The IDelegateCommand and IAsyncCommand interfaces have been moved to the DevExpress.Mvvm namespace

What Changed

In v20.1 and earlier versions, the IDelegateCommand and IAsyncCommand interfaces were in a namespace for internal use - DevExpress.Mvvm.Native.
In v20.2, we have moved these interfaces to the public DevExpress.Mvvm namespace.
Currently the declaration is as follows:

C#
namespace DevExpress.Mvvm {
    public interface IDelegateCommand : ICommand {
        void RaiseCanExecuteChanged();
    }
    public interface IAsyncCommand : IDelegateCommand {
        bool IsExecuting { get; }
        CancellationTokenSource CancellationTokenSource { get; }
        bool IsCancellationRequested { get; }
        ICommand CancelCommand { get; }
        Task ExecuteAsync(object parameter);

        //Legacy and hidden API
        [EditorBrowsable(EditorBrowsableState.Never)]
        bool ShouldCancel { get; }
        //Legacy and hidden API
        [EditorBrowsable(EditorBrowsableState.Never)]
        void Wait(TimeSpan timeout);
    }
}

Visual Basic
Namespace DevExpress.Mvvm
    Interface IDelegateCommand
        Inherits ICommand

        Sub RaiseCanExecuteChanged()
    End Interface

    Interface IAsyncCommand
        Inherits IDelegateCommand

        ReadOnly Property IsExecuting As Boolean
        ReadOnly Property CancellationTokenSource As CancellationTokenSource
        ReadOnly Property IsCancellationRequested As Boolean
        ReadOnly Property CancelCommand As ICommand
        Function ExecuteAsync(ByVal parameter As Object) As Task

        '''Legacy And hidden API
        <EditorBrowsable(EditorBrowsableState.Never)>
        ReadOnly Property ShouldCancel As Boolean
        '''Legacy And hidden API
        <EditorBrowsable(EditorBrowsableState.Never)>
        Sub Wait(ByVal timeout As TimeSpan)
    End Interface
End Namespace

Reasons for Change

We have public functions that return an IDelegateCommand or IAsyncCommand object. In previous versions, public APIs returned objects declared in a namespace for internal use (DevExpress.Mvvm.Native):

C#
namespace DevExpress.Mvvm.POCO {
    public static class POCOViewModelExtensions {
        ...
        public static IDelegateCommand GetCommand<T>(this T viewModel, Expression<Action<T>> methodExpression) { ... }
        public static IAsyncCommand GetAsyncCommand<T>(this T viewModel, Expression<Func<T, Task>> methodExpression) { ... }
    }
}

Visual Basic
Namespace DevExpress.Mvvm.POCO
    Module POCOViewModelExtensions
        ...
        <Extension()>
        Function GetCommand(Of T)(ByVal viewModel As T, ByVal methodExpression As Expression(Of Action(Of T))) As IDelegateCommand
            ...
        End Function
        <Extension()>
        Function GetAsyncCommand(Of T)(ByVal viewModel As T, ByVal methodExpression As Expression(Of Func(Of T, Task))) As IAsyncCommand
            ...
        End Function
    End Module
End Namespace

These functions are used in POCO ViewModels. In addition to these methods, we implemented similar functions in ViewModelBase in v20.2:

C#
namespace DevExpress.Mvvm {
    public abstract class ViewModelBase : BindableBase {
        ...
        protected IDelegateCommand GetCommand(Expression<Action> commandMethodExpression) { ... }
        protected IAsyncCommand GetAsyncCommand(Expression<Func<Task>> commandMethodExpression) { ... }
    }
}

Visual Basic
Namespace DevExpress.Mvvm
    Public MustInherit Class ViewModelBase
        Inherits BindableBase
        ...
        Protected Function GetCommand(ByVal commandMethodExpression As Expression(Of Action)) As IDelegateCommand
            ...
        End Function
        Protected Function GetAsyncCommand(ByVal commandMethodExpression As Expression(Of Func(Of Task))) As IAsyncCommand
            ...
        End Function
    End Class
End Namespace

How to Update Existing Apps

If you encounter a compilation error - "IDelegateCommand or IAsyncCommand could not be found", check that you referenced the DevExpress.Mvvm namespace in the files where this error occurs:

C#
using DevExpress.Mvvm;

Visual Basic
Imports DevExpress.Mvvm