What is best practice to determine if input is a figure or axes handle?

I've been confused about MATLAB graphics since change to the new graphics system. I do not know how I can check for a variable being a handle to a figure or axes. Functions that come to mind are:

ishandle
isgraphics
ishghandle
isa(x,'matlab.ui.Figure') % x being the variable representing a Figure or Axes
isa(x,'matlab.graphics.axis.Axes') % wow, these really are cumbersome commands!
% etc.

What are best practices to ensure maximal compatibility with most MATLAB versions to detect what kind of input I'm dealing with? Why are there no

isfigure

or

isaxes

functions built-in?

[Steven Lord]

Can you say a little more about what you're doing where you need to distinguish the two? One use case I can think of where you need to distinguish is if you want to know the figure that contains the object whose handle you have (which would be itself if you have a figure handle.) In that case you could use the ancestor function.

f = figure;
ax = axes('Parent', f);
parentFigure1 = ancestor(f, 'figure');
parentFigure2 = ancestor(ax, 'figure');

If you try to ask for the axes ancestor of a figure, you'll receive an empty array.

parentAxes1 = ancestor(f, 'axes');

[Erik]

ancestor is a nice function I didn't know about yet. Thanks. However, it's not exactly what I'm looking for.

I'm simply looking for the best way to determine if a variable is an (array of) axes or figure handle(s). isgraphics seems to detect valid graphics handles, but then what is the best way to determine the object being axes or figure(s)?

It seems tedious to check using either

isa(obj,'matlab.graphics.axis.Axes')
strcmp(obj.Type,'axes')
isa(obj,'matlab.ui.Figure')
strcmp(obj.Type,'figure')

Because there are multiple options, I asked my question: what's the best/most reliable/most compatible way to detect the object I'm dealing with? Should I look at the 'Type' property? Should I look at the class? Why aren't there isfigure or isaxes functions?

[Adam]

I use a test on the class in the new system, though usually I am doing it for validation so I use:

validateattributes( hAxes, { 'matlab.graphics.axis.Axes' }, { 'scalar' } )

which I wrapped up with another command in my own validateAxes( hAxes ) function. To return a boolean though I would just wrap the isa test in my own isAxes( hAxes ) function so that the ugly code is hidden under an intuitively named function.

I do also tend to get mixed up as to the difference between ishghandle and isgraphics for a more generic test though.

[adams13]

If you are talking about compatibility than I would use a method that works also in Octave:

function isAxes = IsAxes(ax)
try
    isAxes = strcmp(get(ax, 'type'), 'axes');
catch
    isAxes = false;
end
end

Answer 1

[Bjorn Gustavsson]

Simples, write those functions yourself, something along the lines:

function OK = isfigure(h)

if strcmp(get(h,'type'),'figure')
  OK = 1;
else
  OK = 0;
end

You could decorate your code to handle array input, do error checking and make the output proper Boolean output but the core part is to look at the type field of the graphics handle.

HTH

[Guillaume]

Well, if you're going to write your own test function, at least make it so it also works with arrays of handles:

function tf = isfigure(h)
   tf = strcmp(get(h, 'type'), 'figure');
end

[Adam Danz]

Like the other two answers here, this method also doesn't distinguish between a figure handle of class 'matlab.ui.Figure' and a double precision integer that happens to have the same value as a figure number ( I provided examples below the other two answers ). This becomes an issue in the case of a function with a variable number of input arguments (varargin) where an input could be a figure handle or an integer that has the same value as a figure number.

To make that distinction in r2014b and later, check the class of the variable as well.

 tf = strcmp(get(h, 'type'), 'figure') & isa(h, 'matlab.ui.Figure');

Answer 2

[Erik]

Another option I found inside the undocumented axescheck function is the specification of a type to check for when using isgraphics. The following function does the job for figures.

function tf = isfigure(f)
tf = isgraphics(f,'figure')

I didn't know isgraphics accepted the type to check for. This also works for 'axes'.

