TabControl with Add New Tab Button (+)

Existing answers were too complex for me and I am lazy. So, I tried to implement a very simple idea.

1. Always add [+] tab to the last.
2. When the last tab is selected, make it as a new tab, and add another last tab.

The idea was simple, but the damn WPF is verbose, so the code became a little bit long. But it probably is very simple to understand... because even I did.

Code behind.

public partial class MainWindow : Window
{
    int TabIndex = 1;
    ObservableCollection<TabVM> Tabs = new ObservableCollection<TabVM>();
    public MainWindow()
    {
        InitializeComponent();
        var tab1 = new TabVM()
        {
            Header = $"Tab {TabIndex}",
            Content = new ContentVM("First tab", 1)
        };
        Tabs.Add(tab1);
        AddNewPlusButton();

        MyTabControl.ItemsSource = Tabs;
        MyTabControl.SelectionChanged += MyTabControl_SelectionChanged;

    }

    private void MyTabControl_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        if(e.Source is TabControl)
        {
            var pos = MyTabControl.SelectedIndex;
            if (pos!=0 && pos == Tabs.Count-1) //last tab
            {
                var tab = Tabs.Last();
                ConvertPlusToNewTab(tab);
                AddNewPlusButton();
            }
        }
    }

    void ConvertPlusToNewTab(TabVM tab)
    {
        //Do things to make it a new tab.
        TabIndex++;
        tab.Header = $"Tab {TabIndex}";
        tab.IsPlaceholder = false;
        tab.Content = new ContentVM("Tab content", TabIndex);
    }

    void AddNewPlusButton()
    {
        var plusTab = new TabVM()
        {
            Header = "+",
            IsPlaceholder = true
        };
        Tabs.Add(plusTab);
    }

    class TabVM:INotifyPropertyChanged
    {
        string _Header;
        public string Header
        {
            get => _Header;
            set
            {
                _Header = value;
                OnPropertyChanged();
            }
        }

        bool _IsPlaceholder = false;
        public bool IsPlaceholder
        {
            get => _IsPlaceholder;
            set
            {
                _IsPlaceholder = value;
                OnPropertyChanged();
            }
        }

        ContentVM _Content = null;
        public ContentVM Content
        {
            get => _Content;
            set
            {
                _Content = value;
                OnPropertyChanged();
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        void OnPropertyChanged([CallerMemberName] string property = "")
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(property));
        }
    }

    class ContentVM
    {
        public ContentVM(string name, int index)
        {
            Name = name;
            Index = index;
        }
        public string Name { get; set; }
        public int Index { get; set; }
    }

    private void OnTabCloseClick(object sender, RoutedEventArgs e)
    {
        var tab = (sender as Button).DataContext as TabVM;
        if (Tabs.Count>2)
        { 
            var index = Tabs.IndexOf(tab);
            if(index==Tabs.Count-2)//last tab before [+]
            {
                MyTabControl.SelectedIndex--;
            }
            Tabs.RemoveAt(index);
        }
    }
}

XAML

<TabControl Name="MyTabControl">
    <TabControl.ItemTemplate>
        <DataTemplate>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="{Binding Header, Mode=OneWay}" />
                <Button Click="OnTabCloseClick" Width="20" Padding="0" Margin="8 0 0 0" Content="X">
                    <Button.Style>
                        <Style TargetType="Button" x:Name="CloseButtonStyle">
                            <Setter Property="Visibility" Value="Visible"/>
                            <Style.Triggers>
                                <DataTrigger Binding="{Binding IsPlaceholder}" Value="True">
                                    <Setter Property="Visibility" Value="Collapsed"/>
                                </DataTrigger>
                            </Style.Triggers>
                        </Style>
                    </Button.Style>
                </Button>
            </StackPanel>
        </DataTemplate>
    </TabControl.ItemTemplate>

    <TabControl.ContentTemplate>
        <DataTemplate>
            <ContentControl>
                <ContentControl.Resources>
                    <ContentControl x:Key="TabContentTemplate">
                        <StackPanel DataContext="{Binding Content}" Orientation="Vertical">
                            <TextBlock Text="{Binding Path=Name}"/>
                            <TextBlock Text="{Binding Path=Index}"/>
                        </StackPanel>
                    </ContentControl>
                </ContentControl.Resources>
                <ContentControl.Style>
                    <Style TargetType="ContentControl">
                        <Style.Triggers>
                            <DataTrigger Binding="{Binding IsPlaceholder}" Value="True">
                                <Setter Property="Content"
                                        Value="{x:Null}"/>                                    
                            </DataTrigger>
                            <DataTrigger Binding="{Binding IsPlaceholder}" Value="False">
                                <Setter Property="Content"
                                        Value="{StaticResource TabContentTemplate}"/>
                            </DataTrigger>
                        </Style.Triggers>
                    </Style>
                </ContentControl.Style>
            </ContentControl>
        </DataTemplate>
    </TabControl.ContentTemplate>
</TabControl>

To complete the answer given by @NVM what you have to add is the PreviewMouseDown event:

<TabControl PreviewMouseDown="ActionTabs_PreviewMouseDown"
</TabControl>

And then:

private void ActionTabs_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
  ouseButtonEventArgs args = e as MouseButtonEventArgs;

  FrameworkElement source = (FrameworkElement)args.OriginalSource;

  if (source.DataContext.ToString() == "{NewItemPlaceholder}")
  {
      e.Handled = true;
  }
}