PresentationBase 3.4.0-preview

Take a look at the Quick start in the wiki. Here are some basic examples:

ViewModels with bindable properties

// C# code
public class AwesomeViewModel : ViewModel
{
    private string _name;
  
    public string Name
    {
        get => _name;
        set => SetProperty(ref _name, value);
    }
}

<!-- XAML -->
<TextBox Text="{Binding Name, UpdateSourceTrigger=PropertyChanged}" />

... and with property validation

// C# code
public class AwesomeViewModel : ViewModel
{
    private string _name;

    public string Name
    {
        get => _name;
        set => SetProperty(ref _name, value, NameValidation);
    }

    private IEnumerable<string> NameValidation(string value)
    {
        if (string.IsNullOrEmpty(value))
            yield return "Name cannot be null or empty!";
        else if (value == "sungaila")
            yield return "Name cannot be stupid!";
    }
}

<!-- XAML -->
<TextBox Text="{Binding Name, UpdateSourceTrigger=PropertyChanged}" />

ViewModel collections

// C# code
public class AwesomeViewModel : ViewModel
{
    public ObservableViewModelCollection<ChildViewModel> Children { get; }
    
    public AwesomeViewModel()
    {
        Children = new ObservableViewModelCollection<ChildViewModel>(this);
        Children.Add(new ChildViewModel { Nickname = "Blinky" });
        Children.Add(new ChildViewModel { Nickname = "Pinky" });
        Children.Add(new ChildViewModel { Nickname = "Inky" });
        Children.Add(new ChildViewModel { Nickname = "Clyde" });
    }
}

<!-- XAML -->
<ListView ItemsSource="{Binding Children}">
    <ListView.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding Nickname}" />
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

... and collection compositions

// C# code
public class AwesomeViewModel : ViewModel
{
    public ObservableViewModelCollection<ChildViewModel> Children { get; }

    public ObservableViewModelCollection<PersonViewModel> People { get; }

    public CompositeViewModelCollection<ViewModel> Composition { get; }
    
    public AwesomeViewModel()
    {
        Children = new ObservableViewModelCollection<ChildViewModel>(this);
        Children.Add(new ChildViewModel { Nickname = "Blinky" });
        Children.Add(new ChildViewModel { Nickname = "Pinky" });
        Children.Add(new ChildViewModel { Nickname = "Inky" });
        Children.Add(new ChildViewModel { Nickname = "Clyde" });

        People = new ObservableViewModelCollection<PersonViewModel>(this);
        People.Add(new PersonViewModel { Nickname = "Kevin" });
        People.Add(new PersonViewModel { Nickname = "Tommy" });

        Composition = new CompositeViewModelCollection<ViewModel>();
        Composition.Add(Children);
        Composition.Add(People);
    }
}

<!-- XAML -->
<ListView ItemsSource="{Binding Composition}">
    <ListView.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding Nickname}" />
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

Commands

Your command can be defined anywhere you want (as long as its assembly is referenced by the WPF application). Please note that a parameterless constructor (or none at all) is needed.

// C# code
public class AlertCommand : ViewModelCommand<AwesomeViewModel>
{
    public override void Execute(AwesomeViewModel parameter)
    {
        System.Windows.MessageBox.Show("You just clicked that button.");
    }

    public override bool CanExecute(AwesomeViewModel parameter)
    {
        return parameter.Name != "John Doe";
    }
}

The only reference needed is the x:Type in XAML. Important: Make sure to write CommandParameter before Command to avoid problems with CanExecute. Consider to create an issue for the .NET Core team (like this one) if you want this WPF bug fixed.

<!-- XAML -->
<Window x:Class="WpfApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:Core="clr-namespace:PresentationBase;assembly=PresentationBase"
        xmlns:local="clr-namespace:WpfApp">
        
        <Button CommandParameter="{Binding}"
                Command="{Core:CommandBinding {x:Type local:AlertCommand}}" />
</Window>

... and async commands

// C# code
public class AlertCommandAsync : ViewModelCommandAsync<AwesomeViewModel>
{
    protected override async Task ExecutionAsync(AwesomeViewModel parameter)
    {
        await Task.Run(() =>
        {
            System.Threading.Thread.Sleep(2000);
            System.Windows.MessageBox.Show("You clicked that button two seconds ago.");
        });
    }
}

<!-- XAML -->
<Window x:Class="WpfApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:Core="clr-namespace:PresentationBase;assembly=PresentationBase"
        xmlns:local="clr-namespace:WpfApp">
        
        <Button CommandParameter="{Binding}"
                Command="{Core:CommandBinding {x:Type local:AlertCommandAsync}}" />
</Window>

ValueConverters

<!-- XAML -->
<Window x:Class="WpfApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:Converters="clr-namespace:PresentationBase.Converters;assembly=PresentationBase"
        xmlns:local="clr-namespace:WpfApp">
        
        <TextBox Visibility="{Binding Name, Converter={Converters:NullToVisibilityConverter}}" />
</Window>