Automatic Updates

View model

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using LiveChartsCore;
using LiveChartsCore.Defaults;
using LiveChartsCore.SkiaSharpView;

namespace ViewModelsSamples.Lines.AutoUpdate;

public partial class ViewModel : ObservableObject
{
    private readonly Random _random = new();
    private readonly ObservableCollection<ObservableValue> _observableValues;

    public ViewModel()
    {
        // Use ObservableCollections to let the chart listen for changes (or any INotifyCollectionChanged). // mark
        _observableValues = new ObservableCollection<ObservableValue>
        {
            // Use the ObservableValue or ObservablePoint types to let the chart listen for property changes // mark
            // or use any INotifyPropertyChanged implementation // mark
            new ObservableValue(2),
            new(5), // the ObservableValue type is redundant and inferred by the compiler (C# 9 and above)
            new(4),
            new(5),
            new(2),
            new(6),
            new(6),
            new(6),
            new(4),
            new(2),
            new(3),
            new(4),
            new(3)
        };

        Series = new ObservableCollection<ISeries>
        {
            new LineSeries<ObservableValue>
            {
                Values = _observableValues,
                Fill = null
            }
        };

        // in the following sample notice that the type int does not implement INotifyPropertyChanged
        // and our Series.Values property is of type List<T>
        // List<T> does not implement INotifyCollectionChanged
        // this means the following series is not listening for changes.
        // Series.Add(new ColumnSeries<int> { Values = new List<int> { 2, 4, 6, 1, 7, -2 } }); // mark
    }

    public ObservableCollection<ISeries> Series { get; set; }

    [RelayCommand]
    public void AddItem()
    {
        var randomValue = _random.Next(1, 10);
        _observableValues.Add(new(randomValue));
    }

    [RelayCommand]
    public void RemoveItem()
    {
        if (_observableValues.Count == 0) return;
        _observableValues.RemoveAt(0);
    }

    [RelayCommand]
    public void UpdateItem()
    {
        var randomValue = _random.Next(1, 10);

        // we grab the last instance in our collection
        var lastInstance = _observableValues[_observableValues.Count - 1];

        // finally modify the value property and the chart is updated!
        lastInstance.Value = randomValue;
    }

    [RelayCommand]
    public void ReplaceItem()
    {
        var randomValue = _random.Next(1, 10);
        var randomIndex = _random.Next(0, _observableValues.Count - 1);
        _observableValues[randomIndex] = new(randomValue);
    }

    [RelayCommand]
    public void AddSeries()
    {
        //  for this sample only 5 series are supported.
        if (Series.Count == 5) return;

        Series.Add(
            new LineSeries<int>
            {
                Values = new List<int>
                {
                    _random.Next(0, 10),
                    _random.Next(0, 10),
                    _random.Next(0, 10)
                }
            });
    }

    [RelayCommand]
    public void RemoveSeries()
    {
        if (Series.Count == 1) return;

        Series.RemoveAt(Series.Count - 1);
    }
}

XAML

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="XamarinSample.Lines.AutoUpdate.View"
             xmlns:lvc="clr-namespace:LiveChartsCore.SkiaSharpView.Xamarin.Forms;assembly=LiveChartsCore.SkiaSharpView.XamarinForms"
             xmlns:vms="clr-namespace:ViewModelsSamples.Lines.AutoUpdate;assembly=ViewModelsSamples">
    <ContentPage.BindingContext>
        <vms:ViewModel/>
    </ContentPage.BindingContext>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="50"/>
            <RowDefinition Height="50"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <StackLayout Grid.Row="0" Orientation="Horizontal">
            <Button Margin="6" Command="{Binding AddItemCommand}" Text="Add item" />
            <Button Margin="6" Command="{Binding ReplaceItemCommand}" Text="Replace item"/>
            <Button Margin="6" Command="{Binding RemoveItemCommand}" Text="Remove item"/>
        </StackLayout>
        <StackLayout Grid.Row="1" Orientation="Horizontal">
            <Button Margin="6" Command="{Binding AddSeriesCommand}" Text="Add Series"/>
            <Button Margin="6" Command="{Binding RemoveSeriesCommand}" Text="Remove Series" />
            <Button Margin="6" Clicked="Button_Clicked" Text="Constant changes" />
        </StackLayout>
        <lvc:CartesianChart Grid.Row="2" Series="{Binding Series}"></lvc:CartesianChart>
    </Grid>
</ContentPage>

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