[per isakson]

isgraphics was introduced in R2014b

[Adam Danz]

Take note that isgraphics() doesn't distinguish between a figure handle of class 'matlab.ui.Figure' and a double precision integer that happens to have the same value as a figure number (for backward compatibility prior to r2014b).

close all
fig = figure();  %assigned fig 1
isfig = isgraphics(fig,'figure')

isfig = logical
   1

isfig = isgraphics(1,'figure')

isfig = logical
   1

This is because

handle(1)

ans = 
  Figure (1) with properties:

      Number: 1
        Name: ''
       Color: [1 1 1]
    Position: [509 657 583 437]
       Units: 'pixels'

  Show all properties

To accept only figure handles and not matching integers from r2014b and later,

close all
fig = figure();  %assigned fig 1
isfig = isgraphics(fig,'figure') && isa(fig,'matlab.ui.Figure')

isfig = logical
   1

isfig = isgraphics(1,'figure') && isa(1,'matlab.ui.Figure')

isfig = logical
   0

Answer 3

[PepijnB]

In the 'eyediagram'-function (build-in Matlab function), Mathworks checks the validity of a handle by the code:

ishghandle(h,'figure')

To check whether the handle is from an axes, use the following:

ishghandle(h, 'axes')

[Jordan Mandel]

This is a pretty remarkable find because it seems that this functionality is undocumented.

[Adam]

It's documented in R2019a. Don't know about earlier versions.

[Adam Danz]

I checked the archive and didn't find documentation for the 2nd input in r19a.

Note that ishghandle() doesn't distinguish between a figure handle of class matlab.ui.Figure and a double precision integer that happens to have the same value as a figure number (for backward compatibility prior to r2014b).

For example,

close all
fig = figure();  %assigned fig 1
isfig = ishghandle(fig,'figure')

isfig = logical
   1

isfig = ishghandle(1,'figure')

isfig = logical
   1

This is because

handle(1)

ans = 
  Figure (1) with properties:

      Number: 1
        Name: ''
       Color: [1 1 1]
    Position: [509 657 583 437]
       Units: 'pixels'

  Show all properties

To accept only figure handles and not matching integers from r2014b and later,

isfig = ishghandle(fig,'figure') && isa(fig,'matlab.ui.Figure')

isfig = logical
   1

isfig = ishghandle(1,'figure') && isa(1,'matlab.ui.Figure')

isfig = logical
   0

Answer 4

[Adam Danz]

I find myself revisiting this page from time to time and wanted to share an alternative best practice to determine if an array of inputs are figures or axes. It's based on Erik's solution using isgraphics(h,type) which is documented at least as far back as r2015b and functions in even older releases but with two differences:

1. Distinguishes between figure or axes handles and double precision values that match handle values, after r2014a. For example, close all; h=figure; isgraphics(1,'figure') returns true which could be problematic in some contexts after r14a.
2. Includes polaraxes for the is-axes test

Tested in r2020b & r2014a after removing features in the demo that didn't exist then.

% h is an array; function return a logical array the same size as h.  
isfigure = @(h)isgraphics(h,'figure') & (verLessThan('matlab','8.4') | ~isa(h,'double'));
isaxes = @(h)(isgraphics(h,'axes') | isgraphics(h,'polaraxes')) & (verLessThan('matlab','8.4') | ~isa(h,'double'));

Demo:

% 5 figures and 5 axes
close all
vis = 'off'; 
h(1) = figure('Visible',vis); % Visibility not needed for the demo
h(2) = figure('Visible',vis); 
h(3) = figure('Visible',vis);
h(4) = uifigure('Visible',vis); 
h(5) = uifigure('Visible',vis); 

h(6) = axes(h(1)); 
h(7) = polaraxes(h(2)); 
h(8) = subplot(2,2,1,'Parent',h(3));
h(9) = uiaxes(h(4)); 
tlo = tiledlayout(h(5),1,2);
h(10) = nexttile(tlo);
cleanup = onCleanup(@()delete(h));

isfig = isfigure(h)
%     isfig =
%       1×10 logical array
%        1   1   1   1   1   0   0   0   0   0

isax = isaxes(h)
%     isax =
%       1×10 logical array
%        0   0   0   0   0   1   1   1   1   1

This method correctly rejects double precision values that match the figure and axis handles when converted to double (>r14a):

val = double(h(1:3))
%   val =
%        1  2  3
isfig = isfigure(val)
%     isfig =
%       1×3 logical array
%        0   0   0

If you are intentionally using the double precision version of graphics handles after r2014a you can either remove those conditions from the functions or convert to handles in the inputs,

isfig = isfigure(handle(val))
%     isfig =
%       1×3 logical array
%        1   1   1