community/InkCanvasForClass.IccInkCanvas/Utils/Threading/VisualTargetPresentationSource.cs

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Media;

namespace InkCanvasForClass.IccInkCanvas.Utils.Threading
{
    /// <summary>
    ///     The VisualTargetPresentationSource represents the root
    ///     of a visual subtree owned by a different thread that the
    ///     visual tree in which is is displayed.
    /// </summary>
    /// <remarks>
    ///     A HostVisual belongs to the same UI thread that owns the
    ///     visual tree in which it resides.
    ///     
    ///     A HostVisual can reference a VisualTarget owned by another
    ///     thread.
    ///     
    ///     A VisualTarget has a root visual.
    ///     
    ///     VisualTargetPresentationSource wraps the VisualTarget and
    ///     enables basic functionality like Loaded, which depends on
    ///     a PresentationSource being available.
    /// </remarks>
    public class VisualTargetPresentationSource : PresentationSource, IDisposable
    {
        public VisualTargetPresentationSource(HostVisual hostVisual)
        {
            _visualTarget = new VisualTarget(hostVisual);
        }

        public override Visual RootVisual
        {
            get => _visualTarget.RootVisual;
            set
            {
                if (IsDisposed)
                {
                    throw new ObjectDisposedException("VisualTarget");
                }

                var oldRoot = _visualTarget.RootVisual;

                // Set the root visual of the VisualTarget.  This visual will
                // now be used to visually compose the scene.
                _visualTarget.RootVisual = value;

                // Hook the SizeChanged event on framework elements for all
                // future changed to the layout size of our root, and manually
                // trigger a size change.
                if (oldRoot is FrameworkElement oldRootFe)
                {
                    oldRootFe.SizeChanged -= root_SizeChanged;
                }
                if (value is FrameworkElement rootFe)
                {
                    rootFe.SizeChanged += root_SizeChanged;
                    rootFe.DataContext = _dataContext;

                    if (_propertyName != null)
                    {
                        var myBinding = new Binding(_propertyName)
                        {
                            Source = _dataContext
                        };
                        rootFe.SetBinding(TextBlock.TextProperty, myBinding);
                    }
                }

                // Tell the PresentationSource that the root visual has
                // changed.  This kicks off a bunch of stuff like the
                // Loaded event.
                RootChanged(oldRoot, value);

                // Kickoff layout...
                if (value is UIElement rootElement)
                {
                    rootElement.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
                    rootElement.Arrange(new Rect(rootElement.DesiredSize));
                }
            }
        }

        public object DataContext
        {
            get => _dataContext;
            set
            {
                if (IsDisposed)
                {
                    throw new ObjectDisposedException("VisualTarget");
                }

                if (_dataContext == value)
                {
                    return;
                }

                _dataContext = value;
                if (_visualTarget.RootVisual is FrameworkElement rootElement)
                {
                    rootElement.DataContext = _dataContext;
                }
            }
        }

        public string PropertyName
        {
            get => _propertyName;
            set
            {
                if (IsDisposed)
                {
                    throw new ObjectDisposedException("VisualTarget");
                }

                _propertyName = value;

                if (_visualTarget.RootVisual is TextBlock rootElement)
                {
                    if (!rootElement.CheckAccess())
                    {
                        throw new InvalidOperationException("What?");
                    }

                    var myBinding = new Binding(_propertyName)
                    {
                        Source = _dataContext
                    };
                    rootElement.SetBinding(TextBlock.TextProperty, myBinding);
                }
            }
        }

        public event SizeChangedEventHandler SizeChanged;

        public override bool IsDisposed => _isDisposed;

        protected override CompositionTarget GetCompositionTargetCore()
        {
            return _visualTarget;
        }

        private void root_SizeChanged(object sender, SizeChangedEventArgs e)
        {
            if (IsDisposed)
            {
                return;
            }

            SizeChanged?.Invoke(this, e);
        }

        private readonly VisualTarget _visualTarget;
        private object _dataContext;
        private string _propertyName;
        private bool _isDisposed;

        public void Dispose()
        {
            _visualTarget?.Dispose();
            _isDisposed = true;
        }
    }
}