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Create a Simple Custom UI Component in App Designer

In addition to the UI components that MATLAB^® provides for building apps, you can create custom UI components to use in your own apps or to share with others. Starting in R2022a, you can interactively create custom UI components in App Designer.

Some benefits of creating custom UI components include:

Modularization — Separate the display and code of large apps into independent, maintainable pieces.
Reusability — Provide a convenient interface for adding and customizing similar components in apps.
Flexibility — Extend the appearance and behavior of existing UI components.

Component Creation Overview

When you design and create a custom UI component, there are two users of your component to consider: app creators and app users. App creators use your component when building an app, whereas app users interact with your component when running an app. Because these two types of users use your component in different ways, there are additional considerations to take into account when designing a custom component as opposed to designing an app.

To provide a good experience for app creators who use your component to build an app:

Provide an interface for users to customize the appearance and behavior of the component in an app by creating public properties.
Enable users to program a response to interactions with the component by creating public callbacks.
Ensure that the component is robust to the different ways in which users can incorporate it into their apps, and provide feedback, such as descriptive error messages, when a user attempts to use it in an unintended way.

To provide a good experience for app users who interact with your component in an app:

Design the component appearance so that users can understand its purpose.
Program the basic behavior of the component so that it is consistent across all apps that use it.

Learn how to create a custom UI component in App Designer by walking through the process of creating a slider-spinner UI component that provides a flexible interface to change a numeric value. When you have completed the process, you will be able to use the slider-spinner component in an App Designer app in the same way you use existing UI components.

You can either create the slider-spinner component by following the interactive tutorial in the App Designer environment or by following the steps on this page.

To run the interactive component tutorial in App Designer, open the App Designer Start Page. In the Custom UI Components section, click Show examples, and then select Interactive Component Tutorial.

App Designer Component Tutorial Steps

This table provides a quick reference for the App Designer interactive component tutorial.

Step Number	Step Instruction
1	Let's build a simple custom UI component that consists of a slider and a spinner with their values connected together. Drag a Slider component onto the canvas.
2	Drag a Spinner component onto the canvas.
3	Create a public property named `Value` to allow app creators to set the slider-spinner component value when they use the component to build an app. Select the component node in the Component Browser and click the button to add a new public property.
4	Fill out the dialog with the following values and then click OK to create the property: Name: `Value` Data Type: `double` Default Value: `0`
5	App Designer has a design view for designing your component and a code view for programming your component. Click Code View to begin programming your component.
6	Create a callback function for the slider to respond when a user changes the slider value. In the Component Browser, right-click `comp.Slider` and select Callbacks > Add ValueChangedFcn callback.
7	When the slider value changes and this callback function is executed, update the `Value` property of your component to match the new slider value. Replace the callback code with the following: comp.Value = event.Source.Value;
8	Next, do the same thing for the spinner. Instead of creating a new callback function, you can reuse the slider callback. In the Component Browser, right-click `comp.Spinner` and select Callbacks > Select existing callback. Then, select the existing callback for the slider from the dialog.
9	Your component's `Value` property now updates when the value of the slider or the spinner changes. Next, conversely, update the slider and spinner value when someone sets your component's `Value` property programmatically. Write the following code to do this in the `update` function, which executes every time the value of a public property changes: comp.Slider.Value = comp.Value; comp.Spinner.Value = comp.Value;
10	Create a public callback to allow users of your component to program a response to an interaction in the context of their app. App Designer creates a public callback when you add an event. Click on the Events tab and then click the button to add a new event.
11	When you add an event, App Designer creates a public callback of the same name with `Fcn` appended. This callback is available when the component is added to an app. Specify the name of the event to be `ValueChanged`.
12	To trigger the `ValueChangedFcn` callback at the right time, you need to notify the event whenever you change your component's `Value` property. Add the following code to the end of the `SliderValueChanged` callback: notify(comp, 'ValueChanged')
13	Click Run to save and run the component to verify the its interactive behavior.
14	To verify that your component's `ValueChangedFcn` callback is triggered when the component value changes, execute the following code in the MATLAB Command Window: comp = tutorialComponent; comp.ValueChangedFcn = @(src,event)disp(src.Value);
15	Congratulations, you just built your first custom UI component! Click Configure to enable your component to appear in the App Designer Component Library. You can use the component in your apps or share it with others.

Create Custom UI Component

To create a custom UI component in App Designer, first open a new blank component. Open the App Designer Start Page, and in the Custom UI Components section, click Blank Component. Save the component file as myComponent.mlapp. Then, follow these steps to build the slider-spinner component with connected values:

Design Component Appearance — Lay out your custom component using existing UI components in App Designer Design View.
Design Component Interface — Provide options for an app creator to customize the appearance and behavior of your custom component to suit the needs of the app. Do this in two steps:
1. Create and Configure Public Properties — Enable the app creator to specify aspects of the component appearance and behavior in an app.
2. Create and Configure Public Callbacks — Enable the app creator to program a response when an app user interacts with the component in an app.
Verify Component Behavior — Ensure your custom component looks and behaves as intended.
Configure Component for Use in Apps — Specify how your custom component appears in the App Designer Component Library.

Design Component Appearance

Design your custom component appearance in Design View.

To design the slider-spinner appearance, first drag a Slider component from the Component Library onto the canvas. Then, drag a Spinner component onto the canvas and position it below the slider.

