Develop Custom UI Components Programmatically

To create custom UIs and visualizations, you can combine multiple graphics and UI objects, change their properties, or call additional functions. In R2020a and earlier releases, a common way to store your customization code and share it with others is to write a script or a function.

Starting in R2020b, instead of a script or function, you can create a class implementation for your UI components by defining a subclass of the ComponentContainer base class. Creating a class has these benefits:

• Easy customization — When users want to customize an aspect of your UI component, they can set a property rather than having to modify and rerun your code. Users can modify properties at the command line or inspect them in the Property Inspector.

• Encapsulation — Organizing your code in this way allows you to hide implementation details from your users. You implement methods that perform calculations and manage the underlying graphics objects.

This topic gives an overview of the steps to create a custom UI component by defining a class programmatically. Alternatively, starting in R2022a, you can create a custom UI component interactively using App Designer. For more information about the interactive approach, see Create a Simple Custom UI Component in App Designer.

Structure of a UI Component Class

A UI component class has several required parts, and several more that are optional.

In the first line of a UI component class, specify the matlab.ui.componentcontainer.ComponentContainer class as the superclass. For example, the first line of a class called ColorSelector looks like this:

classdef ColorSelector < matlab.ui.componentcontainer.ComponentContainer

In addition to specifying the superclass, include the following components in your class definition. Some components are required, while other components are either recommended or optional.

Component	Description
Public property block (recommended)	This block defines all the properties that users have access to. Together, these properties make up the user interface of your UI component.
Private property block (recommended)	This block defines the underlying graphics objects and other implementation details that users cannot access. In this block, set these attribute values: Access = private Transient NonCopyable
Events block (optional)	This block defines the events that this UI component will trigger. In this block, set these attribute values: HasCallbackProperty NotifyAccess = protected When you set the HasCallbackProperty attribute, MATLAB® creates a public property for each event in the block. The public property stores the user-provided callback to execute when the event fires.
setup method (required)	This method sets the initial state of the UI component. It executes once when MATLAB constructs the object. Define this method in a protected methods block.
update method (required)	This method updates the underlying objects in your UI component. It executes under the following conditions: During the next drawnow execution after the user changes one or more property values When an aspect of the user's graphics environment changes (such as the size) Define this method in the same protected block as the setup method.

Constructor Method

You do not have to write a constructor method for your class, because it inherits one from the ComponentContainer base class. The inherited constructor accepts optional input arguments: a parent container and any number of name-value pair arguments for setting properties on the UI component. For example, if you define a class called ColorSelector that has the public properties Value and ValueChangedFcn, you can create an instance of your class using this code:

f = uifigure; 
c = ColorSelector(f,'Value',[1 1 0],'ValueChangedFcn',@(o,e)disp('Changed'))

If you want to provide a constructor that has a different syntax or different behavior, you can define a custom constructor method. For an example of a custom constructor, see Write Constructors for Chart Classes.

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 UI component that allows a user to pick a color value might store the color value in a public property. 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.

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

For example, here are the property blocks for a UI component that allows a user to pick a color value. The public property block stores the value that the user can control: the color value. The private property block stores the grid layout manager, button, and edit field objects.

properties
    Value {validateattributes(Value, ...
        {'double'},{'<=',1,'>=',0,'size',[1 3]})} = [1 0 0];   
end

properties (Access = private,Transient,NonCopyable)
    Grid matlab.ui.container.GridLayout 
    Button matlab.ui.control.Button 
    EditField matlab.ui.control.EditField
end   

Event Block

You optionally can add a third block for events that the UI component fires.

Create a public property for each event in the block by specifying the HasCallbackProperty attribute. The public property stores the user-provided callback to execute when the event fires. The name of the public property is the name of the event appended with the letters Fcn. For example, a UI component that allows a user to pick a color value might define the event ValueChanged, which generates the corresponding public property ValueChangedFcn. Use the notify method to fire the event and execute the callback in the property.

For example, here is the event block for a UI component that allows a user to pick a color value.

events (HasCallbackProperty, NotifyAccess = protected) 
    ValueChanged 
end 

When the user picks a color value, call the notify method to fire the ValueChanged event and execute the callback in the ValueChangedFcn property.

function getColorFromUser(comp)
    c = uisetcolor(comp.Value);
    if (isscalar(c) && (c == 0))
        return;
    end
    
    % Update the Value property
    oldValue = comp.Value;
    comp.Value = c;

    % Execute user callbacks and listeners
    notify(comp,'ValueChanged');
end

When a user creates an instance of the UI component, they can specify a callback to execute when the color value changes using the generated public property.

f = uifigure; 
c = ColorSelector(f,'ValueChangedFcn',@(o,e)disp('Changed'))

For more information about specifying callbacks to properties, see Create Callbacks for Apps Created Programmatically.

Setup Method

Define a setup method for your class. A setup method executes once when MATLAB constructs the UI component object. Any property values passed as name-value arguments to the constructor method are assigned after this method executes.

Use the setup method to:

• Create graphics and UI objects that make up the component.

• Store the objects as private properties on the component object.

• Lay out and configure the objects.

• Wire up the objects to do something useful within the component.

Define the setup method in a protected block.

