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Manage Code in App Designer Code View

Code View provides most of the same programming features that the MATLAB® Editor provides. It also provides a rich set of features that help you to navigate your code and avoid many tedious tasks. For example, you can search for a callback by typing part of its name in a search bar. Clicking a search result scrolls the editor to the definition of that callback. And if you change the name of a callback, App Designer automatically updates all references to it in your code.

Manage Components, Functions, and Properties

Code View has three panes to help you manage different aspects of your code. This table describes each of them.

Pane NamePane AppearancePane Features
Component Browser

Component Browser showing the property inspector for a button component.

  • Context menu — Right-click a component in the list to display a context menu that has options for deleting or renaming the component, adding a callback, or displaying help. Select the Include Component Labels in Component Browser option to display grouped component labels.

  • Search bar —Quickly locate a component by typing part of its name in the search bar.

  • Component tab — Use this tab to view or change property values for the component that is currently selected. You can also search for a property by typing part of the name in the search bar at the top of this tab.

  • Callbacks tab — Use this tab to manage the callbacks for the component that is selected.

Code Browser

Code Browser showing the Callbacks tab with three callbacks.

  • Callbacks, Functions, and Properties tabs — Use these tabs to add, delete, or rename any of the callbacks, helper functions, or custom properties in your app. Clicking an item in the Callbacks or Functions tab scrolls the editor to the corresponding section in your code. Rearrange the order of callbacks by selecting the callback you want to move and then, drag and drop the callback into its new position in the list. This also repositions the callback in the editor.

  • Search bar — Quickly locate a callback, helper function, or property by typing part of its name in the search bar.

App Layout

App Layout showing a thumbnail of an app that contains a radio button group, a slider and a push button.

  • App thumbnail — Use the thumbnail image to locate components in large, complex apps that have many components. Selecting a component in the thumbnail selects the component in the Component Browser.

Identify Editable Sections of Code

In the Code View editor, some sections of code are editable and some are not. Uneditable sections are generated and managed by App Designer, whereas editable sections correspond to:

  • The body of functions you define (e.g., callbacks and helper functions)

  • Custom property definitions

In the default color scheme, uneditable sections of code are gray and editable sections of code are white.

App code. A properties block and body of a function have a white background, while a methods block and function declaration have a gray background.

Program Your App

App Designer defines your app as a MATLAB class. You do not need to understand classes or object-oriented programming to create an app because App Designer manages those aspects of the code. However, programming in App Designer requires a different workflow than working strictly with functions. You can review a summary of this workflow at any time by clicking the Show Tips button in the Resources tab of the toolstrip.

Manage UI Components

When you add a UI component to your app, App Designer assigns a default name to the component. Use that name (including the app prefix) to refer to the component in your code. You can change the name of a component by double-clicking the name in the Component Browser and typing a new name. App Designer automatically updates all references to that component when you change its name.

Component Browser showing the name of a figure and a button component. The name of the button is app.Button, and the text "Button" is highlighted and editable.

To use the name of a component in your code, you can save some time by copying the name from the Component Browser. Place your cursor in an editable area of the code where you want to add the component name. Then, from the Component Browser, right-click the component name and select Insert at Cursor. Alternatively, you can drag the component name from the list into your code.

Context menu associated with the app.Button component. The context menu includes the Insert at Cursor option.

To delete a component, select its name in the Component Browser and press the Delete key.

Manage Callbacks

To make a component respond to user interactions, add a callback. Right-click the component in the Component Browser and select Callbacks > Add (callback property) callback.

If you delete a component from your app, App Designer deletes the associated callback only if the callback has not been edited and is not shared with other components.

To delete a callback manually, select the callback name in the Callbacks tab of the Code Browser and press the Delete key.

For more information about callbacks, see Callbacks in App Designer.

Share Data Within Your App

To store data, and share it among different callbacks, create a property. For example, if want your app to read a data file and allow different callbacks in your app to access that data, store the data in a property when you load the file.

To create a property, expand the Property drop-down in the Editor tab, and select Private Property or Public Property. App Designer creates a template property definition and places your cursor next to that definition. Change the name of the property as desired.

properties (Access = public)
        X % Average cost

To reference the property in your code, use the syntax app.PropertyName. For example, app.X references the property named X.

