Write Constructors for Chart Classes

When you develop a chart as a subclass of the ChartContainer base class, the base class provides a default constructor that accepts optional name-value pair arguments for setting chart properties. For example, this command creates an instance of a class called ConfidenceChart.

ConfidenceChart('XData',x,'YData',y,'ConfidenceMargin',0.15,'Color',[1 0 0])

By writing a custom constructor method, you can provide an interface that accepts individual argument values and optional name-value pair arguments. For example, you can design a custom constructor to change the calling syntax for ConfidenceChart so that both of these commands are valid ways to create the chart:

ConfidenceChart(x,y,0.15)
ConfidenceChart(x,y,0.15,'Color',[1 0 0])

When you write the constructor method:

• Specify the input arguments you want to support in the function declaration. Include varargin as the last input argument to capture any property name-value pair arguments that the user specifies.

• Call the ChartContainer constructor before all other references to the chart object.

For example, the following constructor method for the ConfidenceChart class performs these tasks:

• Checks the number of input arguments and returns an error if the number is less than three.

• Converts the x, y, and margin values to the name-value pair arguments that the ChartContainer constructor accepts, and stores the results in args.

• Appends any user-specified name-value pair arguments to the end of args.

• Passes args to the ChartContainer constructor method.

methods
    function obj = ConfidenceChart(x,y,margin,varargin)
        % Check for at least three inputs
        if nargin < 3
            error('Not enough inputs');
        end
            
        % Convert x, y, and margin into name-value pairs
        args = {'XData', x, 'YData', y, 'ConfidenceMargin', margin};
            
        % Combine args with user-provided name-value pairs
        args = [args varargin];
            
        % Call superclass constructor method
        [e-mail](args{:});
    end
end

Example: Confidence Bounds Chart with Custom Constructor

This example shows how to develop a chart that has a custom constructor that accepts single-value input arguments and optional name-value pair arguments. The chart plots a line with markers and a surrounding confidence margin.

Create a program file named ConfidenceChart.m in a folder that is on the MATLAB^® path. Define the class by following these steps.

Step	Implementation
Derive from the ChartContainer base class.	classdef ConfidenceChart < matlab.graphics.chartcontainer.ChartContainer
Define public properties.	properties XData (1,:) double = NaN YData (1,:) double = NaN ConfidenceMargin (1,1) double = 0.15 MarkerSymbol (1,:) char = 'o' Color (1,3) double {mustBeGreaterThanOrEqual(Color,0),... mustBeLessThanOrEqual(Color,1)} = [1 0 0] end
Define private properties.	properties(Access = private,Transient,NonCopyable) LineObject (1,1) matlab.graphics.chart.primitive.Line PatchObject (1,1) matlab.graphics.primitive.Patch end
Implement the custom constructor method that accepts the x, y, and margin values and optional property name-value pair arguments.	methods function obj = ConfidenceChart(x,y,margin,varargin) % Check for at least three inputs if nargin < 3 error('Not enough inputs'); end % Convert x, y, and margin into name-value pairs args = {'XData', x, 'YData', y, 'ConfidenceMargin', margin}; % Combine args with user-provided name-value pairs. args = [args varargin]; % Call superclass constructor method [e-mail](args{:}); end end
Implement the setup method.	methods(Access = protected) function setup(obj) % get the axes ax = getAxes(obj); % Create Patch and objects obj.PatchObject = patch(ax,NaN,NaN,'r','FaceAlpha',0.2,... 'EdgeColor','none'); hold(ax,'on') obj.LineObject = plot(ax,NaN,NaN); hold(ax,'off') end
Implement the update method.	function update(obj) % Update XData and YData of Line obj.LineObject.XData = obj.XData; obj.LineObject.YData = obj.YData; % Update patch XData and YData x = obj.XData; obj.PatchObject.XData = [x x(end:-1:1)]; y = obj.YData; c = obj.ConfidenceMargin; obj.PatchObject.YData = [y+c y(end:-1:1)-c]; % Update colors obj.LineObject.Color = obj.Color; obj.PatchObject.FaceColor = obj.Color; % Update markers obj.LineObject.Marker = obj.MarkerSymbol; end end end

Next, create an instance of a ConfidenceChart. Specify the x- and y-coordinates, the margin value, and a marker symbol.

x = 0:0.2:10;
y = besselj(0,x);
ConfidenceChart(x,y,0.20,'MarkerSymbol','>');