Most UI object creation functions have an optional input argument for specifying the parent. When you call these functions from within a class method, you must specify the target parent. Specify the target parent as the UI component object being set up by using the class instance argument passed to the method.

For example, consider a UI component that has these properties:

• One public property called Value

• Three private properties called Grid, Button, and EditField

The setup method calls the uigridlayout, uieditfield, and uibutton functions to create the underlying graphics object for each private property, specifying the instance of the UI component (comp) as the target parent.

function setup(comp) 
    % Create grid layout to manage building blocks 
    comp.Grid = uigridlayout(comp,[1 2],'ColumnWidth',{'1x',22},... 
        'RowHeight',{'fit'},'ColumnSpacing',2,'Padding',2); 

    % Create edit field for entering color value
    comp.EditField = uieditfield(comp.Grid,'Editable',false,... 
        'HorizontalAlignment','center'); 

    % Create button to confirm color change
    comp.Button = uibutton(comp.Grid,'Text',char(9998), ... 
        'ButtonPushedFcn',@(o,e) comp.getColorFromUser()); 
end 

Update Method

Define an update method for your class. This method executes when your UI component object needs to change its appearance in response to a change in values.

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

For example, consider a UI component that has these properties:

• One public property called Value

• Three private properties called Grid, Button, and EditField

The update method updates the BackgroundColor of the EditField and Button objects with the color stored in Value. The update method also updates the EditField object with a numeric representation of the color. This way, however Value is changed, the change becomes equally visible everywhere.

function update(comp)      
    % Update edit field and button colors 
    set([comp.EditField comp.Button],'BackgroundColor',comp.Value, ... 
        'FontColor',comp.getContrastingColor(comp.Value));  

    % Update edit field display text 
    comp.EditField.Value = num2str(comp.Value,'%0.2g ');            

end

There might be a delay between changing property values and seeing the results of those changes. The update method runs for the first time after the setup method runs and then it runs every time drawnow executes. The drawnow function automatically executes periodically, based on the state of the graphics environment in the user's MATLAB session. This periodic execution can lead to the potential delay.

Example: Color Selector UI Component

This example shows how to create a UI component for selecting a color, using the code discussed in other sections of this page. Create a class definition file named ColorSelectorComponent.m in a folder that is on the MATLAB path. Define the class by following these steps.

Step	Implementation
Derive from the ComponentContainer base class.	classdef ColorSelector < matlab.ui.componentcontainer.ComponentContainer
Define public properties.	properties Value {validateattributes(Value, ... {'double'},{'<=',1,'>=',0,'size',[1 3]})} = [1 0 0]; end
Define public events.	events (HasCallbackProperty, NotifyAccess = protected) ValueChanged % ValueChangedFcn will be the generated callback property end
Define private properties.	properties (Access = private, Transient, NonCopyable) Grid matlab.ui.container.GridLayout Button matlab.ui.control.Button EditField matlab.ui.control.EditField end
Implement the setup method. In this case, call the uigridlayout, uieditfield, and uibutton functions to create GridLayout, EditField, and Button objects. Store those objects in the corresponding private properties. Specify the getColorFromUser method as the ButtonPushedFcn callback that is called when the button is pressed.	methods (Access = protected) function setup(comp) % Grid layout to manage building blocks comp.Grid = uigridlayout(comp,[1,2],'ColumnWidth',{'1x',22}, ... 'RowHeight',{'fit'},'ColumnSpacing',2,'Padding',2); % Edit field for value display and button to launch uisetcolor comp.EditField = uieditfield(comp.Grid,'Editable',false, ... 'HorizontalAlignment','center'); comp.Button = uibutton(comp.Grid,'Text',char(9998), ... 'ButtonPushedFcn',@(o,e) comp.getColorFromUser()); end
Implement the update method. In this case, update the background color of the underlying objects and the text in the edit field to show the color value.	function update(comp) % Update edit field and button colors set([comp.EditField comp.Button],'BackgroundColor',comp.Value, ... 'FontColor',comp.getContrastingColor(comp.Value)); % Update the display text comp.EditField.Value = num2str(comp.Value,'%0.2g '); end end
Wire the callbacks and other pieces together using private methods. When the getColorFromUser method is triggered by a button press, call the uisetcolor function to open the color picker and then call the notify function to execute the user callback and listener functions. When the getContrastingColor method is called by the update method, calculate whether black or white text is more readable on the new background color.	methods (Access = private) function getColorFromUser(comp) c = uisetcolor(comp.Value); if (isscalar(c) && (c == 0)) return; end % Update the Value property comp.Value = c; % Execute user callbacks and listeners notify(comp,'ValueChanged'); end function contrastColor = getContrastingColor(~,color) % Calculate opposite color c = color * 255; contrastColor = [1 1 1]; if (c(1)*.299 + c(2)*.587 + c(3)*.114) > 186 contrastColor = [0 0 0]; end end end end

Next, create an instance of the UI component by calling the implicit constructor method with a few of the public properties. Specify a callback to display the words Color changed when the color value changes.

h = ColorSelector('Value', [1 1 0]); 
h.ValueChangedFcn = @(o,e) disp('Color changed');

Click the button and select a color using the color picker. The component changes appearance and MATLAB displays the words Color changed in the Command Window.