Function in App-Designer struggles to read dropdown values

Hi,

i want to build a very simple app with code that works fine in the regular matlab-editor. In App-Designer i tried to implement just a start-button to run the code and 2 dropdown-lists to select input for the main function.

When i run the programm it seems like the main-function works, but has struggle to read the values from the dropdown lists. See the example below:

% Callbacks that handle component events
    methods (Access = private)

        % Button pushed function: StartButton (This is the code i wrote in
        % the regular editor.)
        function StartButtonPushed(app, event)
            % Sample rate
            fs = 48000
            adr = audioDeviceReader(fs);
            buff = dsp.AsyncBuffer(Capacity = fs*3);

            numIterations = floor(450*fs/adr.SamplesPerFrame);

            o=1;
            
            for index=1:numIterations

                frame = adr();

                write(buff,frame);

                if buff.NumUnreadSamples >= 2*fs
                    o=o+1;
                    data = read(buff);

                    [psp, f] = pspectrum(data,fs);
            
                    f_index = find(f >= app.minFrequencyDropDown.Value & f <= app.maxFrequencyDropDown.Value);
                    
                    p = 10*log10(psp(f_index));
                    m(o,:)   = mean(p) %m is the value im interested in!

                end
            end
        end

        
         % Value changed function: minFrequenzDropDown
         function minFrequencyDropDownValueChanged(app, event)
            value = app.minFrequencyDropDown.Value;
        end

        % Value changed function: maxFrequenzDropDown
        function maxFrequencyDropDownValueChanged(app, event)
            value = app.maxFrequencyDropDown.Value;
        end
        

i tried setting properties like "minFrequency" and "maxFrequency" and i tried different syntax in the dropdown functions, but somehow i keep getting NaN Values in m(o,:)

Really appreciate any help! Thanks.

Answer 1

[Simon Chan]

Use function str2double as follows:

% Value changed function: minFrequenzDropDown
         function minFrequencyDropDownValueChanged(app, event)
            value = str2double(app.minFrequencyDropDown.Value); 
        end
        % Value changed function: maxFrequenzDropDown
        function maxFrequencyDropDownValueChanged(app, event)
            value = str2double(app.maxFrequencyDropDown.Value);
        end