Weird bug in App Designer: " Unrecognized function or variable 'DispNumb'. "

Hi, I'm using App Designer to create a GUI of a unit converter. There's 14 different converters, ranging from 'metres to feet', to 'Celsius to Fahrenheit', etc. In my App Designer I have a callback that responds to a Convert button being pushed after an input is made. In it are all my conversion calculators, that respond to a user-defined function 'answ = ConverterCore(inp, FromUnit)'. The first few lines are here (the .m file)...

function answ = ConverterCore(inp, FromUnit)

    if strcmp(FromUnit, 'C')
        answ = (inp*1.8)+32; %C to F
    elseif strcmp(FromUnit, 'F')
        answ = (inp-32)*(5/9); %F to C
        
    elseif strcmp(FromUnit, 'cm')        %Problem from here...
        answ = (inp/2.54); %cm to inch
    elseif strcmp(FromUnit, 'inches')
        answ = (inp*2.54); %inch to cm   %...to here

    elseif strcmp(FromUnit, 'metres')
        answ = (inp/0.3048); %m to ft
    .
    .
    .
    
    end
end

...and the part in my .mlapp file that calls them is here...

When I run the 'cm to inch' part or the 'inch to cm' part, I get this:

Unrecognized function or variable 'DispNumb'.

Error in Milestone_3_GUI/ConvertButtonPushed (line 117)
            app.HasbeenconvertedtoEditField.Value = (DispNumb);

(that's all red in my UDF), line 117 is here:

app.HasbeenconvertedtoEditField.Value = (DispNumb);

And remember this code works for all of my converters except for cm to inch and inch to cm, so it's bizarre!

Lastly, if this helps, here's the calls to my UDF for the same parts above:

% Button pushed function: ConvertButton
        function ConvertButtonPushed(app, event)
            value = app.FromtoDropDown.Value;
            if strcmp(value, 'Celsius to Fahrenheit')
                DispNumb = ConverterCore(app.ValueEditField_C.Value, 'C');
                app.UnitSign.Value = ('˚F');
            elseif strcmp(value, 'Fahrenheit to Celsius')
                DispNumb = ConverterCore(app.ValueEditField_F.Value, 'F');
                app.UnitSign.Value = ('˚C');
                
            elseif strcmp(value, 'Centimetres to Inches')
                DispNumb = ConverterCore(app.ValueEditField_DistnMass.Value, 'cm');
                app.UnitSign.Value = ('inches');
            elseif strcmp(value, 'Inches to Centimetres')
                DispNumb = ConverterCore(app.ValueEditField_DistnMass.Value, 'inches');
                app.UnitSign.Value = ('cm');
                
            elseif strcmp(value, 'Metres to Feet')
                DispNumb = ConverterCore(app.ValueEditField_DistnMass.Value, 'metres');
                .
                .
                .
            end
        end

I see no difference! I really need some guidance on what to do.

Cheers! Let me know if there's any lines I can give to clarify anything.

[Walter Roberson]

I predict that your dropdown uses Centimeters instead of Centimetres

[Simon T]

My dropdown is written as "cm". I searched "centimet" in my script and only found the two "centimetres" lines of code. Not it :(

[Adam Danz]

Always include a final 'else' to catch these types of errors. For example,

.
.
.
else
    error('Conversion ''%s'' not recognized.',value)
end    

Also, use strcmpi instead of strcmp unless you really need case sensitive matching.

Lastly, consider using a switch-case instead of a bunch of if-elseif conditions.

[Simon T]

Cheers Adam. That was definitely going to be the final 'else' catching that error. Just solved it a minute before you commented!

I'll need to look deeper into switch-case statements.

[Steven Lord]

Alternately instead of an if / elseif / else / end block or a switch / case / otherwise / end block you could create a cell array of function handles, one per element of your dropdown, where each function performs the appropriate conversion for that item in your dropdown. Use ismember to identify which element of the Items property is captured in the Value property and call the appropriate function handle from the cell array.

You would need to keep the Items of your dropdown list and the function handles in sync, but that's not much different from needing to keep the Items of your dropdown list and the elements in your if or switch statements in sync.

Answer 1

[Simon T]

Problem solved! I took a step back and checked it all again.

Found out that this part was the culprit:

elseif strcmp(value, 'Centimetres to Inches')
                DispNumb = ConverterCore(app.ValueEditField_DistnMass.Value, 'cm');
                app.UnitSign.Value = ('inches');
elseif strcmp(value, 'Inches to Centimetres')
                DispNumb = ConverterCore(app.ValueEditField_DistnMass.Value, 'inches');
                app.UnitSign.Value = ('cm');

In the menu that stored "value" as its selected dropdown, my converters were actually called "cm to Inches" and "Inches to cm", not "Centimetres to Inches" and "Inches to Centimetres", like in the code above. Walter's comment made me think that bit harder.