Read/write text file in an app

I have something quite simple that seems somehow very difficult to do! I would like to print a text file, then later read it, from an app. The text is just ascii text, not data, tables, numbers or arrays or anything like that. The text comes from and will be sent back to app.textarea.value. I want to make notes in this text area, save them, then recall them. The notes may have paragraphs and so on. I just want to save it as text, and read it back in as text. What is the simplest way to do this?

[Miguel Angel]

I've just write this code, hope it helps you. The value that the textarea returns is always a cell, so I put it in a for and parse it into a string and then use the function fprintf to write everything in a .txt file. The only problem is that, apparentely this function cannot add newlines to my .txt file, so I was thinking about print some special characters and then use some code to retrieve the text and add the newlines by coding.

Here I show you the code view of my matlab app.

classdef libreta < matlab.apps.AppBase

    % Properties that correspond to app components
    properties (Access = public)
        UIFigure               matlab.ui.Figure
        CargarnotaButton       matlab.ui.control.Button
        GuardarnotaButton      matlab.ui.control.Button
        MisnotasTextArea       matlab.ui.control.TextArea
        MisnotasTextAreaLabel  matlab.ui.control.Label
    end

    
    properties (Access = private)
        nombreArchivo = "miNota.txt"; % Description
    end
    
    methods (Access = private)
        function guardaTexto(app)
        %% escribiendo/creando archivo json
            fid = fopen(app.nombreArchivo,"w");% w es de write, escritura
            for i = 1:1:length(app.MisnotasTextArea.Value)
                fprintf(fid,'%s',string(app.MisnotasTextArea.Value(i)));
            end
            fclose(fid);
        end

        function cargaTexto(app)
            fid = fopen(app.nombreArchivo,"r"); % r es de read, lectura
            app.MisnotasTextArea.Value = fscanf(fid,'%c');
            fclose(fid);
        end
    end
    

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

        % Button pushed function: GuardarnotaButton
        function GuardarnotaButtonPushed(app, event)
            guardaTexto(app);
        end

        % Button pushed function: CargarnotaButton
        function CargarnotaButtonPushed(app, event)
            cargaTexto(app);
        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 = [100 100 640 480];
            app.UIFigure.Name = 'MATLAB App';

            % Create MisnotasTextAreaLabel
            app.MisnotasTextAreaLabel = uilabel(app.UIFigure);
            app.MisnotasTextAreaLabel.HorizontalAlignment = 'right';
            app.MisnotasTextAreaLabel.Position = [208 413 56 22];
            app.MisnotasTextAreaLabel.Text = 'Mis notas';

            % Create MisnotasTextArea
            app.MisnotasTextArea = uitextarea(app.UIFigure);
            app.MisnotasTextArea.Position = [274 147 327 288];

            % Create GuardarnotaButton
            app.GuardarnotaButton = uibutton(app.UIFigure, 'push');
            app.GuardarnotaButton.ButtonPushedFcn = createCallbackFcn(app, @GuardarnotaButtonPushed, true);
            app.GuardarnotaButton.Position = [41 403 100 22];
            app.GuardarnotaButton.Text = 'Guardar nota';

            % Create CargarnotaButton
            app.CargarnotaButton = uibutton(app.UIFigure, 'push');
            app.CargarnotaButton.ButtonPushedFcn = createCallbackFcn(app, @CargarnotaButtonPushed, true);
            app.CargarnotaButton.Position = [41 341 100 22];
            app.CargarnotaButton.Text = 'Cargar nota';

            % 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 = libreta

            % 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

Answer 1

[Jiahao CHANG]

Hi Peter,

I think you can use the function fopen and fprintf to create and write to text file.

Then, you can try to use fgets or fgetl to read line from file.

Use some loop so that you can read full line for your text file.

[Peter de Goot]

Yes well, I have been trying for a couple of hours. It seems not a natural thing to do. The text area is stored as a character string, or as a vector of character strings. A new line in the text area creates a new line characters in a second row of the vector. If you just read/write character by character, the paragraphs are lost. So it is is not so straightforward, I have not found any examples of how to do this.