MATLAB: Calling a function defined in a m-file from within appdesigner app, with the app object as function input

appdesigner

I'm using R2019b.

I have created a GUI app using appdesigner and have written the function testFun in a m-file (testFun should also be usable by a non GUI approach, hence the m-file).

Within the app, I have declared a public property called someData:

properties (Access = public)
    someData = '';
end

From within the GUI app, testFun is called with app as a function argument:

testFun(app)

testFun is defined as follows:

function testFun(inputData)
    inputData.someData = 'hello world';
end

As you can see, there are no output arguments defined in testFun.

Yet when I run the app like this, the someData property gets the value 'hello world'.

How can this behavior be explained?

Best Answer

Your GUI (like all AppDesigner GUIs) has a pass-by-reference behavior (so it behaves like a handle class). That means the line you show modifies the original object, instead of creating a new one when the function is called.

You could create a GUI that doesn't work this way by using the normal figure class, so what is generally meant by a 'programmatic GUI', or GUIs created with GUIDE. For an overview of your options for GUI design, see this. For more information about pass-by-reference vs pass-by-value, see Comparison of handle and value classes in the documentation.

Related Solutions

MATLAB: App Designer How to “StartUp” within the App

(1) Two possibilities to reset your app to its default state:

https://www.mathworks.com/matlabcentral/answers/489003-reset-or-clear-property-values-in-app-designer#comment_763148

https://www.mathworks.com/matlabcentral/answers/489003-reset-or-clear-property-values-in-app-designer#answer_399598

I prefer the first. A simple example using a function called resetComponents:

classdef app1 < matlab.apps.AppBase
    % Properties that correspond to app components
    properties (Access = public)
        UIFigure        matlab.ui.Figure
        EditFieldLabel  matlab.ui.control.Label
        EditField       matlab.ui.control.EditField
        Button          matlab.ui.control.Button
    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 = 'UI Figure';
            % Create EditFieldLabel

            app.EditFieldLabel = uilabel(app.UIFigure);
            app.EditFieldLabel.HorizontalAlignment = 'right';
            app.EditFieldLabel.Position = [382 282 56 22];
            app.EditFieldLabel.Text = 'Edit Field';
            % Create EditField

            app.EditField = uieditfield(app.UIFigure, 'text');
            app.EditField.Position = [453 282 100 22];
            % Create Button

            app.Button = uibutton(app.UIFigure, 'push');
            app.Button.Position = [129 282 100 22];
            app.Button.Text = 'Reset';
            app.Button.ButtonPushedFcn = @app.resetButtonCallback;
            % Show the figure after all components are created
            app.UIFigure.Visible = 'on';
        end
        
        function resetComponents(app)
            % Create EditFieldLabel
            app.EditFieldLabel = uilabel(app.UIFigure);
            app.EditFieldLabel.HorizontalAlignment = 'right';
            app.EditFieldLabel.Position = [382 282 56 22];
            app.EditFieldLabel.Text = 'Edit Field';
            % Create EditField
            app.EditField = uieditfield(app.UIFigure, 'text');
            app.EditField.Position = [453 282 100 22];
            % Create Button
            app.Button = uibutton(app.UIFigure, 'push');
            app.Button.Position = [129 282 100 22];
            app.Button.Text = 'Reset';
            app.Button.ButtonPushedFcn = @app.resetButtonCallback;
            
            % Or, alternatively, instead of redefining each component, just figure out all
            % properties which could be changed by the user and reset them to their
            % defaults:
            %

            % app.EditField.Value = '';
            %
            % Simpler here, but takes more work for more complicated apps.
        end
        
        function resetButtonCallback(app, ~, ~)
            resetComponents(app);
        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

(2) You can access a callback function if you have access to an instance of the app and you are calling from a location allowed by the function's Access attribute (e.g. Public, Private, etc).

Example 1: You cannot call a callback function from within a static method, because the static method does not have access to an instance of the app.

Example 2: You cannot call a callback function externally if its Access attribute is Private.

MATLAB: Reset GUI M-File

Delete the associated .m file and reopen the GUI in GUIDE. In GUIDE, open Tools > GUI options... check "Generate FIG file and MATLAB file" and save the GUI.

Best Answer

Related Solutions

MATLAB: App Designer How to “StartUp” within the App

MATLAB: Reset GUI M-File

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