List<List<ModelGroup>> ggParameters = new List<List<ModelGroup>>();

public RelayCommand<int> AddTestCommand { get; }

public MainViewModel()
{
    AddTestCommand = new RelayCommand<int>(AddTest);
    ggParameters.Add(new List<ModelGroup>
    {
        
        new ModelGroup("group1", new List<Model>
        {
            new Model(),
            new Model(),
            new Model(),
        }),
        new ModelGroup("group2", new List<Model>
        {
            new Model(),
            new Model(),
            new Model(),
        }),
    });
    B.Add(new GroupButton("Class1", 0, new RelayCommand<int>(ChangeShowedClass)));

    ggParameters.Add(new List<ModelGroup>
    {
        new ModelGroup("group3", new List<Model>
        {
            new Model(),
            new Model(),
            new Model(),
        }),
        new ModelGroup("group4", new List<Model>
        {
            new Model(),
            new Model(),
            new Model(),
        }),
    });
    B.Add(new GroupButton("Class2", 1, new RelayCommand<int>(ChangeShowedClass)));

    foreach (ModelGroup group in ggParameters[0])
    {
        A.Add(group);
    }

    C.Add("111");
}

private ObservableCollection<ModelGroup> _A = new ObservableCollection<ModelGroup>();
public ObservableCollection<ModelGroup> A
{
    get => _A;
    set
    {
        _A = value;
        OnPropertyChanged();
    }
}

private ObservableCollection<GroupButton> _B = new ObservableCollection<GroupButton>();
public ObservableCollection<GroupButton> B
{
    get => _B;
    set
    {
        _B = value;
        OnPropertyChanged();
    }
}

private ObservableCollection<string> _C = new ObservableCollection<string>();
public ObservableCollection<string> C
{
    get => _C;
    set
    {
        _C = value;
        OnPropertyChanged();
    }
}

private int _TestInt = 0;
public int TestInt
{
    get => _TestInt;
    set
    {
        _TestInt = value;
        OnPropertyChanged();
    }
}

private void ChangeShowedClass(int index)
{
    A.Clear();

    foreach (ModelGroup group in ggParameters[index])
    {
        A.Add(group);
    }
}

private void AddTest(int index)
{
    if (index == 0) 
    {
        C.Add("1111");
    }
    else
    {
        C.Add("2222");
    }
}

public class Model
{
    public string Name { get; set; }

    public Model()
    {
        Name = "-";
    }
}

public class ModelGroup : List<Model>
{
    public string GroupName { get; set; }

    public ModelGroup(string groupName, List<Model> models) : base(models)
    {
        GroupName = groupName;
    }
}

public class GroupButton : ObservableObject
{
    public string ButtonName { get; set; }
    public int ButtonNum { get; set; }

    public RelayCommand<int> ButtonCommand { get; set; }

    public GroupButton(string button_name, int button_num, RelayCommand<int> button_command)
    {
        ButtonName = button_name;
        ButtonNum = button_num;
        ButtonCommand = button_command;
    }
}

<StackLayout Grid.Column="0" BindableLayout.ItemsSource="{Binding B}">
    <BindableLayout.ItemTemplate>
        <DataTemplate>
            <Button Text="{Binding ButtonName}" Command="{Binding ButtonCommand}" CommandParameter="{Binding ButtonNum}"/>
        </DataTemplate>
    </BindableLayout.ItemTemplate>
</StackLayout>

<CollectionView Grid.Row="1" ItemsSource="{Binding A}" IsGrouped="True" ItemSizingStrategy="MeasureFirstItem">
    <CollectionView.ItemsLayout>
        <LinearItemsLayout Orientation="Vertical" ItemSpacing="1"/>
    </CollectionView.ItemsLayout>
    <CollectionView.GroupHeaderTemplate>
        <DataTemplate>
            <Label Text="{Binding GroupName}" FontAttributes="Bold" HeightRequest="30" VerticalTextAlignment="Center"/>
        </DataTemplate>
    </CollectionView.GroupHeaderTemplate>
    <CollectionView.ItemTemplate>
        <DataTemplate>
            <Border Padding="4" HeightRequest="45">
                <Grid RowSpacing="3" RowDefinitions="auto, auto">
                    <Grid ColumnDefinitions="*, 200, *">
                        <Label Text="{Binding Name}" VerticalTextAlignment="Center"/>
                    </Grid>
                </Grid>
            </Border>
        </DataTemplate>
    </CollectionView.ItemTemplate>
    <CollectionView.Footer>
        <Label Text="-  The End  -" HorizontalTextAlignment="Center"/>
    </CollectionView.Footer>
</CollectionView>

<CollectionView Grid.Row="1" ItemsSource="{Binding C}" ItemSizingStrategy="MeasureFirstItem">
</CollectionView>
<Entry Text="{Binding TestInt}"/>
<Button Text="AddTest" Command="{Binding AddTestCommand}" CommandParameter="{Binding TestInt}"/>