MATLAB: Changing Value with Slider in App Designer

appdesignerchange value with sliderguislider

1

Best Answer

Ah, I misread your first post. But your second post clarifies everything. You have two problems:
On your line 103, your callback function to the slider value change is named GenerateButtonPushed. But in line 60, you call it as RPMSliderValueChanging - and this function does not exist, so you will not get any new n values read.
In addition, in your actual GenerateButtonPushed function, line 24, you set n=140 every time you push the generate button, so even if the slider read a new n, when you push the button you set n=140 again. Define n outside of your function - for example, on line 105, where you define all the GUI options is a good place to "initialize values".
This also means my first suggestion can be deleted - I have done this, and introduced the two other things, it seems to work for me although your axes are a little restrictive :) 
classdef app1 < matlab.apps.AppBase
    % Properties that correspond to app components
    properties (Access = public)
        UIFigure        matlab.ui.Figure
        GenerateButton  matlab.ui.control.Button
        RPMSliderLabel  matlab.ui.control.Label
        RPMSlider       matlab.ui.control.Slider
    end
    
    
    methods (Access = private)
        % Callback function: GenerateButton, RPMSlider
        function GenerateButtonPushed(app, event)
global a         
global V_f       
global L           
global S         
global n       
global D          
a = 10;
V_f = 15;
L = 50;
S =120;   
%n =140;      If you have the n here, it is hardset to 140 every time you push the button
D=50;  
x = 1:50; 
y = 1:50;   
V_w = (V_f * pi * D * n)/(2*L*S);
for i = 1:length(y)
    hor(i) = V_w * sqrt(2*y(i)/a);
    i = i+1;
end
plot(y,hor, 'r')
hold on
for i=1:100
    k = y - i;
    plot(k, hor, 'r')
    hold on
     m = -x - i;
    plot(m, hor, 'b')
    hold on
    i= i +1;
end
hold off
if L<75
axis([-35 -10 20 34])
elseif L<200
    axis([-35 -10 8 20])
elseif L<350
   axis([-35 -10 3.5 6])
elseif L>800
         axis([-35 -15 1.5 2.5])     
else 
    axis([-35 -10 2 4])
end
set(gca,'xtick',[])
set(gca,'ytick',[])
        end
        % Callback function
        function RPMSliderValueChanging(~, event)
            global n 
           changingValue = event ; 
n = changingValue.Value ;
        end
    end
    % App initialization and construction
    methods (Access = private)
        % Create UIFigure and components
        function createComponents(app)
            % Create UIFigure
            app.UIFigure = uifigure;
            app.UIFigure.Position = [100 100 368 359];
            app.UIFigure.Name = 'UI Figure';
            % Create GenerateButton
            app.GenerateButton = uibutton(app.UIFigure, 'push');
            app.GenerateButton.ButtonPushedFcn = createCallbackFcn(app, @GenerateButtonPushed, true);
            app.GenerateButton.Position = [119 89 100 22];
            app.GenerateButton.Text = 'Generate';
            % Create RPMSliderLabel
            app.RPMSliderLabel = uilabel(app.UIFigure);
            app.RPMSliderLabel.HorizontalAlignment = 'right';
            app.RPMSliderLabel.Position = [61 223 32 22];
            app.RPMSliderLabel.Text = 'RPM';
            % Create RPMSlider
            app.RPMSlider = uislider(app.UIFigure);
            app.RPMSlider.Limits = [0 250];
            app.RPMSlider.ValueChangingFcn = createCallbackFcn(app, @RPMSliderValueChanging, true);   %The function must be named rightly :) 
            app.RPMSlider.Position = [104 232 160 3];
            app.RPMSlider.Value = 140;
            global n
            n=140;     %Define your n outside of the button push function
        end
    end
    methods (Access = public)
        % Construct app
        function app = app1
            % Create and configure components
            createComponents(app)
            % Register the app with App Designer
            registerApp(app, app.UIFigure)
            if nargout == 0
                clear app
            end
        end
        % Code that executes before app deletion
        function delete(app)
            % Delete UIFigure when app is deleted
            delete(app.UIFigure)
        end
    end
end
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