DEV EXPRESS CHARTS IN .NET MAUI
In this instance, the chart features line series displaying the annual GDP
for three countries. Generate a ViewModel.cs file that includes the
following classes:

public class ViewModel 
    public CountryGdp GdpValueForUSA  get; 
    public CountryGdp GdpValueForChina  get; 
    public CountryGdp GdpValueForJapan  get; 

    public ViewModel() 
        GdpValueForUSA = new CountryGdp(
            "USA",
            new GdpValue(new DateTime(2020, 1, 1), 20.93),
            new GdpValue(new DateTime(2019, 1, 1), 21.43),
            new GdpValue(new DateTime(2018, 1, 1), 20.58),
            new GdpValue(new DateTime(2017, 1, 1), 19.391),
            new GdpValue(new DateTime(2016, 1, 1), 18.624),
            new GdpValue(new DateTime(2015, 1, 1), 18.121),
            new GdpValue(new DateTime(2014, 1, 1), 17.428),
            new GdpValue(new DateTime(2013, 1, 1), 16.692),
            new GdpValue(new DateTime(2012, 1, 1), 16.155),
            new GdpValue(new DateTime(2011, 1, 1), 15.518),
            new GdpValue(new DateTime(2010, 1, 1), 14.964)
        );
        GdpValueForChina = new CountryGdp(
            "China",
            new GdpValue(new DateTime(2020, 1, 1), 14.72),
            new GdpValue(new DateTime(2019, 1, 1), 14.34),
            new GdpValue(new DateTime(2018, 1, 1), 13.89),
            new GdpValue(new DateTime(2017, 1, 1), 12.238),
            new GdpValue(new DateTime(2016, 1, 1), 11.191),
            new GdpValue(new DateTime(2015, 1, 1), 11.065),
            new GdpValue(new DateTime(2014, 1, 1), 10.482),
            new GdpValue(new DateTime(2013, 1, 1), 9.607),
            new GdpValue(new DateTime(2012, 1, 1), 8.561),
            new GdpValue(new DateTime(2011, 1, 1), 7.573),
            new GdpValue(new DateTime(2010, 1, 1), 6.101)
        );
        GdpValueForJapan = new CountryGdp(
            "Japan",
            new GdpValue(new DateTime(2020, 1, 1), 4.888),
            new GdpValue(new DateTime(2019, 1, 1), 5.082),
            new GdpValue(new DateTime(2018, 1, 1), 4.955),
            new GdpValue(new DateTime(2017, 1, 1), 4.872),
            new GdpValue(new DateTime(2016, 1, 1), 4.949),
            new GdpValue(new DateTime(2015, 1, 1), 4.395),
            new GdpValue(new DateTime(2014, 1, 1), 4.850),
            new GdpValue(new DateTime(2013, 1, 1), 5.156),
            new GdpValue(new DateTime(2012, 1, 1), 6.203),
            new GdpValue(new DateTime(2011, 1, 1), 6.156),
            new GdpValue(new DateTime(2010, 1, 1), 5.700)
        );
    


public class CountryGdp 
    public string CountryName  get; 
    public IList<GdpValue> Values  get; 

    public CountryGdp(string country, params GdpValue[] values) 
        this.CountryName = country;
        this.Values = new List<GdpValue>(values);
    


public class GdpValue 
    public DateTime Year  get; 
    public double Value  get; 

    public GdpValue(DateTime year, double value) 
        this.Year = year;
        this.Value = value;
    

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