to the self variable in the scope of the method call. It does not call a magical copy constructor to replace the object reference in the caller. Instead, copy the fields into self. Try something like:
if isfield(tmp,'obj')
self.image = tmp.obj.image;
self.objCount = tmp.obj.objCount;
end
Combining Mr Fooz's and gnovice's suggestions, I added a SET function with the following definition
function set(self,varargin)
if isa(varargin{1},'FujiCalibration')
tmp = varargin{1};
fns = fieldnames(self);
for i = 1:length(fns)
if strcmpi(fns{i}(1:2),'p_')
self.(fns{i}) = tmp.(fns{i});
end
end
self.calibImage = tmp.calibImage;
else
proplist=fields(self);
for n=1:2:length(varargin)
tmp = proplist(strcmpi(proplist,varargin{n}));
value = varargin{n+1};
switch length(tmp)
case 0
msg = char(strcat('There is no ''', varargin{n}, '''property'));
error('FujiCalibration:setPropertyChk',msg)
case 1
tmp = char(tmp);
self.(tmp) = value;
end
end
end
end
I then modified the load_object method as suggested by gnovice by changing
self = tmp.obj
to
set(self,tmp.obj).
I need to make sure that properties with values I want to persist are prefixed with 'p_'.
Thanks to gnovice and Mr Fooz for their answers.
Is there a better way to implement copy construcor for matlab for a handle derived class other than adding a constructor with one input and explicitly copying its properties?
obj.property1 = from.property1;
obj.property2 = from.property2;
etc.
Thanks,
Dani
There is another easy way to create copies of handle objects by using matlab.mixin.Copyable. If you inherit from this class you will get a copy method which will copy all the properties for you.
classdef YourClass < matlab.mixin.Copyable
...
a = YourClass;
b = copy(a); % b is a copy of a
This copy method creates a copy without calling constructors or set functions of properties. So this should be faster. You can also customize the copy behavior by overriding some methods.
If you want a quick-and-dirty solution that assumes all properties can be copied, take a look at the PROPERTIES function. Here's an example of a class that automatically copies all properties:
classdef Foo < handle
properties
a = 1;
end
methods
function F=Foo(rhs)
if nargin==0
% default constructor
F.a = rand(1);
else
% copy constructor
fns = properties(rhs);
for i=1:length(fns)
F.(fns{i}) = rhs.(fns{i});
end
end
end
end
end
and some test code:
f = Foo(); [f.a Foo(f).a] % should print 2 floats with the same value.
You can even use
try
F.(fns{i}) = rhs.(fns{i});
end
which makes the method more useful