Conditional Draw

Razor

@page "/General/ConditionalDraw"
@using LiveChartsCore.SkiaSharpView.Blazor
@using LiveChartsCore;
@using LiveChartsCore.Defaults;
@using LiveChartsCore.Kernel;
@using LiveChartsCore.SkiaSharpView;
@using LiveChartsCore.SkiaSharpView.Painting;
@using LiveChartsCore.VisualStates;
@using SkiaSharp;
@using LiveChartsCore.Drawing;
@using System.Collections.ObjectModel

<CartesianChart
    Series="@series"
    TooltipPosition="LiveChartsCore.Measure.TooltipPosition.Bottom">
</CartesianChart>

@code {
    private ObservableCollection<ObservableValue> _values = new ObservableCollection<ObservableValue>
    {
        new ObservableValue(2),
        new ObservableValue(3),
        new ObservableValue(4)
    };
    private Random _random = new Random();
    private ISeries[] series;

    protected override void OnInitialized()
    {
        var columnSeries = new ColumnSeries<ObservableValue>
        {
            ShowDataLabels = true,
            DataLabelsSize = 15,
            Values = _values
        };
        columnSeries.PointMeasured += OnPointMeasured;

        columnSeries.HasState("Danger", [
            (nameof(IDrawnElement.Fill), new SolidColorPaint(SKColors.Red))
        ]);

        columnSeries.HasState("LabelDanger", [
            (nameof(IDrawnElement.Paint), new SolidColorPaint(SKColors.Red)),
            (nameof(BaseLabelGeometry.TextSize), 30f)
        ]);

        columnSeries.HasState("Hover", [
            (nameof(IDrawnElement.DropShadow), new LvcDropShadow(4, 4, 16, 16, new(0, 0, 255)))
        ]);

        series = new ISeries[] { columnSeries };

        _ = Randomize();
    }

    private void OnPointMeasured(ChartPoint point)
    {
        var ctx = point.Context;
        if (ctx.DataSource is not ObservableValue observable) return;

        var states = ctx.Series.VisualStates;

        if (observable.Value > 5)
        {
            states.SetState("Danger", ctx.Visual);
            states.SetState("LabelDanger", ctx.Label);
        }
        else
        {
            states.ClearState("Danger", ctx.Visual);
            states.ClearState("LabelDanger", ctx.Label);
        }
    }

    private async Task Randomize()
    {
        while (true)
        {
            await Task.Delay(3000);
            foreach (var item in _values)
            {
                item.Value = _random.Next(1, 10);
            }
        }
    }
}

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