How to work with MPAndroidChart? – Neurolab Memory graph program mode

Memory graph mode

Overview

In Android App development, implementation of Android Charts play an integral part in developing database oriented apps, be it casual or professional apps.

Data Analysis plays an integral part in various sectors and industries in today’s world. In sports, e.g- cricket, we see the use of charts like bar charts, line charts in various stages of the game to present the game and score analysis.

In healthcare, we see the use of live real time graphs to show human health analysis like the heart rate, brain waves, etc. In the IT industry, professionals use graphical data analysis for their presentations in meetings and conferences.

I have been working with FOSSASIA on the Neurolab Android App, where I had to work on this unique program mode called “Memory Graph” wherein I had to work extensively with MPAndroidChart library. While working, I understood the various use cases of charts and graphs on the Android platform. In this blog, I want to showcase the building of one part of the app with a proper tutorial.

Tutorial

In the Android SDK, we, the developers have been given the benefit of a tool known as GraphView. But this view being a very default and basic tool in the toolkit, has limitations in terms of customization, needs a lot of boilerplate code to set up the base to work upon.

Also plotting real time graphs becomes a challenge while using the GraphView.

In this tutorial, we will be focusing on the Memory Graph program mode of the app wherein we will be using an external library – MPAndroidChart to help us achieve our aim.

                                                        Memory Graph

      1. Firstly, open the app level build.gradle and implement the library dependency in there.

                 implementation ‘com.github.PhilJay:MPAndroidChart:v3.1.0’

         Note – The library version may change depending upon the time you are reading     this blog. Refer here for the latest library updates.

XML layout

1. The layout for our chart screen should be simple without any other components on the screen so that it is perfectly comfortable for the users to understand the graph and not get overwhelmed. Here, we are going to use a RelativeLayout as the parent to the Chart. For our Memory graph program mode, I worked with the LineChart view from the MPAndroidChart library. The xml code for the layout:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.github.mikephil.charting.charts.LineChart
        android:id="@+id/brain_chart"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</RelativeLayout>

Layout binding and Java code

1. In the onCreate method of our MemoryGraph Activity, we set the layout parameters as flags for our chart layout to use of the screen window. We find the LineChart from the layout by its id and bind it up using the private variable which is going to be used to set it up programmatically. Here is the code for the onCreate method:

private LineChart graph;
    private Thread thread;

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fragment_memory_graph);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);
        graph = findViewById(R.id.mem_graph);
    }

2. We are going to create a method named initGraph to set up the graph and make it ready to plot the data in real-time. Here is the code for the method:

graph.setOnChartValueSelectedListener(this);                // enable description text
        graph.getDescription().setEnabled(true);

        // enable touch gestures
        graph.setTouchEnabled(true);

        // enable scaling and dragging
        graph.setDragEnabled(true);
        graph.setScaleEnabled(true);
        graph.setDrawGridBackground(false);

        // if disabled, scaling can be done on x- and y-axis separately
        graph.setPinchZoom(true);

        // set an alternative background color
        graph.setBackgroundColor(getResources().getColor(R.color.memory_graph_background));

        LineData data = new LineData();
        data.setValueTextColor(Color.WHITE);

        // add empty data
        graph.setData(data);

        graph.getDescription().setText(getResources().getString(R.string.axis_desc_time));
        graph.getDescription().setTextColor(Color.WHITE);

        // get the legend (only possible after setting data)
        Legend l = memGraph.getLegend();

        // modify the legend ...
        l.setForm(Legend.LegendForm.LINE);
        l.setTextColor(Color.WHITE);

        XAxis xl = graph.getXAxis();
        xl.setTextColor(Color.WHITE);
        xl.setDrawGridLines(false);
        xl.setAvoidFirstLastClipping(true);
        xl.setEnabled(true);

        YAxis leftAxis = graph.getAxisLeft();
        leftAxis.setTextColor(Color.WHITE);
        leftAxis.setAxisMaximum(100f);
        leftAxis.setAxisMinimum(0f);
        leftAxis.setDrawGridLines(true);
        leftAxis.setGridColor(Color.WHITE);

        YAxis rightAxis = graph.getAxisRight();
        rightAxis.setEnabled(false);

Now, in here to use the setOnChartValueSelectedListener callback we need to implement the OnChartValueSelectedListener interface in our Activity. This will be required if the user clicks on a plot point. We need to set up the chart to respond to that user click on a particular data value on the chart.

