Pass RolloverModifier data points to a ViewModel

Overview

This documentation provides a complete working example showing how to:

Intercept RolloverModifier events
Extract Series info during hover interactions
Pass the Series info to another ViewModel

Implementation

1. ViewModel

Kotlin
Java

class ChartViewModel : ViewModel() {
    private val _rolloverData = MutableLiveData<String>()
    val rolloverData: LiveData<String> = _rolloverData

    // Call this method when you detect rollover changes
    fun onRolloverChanged(seriesName: String, xValue: String, yValue: String) {
        val data = "$seriesName: X=$xValue, Y=$yValue"
        _rolloverData.value = data
    }
}

public class ChartViewModel extends ViewModel {
    private final MutableLiveData<String> rolloverData = new MutableLiveData<>();

    public LiveData<String> getRolloverData() {
        return rolloverData;
    }

    // Call this method when you detect rollover changes
    public void onRolloverChanged(String seriesName, String xValue, String yValue) {
        String data = seriesName + ": X=" + xValue + ", Y=" + yValue;
        rolloverData.setValue(data);
    }
}

2. Activity

Kotlin
Java

// Custom series info provider class to get the rollover modifier data points
private class CustomSeriesInfoProvider(
    private val chartViewModel: ChartViewModel
) : DefaultXySeriesInfoProvider() {

    override fun getSeriesTooltipInternal(
        context: Context,
        seriesInfo: XySeriesInfo<*>,
        modifierType: Class<*>
    ): ISeriesTooltip {
        return CustomXySeriesTooltip(context, seriesInfo, "RolloverModifier", chartViewModel)
    }

    private class CustomXySeriesTooltip(
        context: Context,
        seriesInfo: XySeriesInfo<*>,
        private val modifierName: String,
        private val chartViewModel: ChartViewModel
    ) : XySeriesTooltip(context, seriesInfo) {

        override fun internalUpdate(seriesInfo: XySeriesInfo<*>) {
            val sb = SpannableStringBuilder()
            sb.append("X: ").append(seriesInfo.formattedXValue).append(StringUtil.NEW_LINE)
            sb.append("Y: ").append(seriesInfo.formattedYValue).append(StringUtil.NEW_LINE)

            chartViewModel.onRolloverChanged("Series 1", seriesInfo.formattedXValue.toString(), seriesInfo.formattedYValue.toString())

            seriesInfo.seriesName?.let { name ->
                val start = sb.length
                sb.append(name)
                sb.setSpan(
                    ForegroundColorSpan(ColorUtil.White),
                    start,
                    sb.length,
                    Spanned.SPAN_EXCLUSIVE_EXCLUSIVE
                )
                sb.append(StringUtil.NEW_LINE)
            }

            sb.append(modifierName)
            text = sb
            setSeriesColor(0xff6495ed.toInt())
        }
    }
}


// Custom series info provider class to get the rollover modifier data points
private static class CustomSeriesInfoProvider extends DefaultXySeriesInfoProvider {

    private final ChartViewModel chartViewModel;

    public CustomSeriesInfoProvider(ChartViewModel chartViewModel) {
        this.chartViewModel = chartViewModel;
    }

    @Override
    protected ISeriesTooltip getSeriesTooltipInternal(Context context, XySeriesInfo<?> seriesInfo, Class<?> modifierType) {
        return new CustomXySeriesTooltip(context, seriesInfo, "RolloverModifier",chartViewModel);
    }

    private static class CustomXySeriesTooltip extends XySeriesTooltip {
        private final String modifierName;
        private final ChartViewModel chartViewModel;

        public CustomXySeriesTooltip(Context context, XySeriesInfo<?> seriesInfo, String modifierName, ChartViewModel chartViewModel) {
            super(context, seriesInfo);
            this.modifierName = modifierName;
            this.chartViewModel = chartViewModel;
        }

        @Override
        protected void internalUpdate(XySeriesInfo seriesInfo) {
            final SpannableStringBuilder sb = new SpannableStringBuilder();
            sb.append("X: ").append(seriesInfo.getFormattedXValue()).append(StringUtil.NEW_LINE);
            sb.append("Y: ").append(seriesInfo.getFormattedYValue()).append(StringUtil.NEW_LINE);
            chartViewModel.onRolloverChanged("Series 1", seriesInfo.getFormattedXValue().toString(), seriesInfo.getFormattedYValue().toString());

            if (seriesInfo.seriesName != null) {
                final int start = sb.length();

                sb.append(seriesInfo.seriesName);
                sb.setSpan(new ForegroundColorSpan(ColorUtil.White), start, sb.length(), Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
                sb.append(StringUtil.NEW_LINE);
            }
            sb.append(modifierName);
            setText(sb);

            setSeriesColor(0xff6495ed);
        }
    }
}

Use the custom series info provider class in your code as shown below

Kotlin
Java

val lineSeries = FastLineRenderableSeries().apply {
    dataSeries = dataS
    strokeStyle = SolidPenStyle(0xffFF0010.toInt(), true, 3f, null)

    // Set custom series info provider
    seriesInfoProvider = CustomSeriesInfoProvider(chartViewModel)
}

surface.renderableSeries.add(lineSeries)
surface.chartModifiers.add(rolloverModifier)


// Use the custom series info provider class in your code as shown below
FastLineRenderableSeries lineSeries = new FastLineRenderableSeries();
lineSeries.setDataSeries(dataSeries);
lineSeries.setStrokeStyle(new SolidPenStyle(0xffFF0010, true, 3, null));

// Set custom series info provider
lineSeries.setSeriesInfoProvider(new CustomSeriesInfoProvider(chartViewModel));

Collections.addAll(surface.getRenderableSeries(), lineSeries);
Collections.addAll(surface.getChartModifiers(), rolloverModifier);

How It Works: Key Concepts Explained

1. SeriesInfo Extraction Process

The solution works by intercepting the tooltip creation and update process:

Custom SeriesInfoProvider: Extends DefaultXySeriesInfoProvider to provide custom tooltip
Custom Tooltip: Extends XySeriesTooltip and overrides internalUpdate(XySeriesInfo seriesInfo)
Data Extraction: In internalUpdate(), extract data from seriesInfo parameter
ViewModel Communication: Call chartViewModel.onRolloverChanged() with extracted data

2. SeriesInfo Data Available

The XySeriesInfo object provides access to:

seriesInfo.getFormattedXValue() - Formatted X value as shown in tooltip
seriesInfo.getFormattedYValue() - Formatted Y value as shown in tooltip
seriesInfo.getXValue() - Raw X value
seriesInfo.getYValue() - Raw Y value
seriesInfo.seriesName - Series name if set

3. Event Flow

User hovers over chart
    ↓
RolloverModifier detects hover
    ↓
CustomSeriesInfoProvider.getSeriesTooltipInternal() called
    ↓
CustomXySeriesTooltip.internalUpdate() called
    ↓
SeriesInfo extracted and passed to ViewModel
    ↓
ViewModel updates LiveData

Key Implementation Points

ViewModel Integration

ChartViewModel uses MutableLiveData<String> to hold rollover information
onRolloverChanged() method receives formatted SeriesInfo data
Exposes data through LiveData for UI components to observe

Custom SeriesInfoProvider

Extends DefaultXySeriesInfoProvider
Overrides getSeriesTooltipInternal() to return custom tooltip
Passes ChartViewModel reference to custom tooltip

Extends XySeriesTooltip
Overrides internalUpdate() method where SeriesInfo is available
Calls chartViewModel.onRolloverChanged() to pass data to ViewModel