Implementing Check-in time chart in Orga App

Earlier in the Open event orga app there were no charts present to track the check-in time of the attendees. Hence it was quite cumbersome for the organiser to track the people and at what time they have checked-in. Using this feature of check-in time chart, the process has become quite easier.

Whenever an attendee checks-in, the data point is added to the chart and a chart is plotted. The Y-axis shows the number of attendees and the X-axis shows the time at which they have checked-in.

To implement this feature I have taken use of the MPAndroidCharts library which makes the job a lot easier. Following steps were followed to implement the charts:

  • Adding the following Library dependency in the build.gradle file
implementation “com.github.PhilJay:MPAndroidChart:v3.0.3”
  • Now the following code is added to the ticket_analytics.xml file. This is done so that the UI of the charts can be created. The following XML file consists of the LineChart XML tag which shows the check-in time chart on screen. Also the labelling of the axis needs to be done, so the X-axis is explicitly named as “TIME”.

      android:textSize=“@dimen/text_size_small” />

      android:layout_marginStart=“@dimen/spacing_normal” />

      android:textSize=“10sp” />


          android:background=“@color/color_shadow” />

          android:background=“@color/color_bottom_surface” />
  • Now the a method loadCheckIn( )  chart needs to added to the EventsDashboardPresenter. This is called from the EventsDashboardFragment. The loadDataCheckIn( ) is created in the ChartAnalyzer class. We pass getId( ) as the parameter.
private void loadCheckInTimesChart() {
      .subscribe(() -> {
      }, throwable -> getView().showChartCheckIn(false));
  • Now we add the method loadDataCheckIn( ) in the ChartAnalyzer class. This method returns a Completable and takes eventId as the single parameter.
public Completable loadDataCheckIn(long eventId) {
  isCheckinChart = true;
  return getAttendeeSource(eventId).doOnNext(attendee -> {
     String checkInTime = attendee.getCheckinTimes();
     int length = checkInTime.split(“,”).length;
     String latestCheckInTime = checkInTime.split(“,”)[length – 1];
     error = checkInTime == null ? true : false;
     addDataPointForCheckIn(checkInTimeMap, latestCheckInTime);
    .doAfterSuccess(attendees -> this.attendees = attendees)
    .doOnComplete(() -> {
        if (error)
            throw new IllegalAccessException(“No checkin’s found”);
        checkInDataSet = setDataForCheckIn(checkInTimeMap, “check-in time”);

It calls the getAttendeeSource( ) which further gives a call to the method getAttendees( ) from the AttendeeRepository. All the inormation related to the attendees is returned from which the check-in times is extracted. The check-in times are returned in comma separated form and hence we need to extract the first element of the sequence.

private Observable<Attendee> getAttendeeSource(long eventId) {
  if (attendees == null || attendees.isEmpty())
      return attendeeRepository.getAttendees(eventId, false);
      return Observable.fromIterable(attendees);
  • After the success of loading the attendees, the method addDataPointForCheckIn is called. We call it by inserting the parameters Map<Integer, Long> and the dateString which we had passed from the loadDataCheckIn( ). Following is the code for it. A map is created out of the data. The key in the map is the time and value is the number of people who have checked-in at that time.
private void addDataPointForCheckIn(Map<Integer, Long> map, String dateString) {
  int hour = DateUtils.getDate(dateString).getHour();
  Long numberOfCheckins = map.get(hour);

  if (numberOfCheckins == null)
      numberOfCheckins = 0L;

  map.put(hour, ++numberOfCheckins);
  • After the map is created it is passed on to the setDataForCheckIn( ) and the label is provided as “check-in times”. Following is the code for setDataForCheckIn( ). All the values of the map are parsed and a new entry object is made in which the value of the key and value pairs are passed. This object is then added to the ArrayList.
private LineDataSet setDataForCheckIn(Map<Integer, Long> map, String label) throws ParseException {
  List<Entry> entries = new ArrayList<>();
  for (Map.Entry<Integer, Long> entry : map.entrySet()) {
      entries.add(new Entry(entry.getKey(), entry.getValue()));
  Collections.sort(entries, new EntryXComparator());