3. Next, we are going to create a set of data for our graph to work with. As this set we create will be worked on by LineChart, hence our set will be of type LineDataSet. Using this LineDataSet, we will be able to set the axes labels, description, axes dependency (left or right), graph background, graph line colors and other necessary details. All parameters which can be tweaked through the `LineDataSet` for a LineGraph can be found here.

Here is the code for creating the LineDataSet :

private LineDataSet createSet() {

        LineDataSet set = new LineDataSet(null, "Brain waves");
        set.setAxisDependency(YAxis.AxisDependency.LEFT);
        set.setColor(Color.GREEN);
        set.setCircleColor(Color.WHITE);
        set.setLineWidth(2f);
        set.setCircleRadius(4f);
        set.setFillAlpha(65);
        set.setFillColor(Color.GREEN);
        set.setHighLightColor(Color.rgb(244, 117, 117));
        set.setValueTextColor(Color.WHITE);
        set.setValueTextSize(9f);
        set.setDrawValues(false);
        return set;
    }

4. Now, that we have set up the data for our LineChart to be used, we would be moving on to plotting the data. Since, everybody would not be able to have datasets containing brain-wave data, we would be taking the help of the ‘random’ function provided in Java. We create a function called `addEntry()`, wherein we add a new ‘Entry’ to the data set. Here, as we are working with a single dataset (the set of random values), the index for our dataset in the LineChart, will be zero.

private void addEntry() {

        LineData data = graph.getData();

        if (data != null) {

            ILineDataSet set = data.getDataSetByIndex(0);

            if (set == null) {
                set = createSet();
                data.addDataSet(set);
            }

            data.addEntry(new Entry(set.getEntryCount(), (float) (Math.random() * 40) + 30f), 0);
            data.notifyDataChanged();

            // let the graph know it's data has changed
            graph.notifyDataSetChanged();

            // limit the number of visible entries
            graph.setVisibleXRangeMaximum(120);

            // move to the latest entry
            graph.moveViewToX(data.getEntryCount());

        }
    }

5. We then create data feeding function called ‘feedMultiple’, for the chart. It contains a new runnable, which calls the ‘addEntry’ function. We then execute that runnable in a UI thread from within a for-loop, thus creating continuous values to plot. Here is the code for the ‘feedMultiple’ function;

private void feedMultiple() {

        if (thread != null)
            thread.interrupt();

        final Runnable runnable = () -> addEntry();

        thread = new Thread(() -> {
            for (int i = 0; i < 1000; i++) {

                // Don't generate garbage runnables inside the loop.
                runOnUiThread(runnable);

                try {
                    Thread.sleep(25);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });

        thread.start();
    }

6. Now we can call our ‘feedMultiple’ method from the onCreate function of our MemoryGraph Activity java file and we are good to go!

The full code for Memory Graph Mode can be found here: https://github.com/fossasia/neurolab-android/blob/development/app/src/main/java/io/neurolab/fragments/MemoryGraphFragment.java

Hope this blog helps you strengthen your Android development skills.

Resources

  1. Author – Amar, Article – Working with MPAndroidChart, Source – Code your world, Date – July 2016, Website – https://coderzduniya.blogspot.com/2016/07/working-with-mpandroidchart-how-to.html

2. Author – PhilJay, Source – Github, Library – MPAndroidChart Library, Website – https://github.com/PhilJay/MPAndroidChart/

Tags: FOSSASIA, GSOC19, Neurolab, Android, Graphs, Open-source

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