Simple turn on Lamp with switch in app designer

I am trying to learn about app designer and have tried to make a basic app that turn the lamp GREEN if the switch is ON, and RED if the switch is OFF. For some reason there is no change in color of the lamp? I am using R2023a version of matlab.

function SwitchValueChanged(app, event)
        
        disp('SwitchValueChanged callback triggered'); % Confirm function call
        value = app.Switch.Value;     
        disp(['Switch value: ', value]); % Display switch value

        
        if strcmp(value, 'on')
            disp('Setting lamp color to green') % Debugging message
            set(app.Lamp,'Color','green')



        elseif strcmp(value, 'off')
            disp('Setting lamp color to red') % Debugging message
            set(app.Lamp,'Color','red')

        end
end

Answer 1

[Shivani]

Hello @keaton,

I am not able to reproduce the issue with the given code snippet, so I may not be able to provide the most accurate solution. However, upon analyzing the code snippet shared, it is my understanding that the property to set the color of a lamp is not directly set using `set(app.Lamp, 'Color', 'green')` as you would in traditional MATLAB GUI programming (using set/get with handles). Instead, you work directly with the property of the component.

You can refer to the following code snippet for an example on how this can be done:

function SwitchValueChanged(app, event)
disp('SwitchValueChanged callback triggered'); % Confirm function call
value = app.Switch.Value;     
disp(['Switch value: ', value]); % Display switch value

if strcmp(value, 'On') 
    disp('Setting lamp color to green') % Debugging message
    app.Lamp.Color = 'green'; % Directly set the Color property
    
elseif strcmp(value, 'Off')
    disp('Setting lamp color to red') % Debugging message
    app.Lamp.Color = 'red'; % Directly set the Color property
end

end

I referred to the following documentation to understand the implementation details of sharing data within App Designer: https://www.mathworks.com/help/matlab/creating_guis/share-data-across-callbacks-in-app-designer.html

Hope this helps!

Answer 2

[Adam Danz]

The problem is that the values the switch returns are On and Off with capital letters. Your string comparison is case sensitive so On (upper case O) does not match on (lower case o) and Off does not match off.

if strcmp(value, 'on')
                  ^

elseif strcmp(value, 'off')
                      ^

Change the values to

if strcmp(value, 'On')
                  ^

elseif strcmp(value, 'Off')
                      ^  

or use strcmpi which ignore case.