  // Add a starting point 2 hrs ago
  entries.add(0, new Entry(entries.get(0).getX() – 2, 0));
  return new LineDataSet(entries, label);
  • The object LineDataSet is returned with all the entries stored in the ArrayList. Now the prepare( ) is called. It is in this method that we add the code for the UI of the chart.
private void prepare() {
  if (isCheckinChart) {
      initializeLineSet(checkInDataSet, R.color.light_blue_500, R.color.light_blue_100);
  } else {
      initializeLineSet(freeSet, R.color.light_blue_500, R.color.light_blue_100);
      initializeLineSet(paidSet, R.color.purple_500, R.color.purple_100);
      initializeLineSet(donationSet, R.color.red_500, R.color.red_100);

initializeLineSet( ) is the method where we add the color which will be used for plotting the data set.In our case the color is blue.

  • We also need to plot the time stamps in the X-axis. Unfortunately MPAndroidCharts doesn’t have a functionality for that. So to handle it an inner class MyMyAxisValueFormatter is created which extends IAxisValueFormatter. Following is the code for it.
public class MyAxisValueFormatter implements IAxisValueFormatter {

  public String getFormattedValue(float value, AxisBase axis) {
      if (value < 0)
          return values[24 + (int) value];
      return values[(int) value];

The values array list consists of the time stamps that will be present on the X-Axis.

String[] values = new String[] {“00:00”, “1:00”, “2:00”, “3:00”, “4:00”, “5:00”, “6:00”, “7:00”, “8:00”, “9:00”, “10:00”, “11:00”, “12:00”, “13:00”, “14:00”, “15:00”, “16:00”, “17:00”, “18:00”, “19:00”, “20:00”, “21:00”, “22:00”, “23:00”};
  • Finally the showChart( ) is called in which we specify details regarding the grid color, legend, visibility of X and Y axis etc. We also specify the animation that needs to be done whenever the chart is on screen.


public void showChart(LineChart lineChart) {

  YAxis yAxis = lineChart.getAxisLeft();
  if (!isCheckinChart)
      if (maxTicketSale > TICKET_SALE_THRESHOLD)
          yAxis.setGranularity(maxTicketSale / TICKET_SALE_THRESHOLD);
  else {
      XAxis xAxis = lineChart.getXAxis();
      xAxis.setValueFormatter(new MyAxisValueFormatter());

  Description description = new Description();


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Coloring Waveforms in PSLab Charts

Charts are used to display set of data in an analytical manner such that an observer can easily come to a conclusion by just looking at it without having to go through all the numerical data sets. Legends are used to differentiate a set of data set from another set. Generally, different colors and different names are used to form a legend in a chart.

MPAndroidChart is an amazing library with the capability of generating different types of graphs in an Android device. In PSLab several user interfaces are implemented using LineCharts to display different waveforms such as readings from channels attached to PSLab device, logic levels etc.

When several data sets are being plotted on the same graph area, legends are used. In PSLab Android application, Oscilloscope supports four different type of waveforms to be plotted on the same graph. Logic Analyzer implements one to four different types of logic level waveforms on the same plot. To identify which is which, legends with different colors can be used rather than just the names. For the legends to have different colors, it should be explicitly set which color should be held by which data set. Otherwise it will use the default color to all the legends making it hard to differentiate data lines when there are more than one data set is plotted.

Assume a data set is generated from a reading taken from a probe attached to PSLab device. The set will be added as an Entry to an array list as follows;

ArrayList<Entry> dataSet = new ArrayList<Entry>();

The next step will be to create a Line Data Set

LineDataSet lineData = new LineDataSet(dataSet, "DataSet 1");

This LineDataSet will contain sample values of the waveform captured by the microprocessor. A LineDataSet object support many methods to alter its look and feel. In order to set a color for the legend, setColor() method will be useful. This method accepts an integer as the color. This method can be accessed as follows;


MPAndroidChart provides different sets of colors under ColorTemplate. This class has several predefined colors with five colors in each color palette are added by the developers of the library and they can be accessed using the following line of code by simply calling the index value of the palette array list.


Set of color palettes available in the ColorTemplate class are;


The following demonstrates how the above activities produce a line chart with three different data sets with different colored legends.

This implementation can be used to enhance the readability of the waveforms letting user being able to differentiate between one waveform from another in PSLab Android application.


PSLab official web site:

Continue ReadingColoring Waveforms in PSLab Charts