[SOLVED] Taking multiple inputs from user in one box in MATLAB

I think it should have worked...

Make sure to use MATLAB App Designer (you can start it by entering appdesigner in command window).
Make sure to name the edit box firstVal in MATLAB App Designer:

Setting the value to Inf is an improvised solution, but it's important, because waitfor waits for the value to get changed.
Setting the value to Inf after entering a new value forces the user to change the value.
I replaced matrix = xlsread("Transfusion.xlsx"); with matrix = [0, 0, 0, 0, 0, 0];.
Remark: Don't expect us to guess what is the content of "Transfusion.xlsx".
The file is not relevant to the post, because you are only using the size.
Remark: don't be shy, and post the entire App Designer code as a reference (when using a tool like App Designer the tool may hide some important information in the automatically generated code, that may be important for identifying the problem).
Remark: Since it's a follow up post, you should give a reference to your previous post.

Here is a modified version of the function ButtonPushed(app, event):

% Button pushed function: Button
function ButtonPushed(app, event)
    app.Button.Enable = 'Off'; %Disable button while taking input (just nicer).

    %I replaced the xlsread("Transfusion.xlsx") with some arbitrary values, because only the size is relevant
    matrix = [0, 0, 0, 0, 0, 0]; %xlsread("Transfusion.xlsx"); 
    attributesNum = size(matrix,2) - 1;
    X = zeros(attributesNum, 1);

    %Initialize text label with message
    app.ValuesLabel.Text = ['Enter ', num2str(attributesNum), ' values in edit box (set value and press enter)'];

    for i = 1:attributesNum
        waitfor(app.firstVal, 'Value');
        value = app.firstVal.Value;
        X(i, 1) = value;

        %Set to Inf every iteration, because waitfor waits for a change in value (and you may need to enter same value twice).
        app.firstVal.Value = Inf;

        %Update text of ValuesLabel (for demonstrating the concept).
        text = ['Values: ', sprintf('%.1f, ', X(1:i))];
        app.ValuesLabel.Text = text(1:end-2);
    end

    %Display X in Command window for testing
    disp(X)

    app.Button.Enable = 'On'; %Enable button at the end.
end

Here is the complete code (including generated code).
You can copy and paste it to App1.m file just to see how it works.

classdef app1 < matlab.apps.AppBase

    % Properties that correspond to app components
    properties (Access = public)
        UIFigure        matlab.ui.Figure
        EditFieldLabel  matlab.ui.control.Label
        firstVal        matlab.ui.control.NumericEditField
        ValuesLabel     matlab.ui.control.Label
        Button          matlab.ui.control.Button
    end



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

        % Button pushed function: Button
        function ButtonPushed(app, event)
            app.Button.Enable = 'Off'; %Disable button while taking input (just nicer).

            %I replaced the xlsread("Transfusion.xlsx") with some arbitrary values, because only the size is relevant
            matrix = [0, 0, 0, 0, 0, 0]; %xlsread("Transfusion.xlsx"); 
            attributesNum = size(matrix,2) - 1;
            X = zeros(attributesNum, 1);

            %Initialize text label with message
            app.ValuesLabel.Text = ['Enter ', num2str(attributesNum), ' values in edit box (set value and press enter)'];

            for i = 1:attributesNum
                waitfor(app.firstVal, 'Value');
                value = app.firstVal.Value;
                X(i, 1) = value;

                %Set to Inf every iteration, because waitfor waits for a change in value (and you may need to enter same value twice).
                app.firstVal.Value = Inf;

                %Update text of ValuesLabel (for demonstrating the concept).
                text = ['Values: ', sprintf('%.1f, ', X(1:i))];
                app.ValuesLabel.Text = text(1:end-2);
            end

            %Display X in Command window for testing
            disp(X)

            app.Button.Enable = 'On'; %Enable button at the end.
        end
    end

    % Component initialization
    methods (Access = private)

        % Create UIFigure and components
        function createComponents(app)

            % Create UIFigure and hide until all components are created
            app.UIFigure = uifigure('Visible', 'off');
            app.UIFigure.Position = [100 100 369 256];
            app.UIFigure.Name = 'UI Figure';

            % Create EditFieldLabel
            app.EditFieldLabel = uilabel(app.UIFigure);
            app.EditFieldLabel.HorizontalAlignment = 'right';
            app.EditFieldLabel.Position = [45 123 56 22];
            app.EditFieldLabel.Text = 'Edit Field';

            % Create firstVal
            app.firstVal = uieditfield(app.UIFigure, 'numeric');
            app.firstVal.Position = [116 123 100 22];
            app.firstVal.Value = Inf;

            % Create ValuesLabel
            app.ValuesLabel = uilabel(app.UIFigure);
            app.ValuesLabel.Position = [49 51 297 22];
            app.ValuesLabel.Text = 'Values: ';

            % Create Button
            app.Button = uibutton(app.UIFigure, 'push');
            app.Button.ButtonPushedFcn = createCallbackFcn(app, @ButtonPushed, true);
            app.Button.Tooltip = {'Press to start taking input'};
            app.Button.Position = [46 204 120 32];

            % Show the figure after all components are created
            app.UIFigure.Visible = 'on';
        end
    end

    % App creation and deletion
    methods (Access = public)

        % Construct app
        function app = app1

            % Create UIFigure and 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