Following is the MainWindowViewModel.cs code :

using System;
using System.Collections.ObjectModel;
using System.Linq;
using CommunityToolkit.Mvvm.ComponentModel;
using Neuroflow.Views;
using Neuroflow.Views.VisualizationViews;
using Avalonia.Controls;
using CommunityToolkit.Mvvm.Input;
using Neuroflow.Services;

namespace Neuroflow.ViewModels;

public partial class MainWindowViewModel : ViewModelBase
{
    [ObservableProperty] private TabItem? _currentOpenedView;

    [ObservableProperty] private ObservableCollection<TabItem> _openedViews;

    public MainWindowViewModel()
    {
        OpenedViews = new ObservableCollection<TabItem>
        {
            new TabItem("Visualization", new Visualization()),
            new TabItem("Linear Regression", new LinearRegression()),
            new TabItem("Logistic Regression", new LogisticRegression())
        };
       
    }
}

public partial class TabItem : ViewModelBase
{
    [ObservableProperty] private string _header;
    [ObservableProperty] private UserControl _content;

    public TabItem(string title, UserControl view)
    {
        Header = title;
        Content = view ?? throw new ArgumentNullException(nameof(view));
    }
}

MainWindow.axaml :

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="using:Neuroflow.ViewModels"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:views="clr-namespace:Neuroflow.Views;assembly=Neuroflow"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        xmlns:local="using:Neuroflow.Views"
        x:Class="Neuroflow.Views.MainWindow"
        x:DataType="vm:MainWindowViewModel"
        Icon="/Assets/avalonia-logo.ico"
        Title="Neuroflow"
        WindowState="Maximized"
        RequestedThemeVariant="Light">

    <Window.DataContext>
        <vm:MainWindowViewModel />
    </Window.DataContext>

    <Design.DataContext>
        <vm:MainWindowViewModel />
    </Design.DataContext>


    

        <TabControl Name="InnerContent" ItemsSource="{Binding OpenedViews}" >

            <TabControl.ItemTemplate>
                <DataTemplate>
                    <ContentControl Content="{Binding Header}" FontSize="12" />
                </DataTemplate>
            </TabControl.ItemTemplate>

            <TabControl.ContentTemplate>
                <DataTemplate>
                    <ContentPresenter Content="{Binding   CurrentOpenedView.Content}" />
                </DataTemplate>
            </TabControl.ContentTemplate>

        </TabControl>

    </DockPanel>
</Window>

The code is properly rendering the Title, however doesn’t render the Content properly ( works fine when i hard code everything ), so the problem seems to be arising from the template code.I also tried the following ( doesn’t work either )

<TabControl x:Name="TabControl" ItemsSource="{Binding OpenedViews}"></TabControl>

Also tried the following :

<ContentControl Content="{Binding CurrentOpenedView.Content}" />

Replacing CurrentOpenedView.Content with Content doesn’t work ( Intellisence gives red lines before hand )

The error i get is :

0>MainWindow.axaml(68,37): Error AVLN2000 Avalonia: Unable to resolve property or method of name 'CurrentOpenedView' on type 'XamlX.TypeSystem.XamlPseudoType'. Line 68, position 37.

0>------- Finished building project: Neuroflow. Succeeded: False. Errors: 1. Warnings: 4