Clearing a Figure in MATLAB App Designer: A Comprehensive Guide

MATLAB App Designer is a powerful tool that allows users to create professional apps with a rich user interface. One of the common tasks while developing an app is updating and refreshing plots or figures. In many cases, you may need to clear a figure to reset the visual space or remove old data before plotting new information. This guide will provide a detailed explanation on how to effectively clear a figure in MATLAB App Designer, including methods and best practices to ensure your app runs smoothly.

Understanding MATLAB Figures in App Designer

MATLAB figures are graphical windows where data can be visualized. In App Designer, these figures are usually embedded within the app's user interface (UI) and are often updated dynamically as the app runs. For example, you might have an app that plots data from a simulation or a dataset that the user can modify in real time.

When dealing with dynamic data, clearing the figure before plotting new data is essential to prevent overlaying or cluttering, which can lead to confusion or misinterpretation of the visualized data.

Methods to Clear a Figure

MATLAB provides several methods to clear a figure, and choosing the right one depends on the specific needs of your app. Below are some common approaches:

1. Using cla Function:
   The cla function clears the current axes. It removes all graphics objects from the axes but leaves the axes intact. This is useful when you want to reset the plot without removing the axes, labels, or titles.

   matlab
   cla(app.UIAxes); % Where 'UIAxes' is the name of your axes component
   

2. Using clf Function:
   The clf function clears the entire figure, removing all axes, labels, and other components. This is useful when you want to completely reset the figure and start from scratch.

   matlab
   clf(app.UIFigure); % Where 'UIFigure' is the name of your figure component
   

3. Using delete Method:
   The delete method can be used to remove specific objects from a figure. This method is more selective and allows you to clear only certain plots or UI components without affecting others.

   matlab
   delete(findall(app.UIFigure,'type','line')); % Deletes only line objects from the figure
   

4. Setting Visible Property to Off and On:
   Sometimes, instead of clearing, you might want to hide the figure temporarily and then display a new plot. This can be done by toggling the Visible property.

   matlab
   app.UIAxes.Visible = 'off';
   app.UIAxes.Visible = 'on';
   

Best Practices for Clearing Figures in App Designer

To ensure smooth performance and user experience, consider the following best practices when clearing figures in MATLAB App Designer:

• Minimize Flickering: Repeatedly clearing and redrawing figures can cause flickering, which may be distracting to users. To minimize this, consider using double buffering techniques or only updating parts of the figure that need to change.

• Preserve User Settings: If your app allows users to customize aspects of the figure (e.g., zoom level, axis limits), try to preserve these settings when clearing the figure. This can be achieved by storing the settings before clearing and reapplying them afterward.

• Handle Large Data Efficiently: When dealing with large datasets, clearing and redrawing the figure can be time-consuming. To improve efficiency, consider using techniques like downsampling the data or plotting only a subset of the data that fits the user's current view.

Example: A Complete Workflow

Let's walk through an example where we create a simple app that allows users to plot data and clear the figure before plotting new data.

matlab
function startupFcn(app)
    % Initialize the UI and plot a sine wave
    x = linspace(0, 2*pi, 100);
    y = sin(x);
    plot(app.UIAxes, x, y);
end

function ClearPlotButtonPushed(app, event)
    % Clear the current plot when the 'Clear Plot' button is pushed
    cla(app.UIAxes); % Clears the axes without deleting the UIAxes
end

function NewPlotButtonPushed(app, event)
    % Plot a new cosine wave
    x = linspace(0, 2*pi, 100);
    y = cos(x);
    plot(app.UIAxes, x, y);
end

In this example, the ClearPlotButtonPushed function clears the current plot, and the NewPlotButtonPushed function plots new data. This ensures that each time the user clicks the "New Plot" button, the figure is cleared, and the new data is displayed without any overlap.

Conclusion

Clearing figures in MATLAB App Designer is a crucial aspect of creating dynamic and responsive applications. By understanding the different methods available and implementing best practices, you can ensure that your app handles figure updates efficiently and provides a smooth user experience. Whether you are developing a simple plotting tool or a complex data analysis app, mastering figure management will significantly enhance the usability and performance of your MATLAB apps.