Matlab Error : Function is not defined for 'matlab.ui.Figure' inputs.

Function is not defined for 'matlab.ui.Figure' inputs.   OTL....

Graphics Functions Return Objects, not Numeric Handles

I mentioned this briefly in Part 2 of this series. Graphics functions now return objects, not numeric handles. The R2014b documentation has detailed information about this subject in the section called Graphics Handles Are Now Objects, Not Doubles. I will give a couple of simple examples to illustrate what can happen with code written before R2014b.

Prior to R2014b, you could store a set of handles to graphics objects in an array and then add some numeric data to that array. In R2014b, that will cause an error.

x = -pi:0.1:pi ;
y1 = sin(x);
y2 = cos(x);
myLines = plot(x,y1,x,y2)    % plot returns an array of two Line objects

If you then try to set myLines(3) = 1.2, you get the following error.

  Cannot convert double value 1.2 to a handle

MATLAB won't let you add numeric values to an array of graphics objects. A similar problem occurs if you try to use an object handle in a function where MATLAB expects a numeric value. A simple example of this happens with the sprintf function.

a = sprintf('You clicked on figure %d\n', gcf);

The %d specification in the sprintf format string expects an integer value. However, since gcf is a figure object, you get the following error.

  Error using sprintf
  Function is not defined for 'matlab.ui.Figure' inputs.

Here is one final example. Because graphics handles used to be numbers, you could use them in logical expressions.

if (get(0, 'CurrentFigure'))
  disp(['Figure ' get(gcf, 'Name')'])    % display the figure name for gcf
else
  disp('No open figures')                % there is no open figure
end

This worked in earlier versions of MATLAB because get(0,'CurrentFigure') would return either an empty array or a numeric figure handle. Both of these values are valid in the logical test of the if statement above. In R2014b, this will cause an error.

  Conversion to logical from matlab.ui.Figure is not possible.

We have tried to maintain compatibility with previous releases in some cases. For example, you can still use 0 to refer to the graphics root in functions like get and set. As a best practice, however, we now recommend using the groot function to get the graphics root. Similarly, we still support the use of literal integer values to refer to figures in functions like set, get, and figure. Again, the best practice is to use a variable which contains the object when using these functions.

If you find yourself really stuck, it is possible to cast object handles to numeric handles using the double function. You can then cast the number back to an object handle using the handle function. We don't recommend this as a long term solution. Be aware that we may choose to remove this feature in a future version of MATLAB. If we do, we'll let you know in advance.