For more information about creating and using properties, see Share Data Within App Designer Apps.

Single-Source Code that Runs in Multiple Places

If you want to execute a block of code in multiple parts of your app, create a helper function. For example, you might create a helper function to update a plot after the user changes a number in an edit field or selects an item in a drop-down list. Creating a helper function allows you to single-source the common commands and avoid having to maintain redundant sets of code.

To add a helper function, expand the Function drop-down in the Editor tab, and select Private Function or Public Function. App Designer creates a template function and places your cursor in the body of that function.

To delete a helper function, select the function name in the Functions tab of the Code Browser and press the Delete key.

For more information about writing helper functions, see Reuse Code Using Helper Functions.

Create Input Arguments

To add input arguments to your app, click App Input Arguments in the Editor tab. Input arguments are commonly used for creating apps that have multiple windows. For more information, see Startup Tasks and Input Arguments in App Designer.

Add Help Text for Your App

Add an app summary and description to provide information about your app to users. To add help text or to edit existing help text, click App Help Text . Use the App Help Text dialog box to specify a short summary of the app and a more detailed explanation of what the app does and how to use it. App Designer adds this help text as a comment under the app definition statement.

To display app help text in the MATLAB Command Window, call the help function and specify the app name. In addition, app help text appears at the top of the documentation page for your app. You can view the documentation page for your app by calling the doc function and specifying the app name.

Limit Your App to Only One Running Instance at a Time

When you create an app in App Designer you have the option to select between two run behaviors for the app:

  • Allow only a single running instance of the app at a time.

  • Allow multiple instances of the app to run at the same time. This is the default behavior.

To change the run behavior of your app, select the app node from the Component Browser. Then, from the Code Options section of the App tab, select or clear Single Running Instance.

Component Browser Inspector for the app node. The Code Options section is expanded and shows the Single Running Instance check box.

When Single Running Instance is selected and you run the app multiple times, MATLAB reuses the existing instance and brings it to the front rather than creating a new one. When this option is cleared, MATLAB creates a new app instance each time you run it and continues to run the existing instances. These run behaviors apply to apps that you run from the Apps tab on the MATLAB Toolstrip or from the Command Window.

When you run apps from App Designer their behavior doesn't change whether this option is selected or cleared. App Designer always closes the existing app instance before creating a new one.

Fix Code Problems and Run-Time Errors

Like the MATLAB Editor, the Code View editor provides Code Analyzer messages to help you discover errors in your code.

Code Analyzer message for an edit field callback. The code in the function body sets EditField.Value. The message says "Use app.EditField to reference a property of app" and includes a button labeled "Fix".

If you run your app directly from App Designer (by clicking Run ), App Designer highlights the source of errors in your code, should any errors occur at run time. To hide the error message, click the error indicator (the red circle). To make the error indicator disappear, fix your code and save your changes.

Error message. The line of code with the error has an error indicator next to it.

You can also diagnose problems in your code by debugging your app code interactively in App Designer. For more information, see Debug MATLAB Code Files.

Personalize Code View Appearance

You can customize how your code appears in the Code View editor. To change your code view preferences, go to the Home tab of the MATLAB Desktop. In the Environment section, click Preferences.

Change Color Settings

To change the color settings for editable sections of code and to customize syntax highlighting, select MATLAB > Colors and adjust the desktop tool colors and the MATLAB syntax highlighting colors. These settings affect both the App Designer Code View editor and the MATLAB Editor. For more information, see Change Desktop Colors.

To change the background color of uneditable sections of code, select MATLAB > App Designer and adjust the read-only background color. This setting can be changed only if the Use system colors option in MATLAB > Color Preferences is unchecked.

Change Tab Preferences

To specify the size of tabs and indents in the Code View editor, select MATLAB > Editor/Debugger > Tab. From here, you can specify the size of tabs and indents, as well as details about how tabs behave. These preferences affect both the App Designer Code View editor and the MATLAB Editor. For more information, see Editor/Debugger Tab Preferences.

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