Very weird Dot indexing is not supported for variables of this type

I just built my first Matlab class definition, designed to participate in my .mlapp program.

Here's an excerpt of my .mlapp file:

properties (Access = public)
        UIAxes3 % another detail plot
        Detail1
    end
       
    % Callbacks that handle component events
    methods (Access = private)

        % Code that executes after component creation
        function startupFcn(app)
            xlabel(app.UIAxes, '')
            ylabel(app.UIAxes, '')
            xlabel(app.UIAxes2, '')
            ylabel(app.UIAxes2, '')
            app.UIAxes2.XLim = [0 .3];
            x = linspace(-1,1,200);
            y = cos(x * app.FrequencyEditField.Value);
            x
            y
            app.UIAxes3 = uiaxes(app.UIFigure);
            title(app.UIAxes3, 'Extra')
            app.UIAxes3.Position = [462 31 147 129];
            app.UIAxes3.XLim = [.3 .6];
            plot(app.UIAxes,x,y)
            plot(app.UIAxes2,x,y)
            plot(app.UIAxes3,x,y)
            app.Detail1 = DetailGroup(app, 300, 500)
        end

	. . .
    end

Here's the error it gave me.

    Error using DetailGroup
    Dot indexing is not supported for variables of this type.
    Error in TryApp/startupFcn (line 52)
    app.Detail1 = DetailGroup(app, 300, 500)   

Makes no sense! In the line above, "plot(app.UIAxes3,x,y)", it is perfectly clear that app is the sort of thing that works with dot indexing notation. (all was working until I added the troublesome line.) Is this some misdirected message really meaning to tell me that "DetailGroup is undefined"?

Here's DetailGroup.m, and it's in the same directory with the main mlapp file.

    classdef DetailGroup
        properties
            app
            x
            y
            Graph
            Peak1Label
            Peak1
            Width1Label
            Width1
            Peak2Label
            Peak2
            Width2Label
            Width2
            TOFLabel
            TOF
        end
        
        methods
            function obj = DetailGroup(this, app, x, y)
                % Create Graph
                app.Graph = uiaxes(app.UIFigure);
                title(app.Graph, 'Detail')
                zlabel(app.Graph, 'Z')
                app.Graph.Position = [x y 147 144];
                %            app.Graph.Position = [396 222 147 144];
                
                % Create Peak1Label
                this.Peak1Label = uilabel(this.UIFigure);
                this.Peak1Label.HorizontalAlignment = 'right';
                this.Peak1Label.Position = [x+168 y+111 42 19];
                this.Peak1Label.Text = 'Peak 1';
                
                % Create Peak1
                this.Peak1 = ui(this.UIFigure, 'numeric');
                this.Peak1.Position = [x+225 y+109 54 23];
                
                % Create Width1Label
                this.Width1Label = uilabel(this.UIFigure);
                this.Width1Label.HorizontalAlignment = 'right';
                this.Width1Label.Position = [x+168 y+160 46 22];
                this.Width1Label.Text = 'Width 1';
                
                % Create Width1
                this.Width1 = ui(this.UIFigure, 'numeric');
                this.Width1.Position = [x+225 y+197 54 23];
                
                % Create Peak2Label
                this.Peak2Label = uilabel(this.UIFigure);
                this.Peak2Label.HorizontalAlignment = 'right';
                this.Peak2Label.Position = [x + 168 y+173 42 22];
                this.Peak2Label.Text = 'Peak 2';
                
                % Create Peak2
                this.Peak2 = ui(this.UIFigure, 'numeric');
                this.Peak2.Position = [x+225 y+174 54 23];
                
                % Create Width2Label
                this.Width2Label = uilabel(this.UIFigure);
                this.Width2Label.HorizontalAlignment = 'right';
                this.Width2Label.Position = [x+168 y+150 46 22];
                this.Width2Label.Text = 'Width 2';
                
                % Create Width2
                this.Width2 = ui(this.UIFigure, 'numeric');
                this.Width2.Position = [x+225 y+151 54 23];
                
                % Create TOFLabel
                this.TOFLabel = uilabel(this.UIFigure);
                this.TOFLabel.HorizontalAlignment = 'right';
                this.TOFLabel.Position = [x+182 y+127 28 22];
                this.TOFLabel.Text = 'TOF';
                
                % Create TOF
                this.TOF = ui(this.UIFigure, 'numeric');
                this.TOF.Position = [x+225 y+128 54 23];
            end
        end
    end

Answer 1

[Matt J]

You have only passed 3 arguments to DetailGroup when it expects 4. Therefore, it is trying to do operations in which the double value 300 is used to perform dot indexing. Likely, the function signature for DetailGroup should be,

function DetailGroup(this, x, y)

[Ken]

Thanks. I misunderstood constructor syntax. Got it.

Except: I would have expected the error to originate within the DetailGroup constructor, not in the call to it. Right??

[Matt J]

Thanks. I misunderstood constructor syntax. Got it.

You're welcome. Please Accept-click the answer to indicate that your question is resolved.

Except: I would have expected the error to originate within the DetailGroup constructor, not in the call to it. Right??

Both would appear in the error message normally.