Changing Value with Slider in App Designer

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;
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
end

Hi all, I have implemented this code into app designer, and I want to change the 'n' value with slider.

function RPMSliderValueChanging(app, event)
            changingValue = event;
            n = changingValue;
        end

I have created a callback for adjusting the n value. I want to change the n value and then plot the updated figure. However, the plot does not change when I change the value with slider. Can someone please help me. Thanks

[Rena Berman]

(Answers Dev) Restored edit

Answer 1

[Jakob B. Nielsen]

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

[Erkin Karatas]

thanks a lot

Answer 2

[Inso]

This is because 'n' is not a global variable in RPMSliderValueChanging function.

You can either claim n to be global in the callback function or create n as a property of you app to pass the data.

[Erkin Karatas]

function RPMSliderValueChanging(app, event)
            global n 
            changingValue = event.Value;
            n = changingValue;
        end

I have claimed it as shown above, but the plotted figure did not change.

[Inso]

call the GenerateButtonPushed function in the RPMSliderValueChanging function after 'n = changingValue;'. And you might need to clear the axes for replot.

[Erkin Karatas]

Stil, no change :(

[Inso]

Sorry I mistype something. It should be:

function RPMSliderValueChanging(app, event)
            global n 
            changingValue = event;
            n = changingValue;
             cla(gca)
            GenerateButtonPushed(app, event)
        end

Also assign all the global variables in the Startup function instead of in GenerateButtonPushed.

Answer 3

[Jakob B. Nielsen]

Currently, all your slider event function does is read a new value of n. The figure will only change if you specifcy that it must, so include that in your slider value change event, and see if that works.

function RPMSliderValueChanging(app, event)
            changingValue = event;
            n = changingValue;
            
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
            
end

[Erkin Karatas]

Unfortunately, I still get the same plot, I am posting the whole code, so that you can see if anything is wrong

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;
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(app, event)
            global n 
           changingValue = event ; 
n = changingValue ; 

            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
        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, @GenerateButtonPushed, true);
            app.RPMSlider.Position = [104 232 160 3];
            app.RPMSlider.Value = 140;
        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