How to Close a MATLAB App Using App Designer

In MATLAB App Designer, closing an app programmatically involves using the built-in delete function. This function can be triggered through various callbacks depending on the specific requirements of your application. The CloseRequestFcn callback is one of the most common methods to handle app closure. Below is a detailed guide on how to implement this callback to ensure a smooth and controlled app shutdown.

Understanding CloseRequestFcn

The CloseRequestFcn callback is executed when the user attempts to close the app using the window's close button (the "X" button in the top-right corner of the window). By defining this callback, you can control what happens when the app is closed. This is useful for saving data, prompting the user to save their work, or performing other cleanup tasks.

Step-by-Step Guide to Implement CloseRequestFcn

1. Open Your App in App Designer: Start by opening your app project in MATLAB App Designer.

2. Access the Code View: Switch to the Code View where you can see the app’s callbacks and other code elements.

3. Define the CloseRequestFcn Callback: Locate the CloseRequestFcn property in the app's component browser. If it does not exist, you can create it. Here’s an example of how you might define this callback:

   matlab
   function closeApp(app, event)
       % Code to execute when the app is requested to close
       % Example: Save data or prompt user to save
   
       % Prompt user to save changes
       selection = uiconfirm(app.UIFigure, 'Do you want to save changes before closing?', 'Save Changes', 'Options', {'Save', 'Discard', 'Cancel'}, 'DefaultOption', 1, 'CancelOption', 3);
   
       % Handle user response
       switch selection
           case 'Save'
               % Call a method to save data
               app.saveData();
               delete(app);
           case 'Discard'
               delete(app);
           case 'Cancel'
               % Do nothing, app remains open
       end
   end
   

4. Attach the Callback to the App’s UIFigure: Ensure that the CloseRequestFcn is assigned to the app’s main figure. This can be done in the properties panel of the UIFigure or programmatically in the app’s startup function:

   matlab
   % In the startup function or constructor
   app.UIFigure.CloseRequestFcn = @(src, event) closeApp(app, event);
   

5. Test the Callback: Run your app and test closing it using the close button. Ensure that the callback executes as expected and that your app handles user responses correctly.

Additional Considerations

• Saving Data: If your app deals with important data, ensure that the saveData method or similar functionality is robust and handles different data types and scenarios.

• User Prompts: When prompting users, make sure the messages are clear and the options are straightforward to avoid confusion.

• Cleanup: Ensure that any resources or open files are properly closed or saved to prevent data loss or corruption.

Example of Usage

Assume you have an app with a text editor feature. When the user tries to close the app, you might want to prompt them to save their work. The provided callback example will prompt the user with options to save, discard, or cancel the closure. This approach ensures that users do not accidentally lose their unsaved changes.

Conclusion

Implementing a controlled app closure process in MATLAB App Designer using the CloseRequestFcn callback allows you to manage how your app shuts down. Whether it’s saving data, prompting users, or performing cleanup tasks, this callback provides a flexible way to handle the closing process gracefully.

By following the steps outlined above, you can ensure that your app behaves as expected when users attempt to close it, providing a better user experience and safeguarding important data.