Cannot convert double value 0.01 to a handle.Cannot convert double value 5 to a handle.

Can someone please explain me in detail what does these handles mean! As theere solution is different everytime. Please tell me about it

[James Tursa]

Please show us the code you are using and describe in more detail what you are trying to do.

[Taha Sajid]

Hi James, I am fairly new to MATLAB. I didn't get this error, but one of my friends did and then I saw that everytime when there is "cannot convert double value into handle" there is a different method to solve it. So I was just wondering if you could demonstrate that with the help of example and a little explanation. Thanks

[James Tursa]

I can't help unless I see the code. I could only make guesses as to what might be wrong.

Answer 1

[Walter Roberson]

format long g
fig = figure(1);
fig

fig = 
  Figure (1) with properties:

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

  Show all properties

class(fig)    %notice it is a handle

ans = 'matlab.ui.Figure'

fig.Number    %that has an associated integer

ans = 
     1

H1 = handle(1);  %what happens if we convert 1 to handle?
H1

H1 = 
  Figure (1) with properties:

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

  Show all properties

isvalid(H1)

ans = logical
   1

H1 == fig        %is it the same as the handle we generated

ans = logical
   1

H2 = handle(2);  %what happens if we convert 2 to handle when no figure 2 exists?
H2

H2 =

	handle

ishandle(H2)

ans = logical
   0

set(1, 'Visible', 'on')   %works, because there IS a handle associated with double 1
try
  set(2, 'Visible', 'on')   %fails, because there is NO handle associated with double 2
catch ME
    disp(ME)
end

  MException with properties:

    identifier: 'MATLAB:class:InvalidHandle'
       message: 'Invalid or deleted object.'
         cause: {}
         stack: [7×1 struct]
    Correction: []

H1(1) = 1         %what if we assign a double into an existing handle

H1 = 
  Figure (1) with properties:

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

  Show all properties

try
  H1(2) = 2         %and if we try with a number that does not represent a handle?
catch ME
    disp(ME)
end

  MException with properties:

    identifier: 'MATLAB:graphics:CannotConvertDoubleToHandle'
       message: 'Cannot convert double value 2 to a handle'
         cause: {}
         stack: [7×1 struct]
    Correction: []

Historically, graphics objects were represented to the user as double, and it was valid to do things like

L1 = zeros(1,3)

L1 = 1×3

0 0 0

L1(1) = plot(rand(1,3))       %this still works!

L1 = 1×3

0.0048828125 0 0

and contrawise it was valid to do things like

L2 = plot(rand(1,4))

L2 = 
  Line with properties:

              Color: [0 0.447 0.741]
          LineStyle: '-'
          LineWidth: 0.5
             Marker: 'none'
         MarkerSize: 6
    MarkerFaceColor: 'none'
              XData: [1 2 3 4]
              YData: [0.658017094644957 0.881416534115599 0.405806040040171 0.216775714080096]
              ZData: [1×0 double]

  Show all properties

try
  L2(2) = 0.5
catch ME
    disp(ME)
end

  MException with properties:

    identifier: 'MATLAB:graphics:CannotConvertDoubleToHandle'
       message: 'Cannot convert double value 0.5 to a handle'
         cause: {}
         stack: [7×1 struct]
    Correction: []

and you can still do

L2 = double(plot(rand(1,3)))

L2 = 
           0.0050048828125

L2(2) = 0.5

L2 = 1×2

0.0050048828125 0.5

Thus, the particular error comes about in old code that happened to assign a graphics object to a variable thinking that graphics objects are represented by doubles (which they used to be), and then assigns a double (not intended to be a graphics object) into the same array.

You can work around this kind of problem by carefully using double() and handle(), but it is usually best to separate out the graphics objects from the non-objects.