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Organize App Data Using MATLAB Classes

As the size and complexity of an app increases, it can be difficult to organize and manage the code to perform calculations, process data, and manage user interactions in one file. This example shows how to take an app created entirely in App Designer and reorganize the app code into two parts:

  • Code that stores your app data and the algorithms to process that data, implemented as a MATLAB® class

  • Code that displays the app and manages user interactions, implemented as an App Designer app

Separating the data and algorithms from the app has multiple benefits.

  • Scalability — It is easier to extend app functionality when the code is organized into multiple self-contained portions.

  • Reusability — You can reuse your data and algorithms across multiple apps with minimal effort.

  • Testability — You can run and test your algorithms in MATLAB, independently from the app.

This example uses the PulseGenerator app, which lets users specify options to generate a pulse and visualize the resulting waveform. The goal of the example is to reorganize the code in the original app by performing these steps:

  1. Create a Pulse class that stores pulse data, such as the type, frequency, and length of the pulse, and the algorithm used to take that pulse data and generate the resulting waveform.

  2. Modify the code in App Designer to use the Pulse class to perform calculations and to update the app display.

In the final app, when a user interacts with the app controls, the code in App Designer updates the data stored in the Pulse class and calls a class method to generate the waveform data. App Designer then updates the app display with the new waveform visualization.

How a user interaction is processed in the App Designer code and the Pulse class

To view and run the final app, see Pulse Generator App That Stores Data in a Class.

Open App Designer App

Run this command to open a working copy of the PulseGenerator app.

openExample('matlab/PulseGeneratorAppExample')
Use this app as a starting point as you modify and reorganize the app code.

Write a MATLAB Class to Manage App Data

Separating the data and algorithms that are independent of the app interface allows you to organize the different tasks that your code performs, and to test and reuse these tasks independently of one another. Implementing this portion of your app as a MATLAB class has these benefits:

  • You can manage a large amount of interdependent data using object-oriented design.

  • You can easily share and update this data within your App Designer app.

For more information about the benefits of object-oriented design in MATLAB, see Why Use Object-Oriented Design.

Define Class

To determine which aspects of your app to separate out as a class, consider what parts of your app code do not directly impact the app user interface, and which parts of your app you might want to test separately from the running app.

In the pulse generator app, the app data consists of the pulse that the user wants to visualize. Create a new class file named Pulse.m in the same folder as the PulseGenerator.mlapp app file. Define a handle class named Pulse by creating a classdef block.

classdef Pulse < handle
% ...
end

Store your app data and write functions to implement your app algorithms within the classdef block.

Create Properties

Use properties to store and share app data. To define properties, create a properties block. Create properties for data that the app needs access to and for data that is processed by algorithms associated with the app.

In the Pulse class, create a properties block to hold the data that defines a pulse, such as the pulse type and the frequency and length of the pulse.

    properties
        Type
        Frequency
        Length
        Edge 
        Window
        Modulation
        LowPass
        HighPass
        Dispersion
    end

    properties (Constant)
        StartFrequency = 10;
        StopFrequency = 20;
    end

For more information about defining properties in a class, see Property Syntax.

Create Functions

Define functions that operate on the app data in a methods block in the class definition.

For example, the original PulseGenerator app has a function defined in App Designer named generatePulse that computes a pulse based on the pulse properties. Because this algorithm does not need to update the app display or directly respond to user interaction, you can move the function definition from App Designer into the Pulse class.

Create a methods block and copy the generatePulse function definition into the block. To keep the class definition independent of the app, update the references to UI component values in the app to instead query the values of Pulse object properties using the syntax obj.Property. The beginning of your function definition should look like this:

    methods
        function result = generatePulse(obj)
            
            type = obj.Type;
            frequency = obj.Frequency;
            signalLength = obj.Length;
            edge = obj.Edge;
            window = obj.Window;
            modulation = obj.Modulation;
            lowpass = obj.LowPass;
            highpass = obj.HighPass;
            dispersion = obj.Dispersion;
            
            startFrequency = obj.StartFrequency;
            stopFrequency = obj.StopFrequency;
            
            t = -signalLength/2:1/frequency:signalLength/2;
            sig = (signalLength/(8*edge))^2;
            
            switch type
               % The rest of the code is the same as the original
               % function in the PulseGenerator app.
               % ...
        end
    end

To view the complete function code, see Pulse Generator App That Stores Data in a Class.

For more information about writing class methods, see Define Class Methods and Functions.

Test Algorithm

One of the benefits of storing app data in a class is that you can interact with the data object and test your algorithms independently the running app.

For example, create a Pulse object and set its properties in the Command Window.

p = Pulse;
p.Type = 'gaussian';
p.Frequency = 500;
p.Length = 2;
p.Edge = 1;
p.Window = 0;
p.Modulation = 0;
p.LowPass = 0.4;
p.HighPass = 0;
p.Dispersion = 0;

Call the generatePulse method of the Pulse object p. Visualize the pulse in a plot.

step = 1/p.Frequency;
xlim = p.Length/2;
x = -xlim:step:xlim;
y = generatePulse(p);
plot(x,y);

Plot of a Gaussian pulse

You can also test your algorithm using a testing framework. For more information, see Ways to Write Unit Tests.

Share Data with App

To access the data object from within App Designer, create an instance of the class in your App Designer code and store it in a property of your app. You can set and query the object properties that store the data and call the class functions to process the data in response to user interactions.

In the PulseGenerator app in App Designer, create a new private property by clicking the Property button in the Editor tab. Add a private property named PulseObject to hold the Pulse object.

Then, in the StartupFcn for the app, create a Pulse object by adding this code to the top of the function definition.

app.PulseObject = Pulse;

To generate the pulse for visualization when a user interacts with one of the controls in the app, modify the updatePlot function. This function is called in multiple callback functions of the PulseGenerator app, whenever the user interacts with one of the controls in the app.

In the updatePlot function, first set the properties of the app.Pulse object using the values of the app controls by adding this code to the top of the function.

app.PulseObject.Type = app.TypeDropDown.Value;
app.PulseObject.Frequency = app.FrequencyEditField.Value;
app.PulseObject.Length = app.SignalLengthsEditField.Value;
app.PulseObject.Edge = app.EdgeKnob.Value;
app.PulseObject.Window = app.WindowKnob.Value;  
app.PulseObject.Modulation = str2double(app.ModulationKnob.Value);
app.PulseObject.LowPass = app.LowPassKnob.Value;
app.PulseObject.HighPass = app.HighPassKnob.Value;
app.PulseObject.Dispersion = str2double(app.DispersionKnob.Value);

Then, update the call to the generatePulse function by replacing the input argument with app.PulseObject.

p = generatePulse(app.PulseObject);

Finally, ensure that the app calls the newly defined generatePulse function in the Pulse class by deleting the generatePulse function that is defined in App Designer.

To view the complete app code, see Pulse Generator App That Stores Data in a Class.

Pulse Generator App That Stores Data in a Class

This example shows the final PulseGenerator app, with the app data and algorithms implemented separately in the Pulse class. Run the example by clicking the Run button in App Designer.

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