When you lay out your custom component in Design View, App Designer generates the code that creates the underlying UI components in the setup function in Code View. This function is run once when the custom component object is created in an app. If you have additional startup tasks that you would like to execute once at setup, such as plotting data or initializing default values, you can create a PostSetupFcn callback for the custom component. For more information, see Define Custom UI Component Startup Tasks in App Designer.

Design Component Interface

Design your custom component interface so that an app creator can specify how the component appears and behaves within their app. There are two aspects of the component interface to consider:

Public properties — These are properties of the component that can be set and queried when the component is added to an app. Create public properties to provide component customization options and to expose information about the component to an app creator.
Public callbacks — These are callbacks of the component that can be accessed when the component is added to an app. Create public callbacks to allow an app creator to program a response to a specific component interaction in the context of their app.

Create and Configure Public Properties

To add a public property to your custom component, first create the property and specify its default value, data type, and associated validation functions. Then, write code to connect the property value and the custom component appearance and behavior. Update the public property value when an app user interacts with the component, and update the underlying components when an app creator programmatically sets the public property value.

For the slider-spinner component, create a public property named Value to allow app creators to set the slider-spinner value when they use the component in app. Select the component node in the Component Browser and click the button.

Component Browser. The component node is selected and there is a button to add a new public property.

When you add a new public property, App Designer opens a dialog box that lets you specify property details. Fill out the dialog box with these values:

Name — Enter Value as the property name.
Data Type — Enter double as the property data type.
Default Value — Enter 0 as the default property value.

Click OK to create the property.

Once you create the Value public property, write code to link the property to the slider-spinner component appearance. Navigate to Code View using the button in the upper-right corner of the canvas.

When you create a custom UI component, App Designer creates a class definition file with matlab.ui.componentcontainer.ComponentContainer as the superclass. Use the Code View editor to write code to program your component in this file. Access the custom component object in your code by using comp.

First, update the Value property whenever an app user interacts with the slider or the spinner. Perform this update using these steps:

Create a callback for the slider component. Right-click comp.Slider in the Component Browser and select Callbacks > Add ValueChangedFcn callback.
Update the Value property within the SliderValueChanged callback function. Replace the code in the callback function with this code:
```
comp.Value = event.Source.Value;
```
Assign the same callback function to the spinner component. Right-click comp.Spinner in the Component Browser and select Callbacks > Select existing callback. Use the dialog box to assign the SliderValueChanged function to the spinner ValueChangedFcn callback.

At this point, your code updates the slider-spinner Value property whenever the underlying component values change. Next, conversely, write code to update the underlying spinner and slider components whenever an app creator sets the slider-spinner Value property. Perform this update inside the update function of your component code. The update function executes whenever the value of a public property of the custom component changes, so this ensures that the underlying spinner and slider values always match the value of the custom component.

Add this code to the update function:

comp.Slider.Value = comp.Value;
comp.Spinner.Value = comp.Value;

For more information about creating and configuring public properties, see Create Public Properties for Custom UI Components in App Designer.

Create and Configure Public Callbacks

Create public callbacks for your custom component to enable app creators to write code in their apps to respond to specific interactions. To create a public callback, add an event. An event is a notice that is broadcast when an action occurs. When you add an event for your custom component, App Designer creates a public callback associated with the event. Then, write code to trigger the event, which executes the associated public callback.

In the slider-spinner component, create an event named ValueChanged and write code to trigger the event and execute the associated ValueChangedFcn callback whenever an app user changes the value of the slider or the spinner in a running app. This lets app creators to use the ValueChangedFcn callback in their app. For instance, an app creator might write a callback function to plot some data whenever the app user changes the slider-spinner value.

Use these steps to add and trigger the ValueChanged event:

Select the Event–Callback Pairs tab in the Component Browser and click the button.
In the Add Event–Public Callback Pair dialog box, enter the event name as ValueChanged, and click OK. App Designer creates a public callback of the same name with the letters Fcn appended. So in this case, the public callback is named ValueChangedFcn.
Write code to ensure that the callback is executed at the appropriate moment. Do this by calling the notify function on the component object and specifying the event name. Here, the callback should be executed when an app user interacts with the slider or the spinner. In the SliderValueChanged function, add this code:
```
notify(comp,"ValueChanged")
```

For more information about creating and executing public callbacks, see Create Callbacks for Custom UI Components in App Designer.

Verify Component Behavior

To see what your component looks like in a running app, save the component and then click Run. App Designer displays a UI figure window that contains your custom component.

Run the slider-spinner component, and interact with it to verify that it looks and behaves as expected.

Next, verify that the ValueChangedFcn callback is executed when the component value changes. Create an instance of your component programmatically by specifying the component file name at the MATLAB Command Window and returning the component object as a variable. Enter this code in the Command Window to create a slider-spinner component and assign a callback function:

comp = myComponent;
comp.ValueChangedFcn = @(src,event)disp(src.Value);

Interact with the slider and spinner. The value of the custom component is displayed in the Command Window.

Configure Component for Use in Apps

To use your custom UI component in an App Designer app or to share it for others to use, follow these steps:

In the Designer tab, click Configure for Apps.
Fill out the App Designer Custom UI Component Metadata dialog box, and then click OK.
In the confirmation dialog box, click Add to Path to add the component and generated resources folder to the MATLAB path.
In the Designer tab, click New and select Blank App.

The component appears in the Component Library of the app, under the category specified in the dialog box.

Drag a slider-spinner component onto the canvas. You can set public properties of the component using the Component Browser, and you can assign public callbacks to program the component behavior in the app.

For more information about configuring and sharing your custom UI component, see Configure Custom UI Components for App Designer.