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.

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:

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 

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

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

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:

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:

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:

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.

classdef ColorSelector < matlab.ui.componentcontainer.ComponentContainer

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

    events (HasCallbackProperty, NotifyAccess = protected) 
        ValueChanged % ValueChangedFcn will be the generated callback property 
    end

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

    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

        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

    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.