Code checking error in App Designer, it thinks xxxx.BackgroundColor is a scalar

I'm changing the background color to alert the user about various (async) conditions and button pressed.

            if  app.STOPTRIALSButton.BackgroundColor == [0.95 0.33 0.10]
              app.STOPTRIALSButton.BackgroundColor = [0 1 0]; 
            end

and I get the warning:

Unexpected use of '[' in a scalar context.

but of course colors are RGB three values, so the code runs fine.

Also while the Component browser shows (another) color as 0.65, 0.65, 0.65 that's the wrong syntax (no commas please for easier cut and paste) and in the startup code the values are actually [0.651 0.651 0.651] so my compare failed without significant research as to why.

Finally, App Designer isn't listed as a product below, so I can't flag that. Just saying MATLAB is the product.

Answer 1

[Voss]

To avoid the warning, use:

if isequal(app.STOPTRIALSButton.BackgroundColor,[0.95 0.33 0.10])
    app.STOPTRIALSButton.BackgroundColor = [0 1 0]; 
end

[Alessandro Livi]

except [0.95 0.33 0.10] doesn't work since even though those are the numbers given by the Component Browser, App Designer puts in code like this:

app.STOPTRIALSButton.BackgroundColor = [0.949 0.3294 0.102] so isequal doesn't work

(unless you can set an epsilon where isequal() is sloppy to 2 decimal rounding

Numeric inputs are equivalent if they are the same size and their contents are of equal value.

I know that converting from float to decimal strings is yucky so how about App Designer always rounding colors to 2 decimal places (or use 0-255 like everyone else does) since internally its really bytes anyway above color being 242 84 26

242/255 = 0.949 and 84/255 = 0.3294117647058824 if you look far enough it will never match

You could also go 0 to 100 (%) for those who don't like binary based numbers, lower precision but good enough. OR at least put a warning in the help about how to find equal colors.

searching equal colors is of no help.

[Walter Roberson]

Do not compare floating point numbers for exact equality.

if isnumeric(app.STOPTRIALSButton.BackgroundColor) && all(abs(app.STOPTRIALSButton.BackgroundColor - [0.95 0.33 0.10]) <= 0.01)

[Voss]

If App Designer puts a line of code that says

app.STOPTRIALSButton.BackgroundColor = [0.949 0.3294 0.102]

and you want to check that that BackgroundColor is still in effect, use

if isequal(app.STOPTRIALSButton.BackgroundColor,[0.949 0.3294 0.102])

Answer 2

[Alessandro Livi]

This is crazy that you can't simply compare colors, consder options I mention above meanwhie

if isnumeric(app.STOPTRIALSButton.BackgroundColor) && all(abs(app.STOPTRIALSButton.BackgroundColor - [0.95 0.33 0.10]) <= 0.01

should work,

(make this a documented (or included) function SameColor( Color1 Color2) as above?

Also I was directed to a colors names list (not in MatLab) and most of the names don't work.

'color name' must match a rather short list, none of the off white names work (like a name for [0.94 0.94 0.94] or [0.90 0.90 0.90] which seem to be common default background colors

[Voss]

Here's the list of named colors in MATLAB

https://www.mathworks.com/help/matlab/creating_plots/specify-plot-colors.html

They are the eight colors all of whose RGB components are 0 or 1 (i.e. [0,0,0], [0,0,1], [0,1,0], [0,1,1], [1,0,0], [1,0,1], [1,1,0], [1,1,1]).