Chart Development Overview - MATLAB & Simulink (original) (raw)

Charting functions such as plot, scatter, and bar enable you to quickly visualize your data with basic control over aspects such as color and line style. To create custom charts, you can combine multiple graphics objects, set properties on those objects, or call additional functions. A common way to store your customization code and share it with others is to write a script or a function. However, other people might have to be to be familiar with your code if they want to use it and make customizations of their own.

As an alternative, you can create a class implementation for your charts by defining a subclass of the ChartContainer base class. Creating a class enables you to:

• Provide a convenient interface for your users — When users want to customize an aspect of your chart, they can set a property rather than having to modify and rerun your graphics code. Users can modify properties at the command line or inspect them in the Property Inspector.
• Encapsulate algorithms and primitive graphics objects — You implement methods that perform calculations and manage the underlying graphics objects. Organizing your code in this way allows you to hide implementation details from your users.

When you define a chart that derives from this base class, instances of your chart are members of the graphics object hierarchy. As a result, your charts are compatible with many aspects of the graphics system. For example, the gca and findobj functions can return instances of your chart.

Structure of a Chart Class

The first line of a chart class specifies the matlab.graphics.chartcontainer.ChartContainer class as the superclass. For example, the first line of a class called ConfidenceChart looks like this:

classdef ConfidenceChart < matlab.graphics.chartcontainer.ChartContainer

In addition to specifying the superclass, include the following components in your class definition.

Implicit Constructor Method

You do not have to write a constructor method for your class because a constructor is inherited from the ChartContainer base class. The constructor accepts optional input arguments: a parent container and any number of name-value pair arguments for setting properties on the chart. For example, if you define a class called ConfidenceChart that has the public propertiesXData and YData, you can create an instance of your class using either of these commands:

c = ConfidenceChart(gcf,'XData',[1 2 3],'YData',[4 5 6]) c = ConfidenceChart('XData',[1 2 3],'YData',[4 5 6])

If you want to provide an interface that accepts input arguments in the same way as a typical function does, you can define a custom constructor method. See Write Constructors for Chart Classes for more information.

Public and Private Property Blocks

Divide your class properties between at least two blocks:

• A public block for storing the components of the user-facing interface
• A private block for storing the implementation details that you want to hide

The properties that go in the public block store the input values provided by the user. For example, a chart that displays a line might store the_x_- and _y_-coordinate vectors in two public properties. Since the property name-value pair arguments are optional inputs to the implicit constructor method, the recommended approach is to initialize the public properties to default values. If you define public properties that store coordinate values, initializing them to NaN values or empty arrays constructs an empty chart if the user calls the constructor without any inputs.

The properties that go in the private block store the underlying graphics objects that make up your chart, in addition to any calculated values you want to store. Eventually, your class will use the data in the public properties to configure the underlying objects. By including the Transient andNonCopyable attributes for the private block, you avoid storing redundant information if the user copies or saves an instance of the chart.

For example, here are the property blocks for a chart that displays aLine object and a Patch object. The public property block stores values that the user can control: the _x_- and _y_-coordinates of the line, a confidence margin value, a marker symbol, and a color value. The private property block stores theLine and Patch objects.

properties XData = NaN YData = NaN ConfidenceMargin = 0.15 MarkerSymbol = 'o' Color = [1 0 0]
end

properties(Access = private,Transient,NonCopyable) LineObject PatchObject end

Setup Method

The setup method executes once when MATLAB constructs the chart object. Any property values passed as name-value pair arguments to the constructor method are assigned after this method executes.

Use the setup method to:

• Call plotting functions to create the primitive graphics objects you want to use in the chart.
• Store the primitive objects returned by the plotting functions as private properties on the chart object.
• Configure the primitive graphics objects.
• Configure the axes.

Many graphics functions have an optional input argument for specifying the target axes object. These functions include plotting functions (such asplot, scatter, andbar) and functions that modify the axes (such ashold, grid, andtitle). When you call these types of functions from within a class method, you must specify the target axes object. You can access the axes object by calling the getAxes method. This method returns the axes object, or it creates a Cartesian axes object if the chart does not already contain an axes object.

Caution

Calling plotting functions, or functions that modify the axes, without specifying the target axes might produce unexpected results.

When you call plotting functions in the setup method, specify temporary values (such as NaN) for the coordinate data. Also, specify temporary values for other arguments that correspond to public properties of your class. Doing so avoids setting the same property values in both thesetup and the update methods.

If you want to display multiple primitive objects in the axes, call thehold function between plotting commands. Set the hold state back to 'off' after your last plotting command.

For example, consider a chart that displays a line and a patch. It has these properties:

• Two public properties called XData andYData for storing the _x_- and_y_-coordinates of the line
• Two private properties called LineObject andPatchObject

The setup method gets the axes object by calling thegetAxes method. Then it calls the patch function and stores the output in the PatchObject property. The next line of code set the hold state of the axes to 'on' before calling the plot function to create theLineObject property. The last line of code sets the axes hold state back to 'off'.

function setup(obj) % Get the axes ax = getAxes(obj);

% Create Patch and Line objects
obj.PatchObject = patch(ax,NaN,NaN,'r','FaceAlpha',0.2,...
    'EdgeColor','none');
hold(ax,'on')
obj.LineObject = plot(ax,NaN,NaN);
        
% Turn hold state off
hold(ax,'off')

end

Update Method

When the user changes one or more property values on the chart object, MATLAB marks the chart object for updating. The update method runs for the first time after the setup method runs. Then it runs the next time drawnow executes. Thedrawnow function automatically executes periodically, based on the state of the graphics environment in the user's MATLAB session. Thus, there might be a delay between changing property values and seeing the results of those changes.

Use the update method to reconfigure the underlying graphics objects in your chart based on the new values of the properties. Typically, this method does not distinguish which of the properties changed. It reconfigures all aspects of the underlying graphics objects that depend on the properties.

For example, consider a chart that has these properties:

• Two public properties called XData andColor
• Two private properties called LineObject andPatchObject

The update method updates theXData and Color properties of theLine and Patch objects.

function update(obj)

% Update XData of line object
obj.LineObject.XData = obj.XData;
        
% Update patch XData 
x = obj.XData;
obj.PatchObject.XData = [x x(end:-1:1)];
        
% Update line object colors
obj.LineObject.Color = obj.Color;
obj.PatchObject.FaceColor = obj.Color;
       

end

Example: Confidence Bounds Chart

This example shows how to create a chart for plotting a line with confidence bounds. Create a class definition file named ConfidenceChart.m in a folder that is on the MATLAB path. Define the class by following these steps.

Next, create an instance of the chart by calling the implicit constructor method with a few of the public properties:

x = 0:0.2:10; y = besselj(0,x); c = ConfidenceChart('XData',x,'YData',y,'ConfidenceMargin',0.15);

Change the color.

Tip

In addition to the examples provided in the documentation, you can find a variety of community authored examples on File Exchange at MATLAB Central™.

Support Common Graphics Features

By default, instances of your charts support much of the functionality that is common to all MATLAB charts. For example, the gca andfindobj functions can return instances of your chart. You can also pass instances of your chart to the set andget functions, and you can configure the properties of the chart in the Property Inspector.

The features described in this table are supported only if you enable them for your chart.

See Also

Classes

• matlab.graphics.chartcontainer.ChartContainer

Functions

• plot | patch

Properties

• Line Properties | Patch Properties

Topics

• Define Classes
• Develop Charts With Polar Axes, Geographic Axes, or Multiple Axes