我正在开发 WPF 中的一个项目，该项目每秒最多更新 30 次视图。据我所知，我正在使用 MVVM 模式，并且对目前的结果非常满意。但是我想知道是否没有更有效的方法来更新我的宿主容器的 VisualCollection 中的 DrawingVisuals。在我的视图模型中的每个属性更改时，我都会发现，删除然后为该视图模型重新添加一个新的 DrawingVisual。对于不断移动的对象，我觉得应该有更好的方法，例如将 DrawingVisuals 本身直接绑定到视图模型的属性，但那会是什么样子呢？随着模拟中模型数量的增加，我需要确保我有一个简化的更新工作流程。我开始遵循这里的示例：http: //msdn.microsoft.com/en-us/library/ms742254。
我故意避免 DependencyProperties 并将 UserControls 绑定到每个视图模型，因为我需要一个非常有效的绘图画布（因此下面的 QuickCanvas）。因此，除了设计主 UI 和连接按钮和命令外，我几乎不需要 XAML。请询问是否有一些不清楚的地方，或者我遗漏了一些重要的东西。谢谢！
可视主机容器（视图）：
public partial class QuickCanvas : FrameworkElement
{
private readonly VisualCollection _visuals;
private readonly Dictionary<Guid, DrawingVisual> _visualDictionary;
public static readonly DependencyProperty ItemsSourceProperty =
DependencyProperty.Register("ItemsSource", typeof(ObservableNotifiableCollection<IVisualModel>),
typeof(QuickCanvas),
new PropertyMetadata(OnItemsSourceChanged));
public QuickCanvas()
{
InitializeComponent();
_visuals = new VisualCollection(this);
_visualDictionary = new Dictionary<Guid, DrawingVisual>();
}
public ObservableNotifiableCollection<IVisualModel> ItemsSource
{
set { SetValue(ItemsSourceProperty, value); }
get { return (ObservableNotifiableCollection<IVisualModel>)GetValue(ItemsSourceProperty); }
}
protected override void OnPropertyChanged(DependencyPropertyChangedEventArgs e)
{
base.OnPropertyChanged(e);
if (e.Property.Name == "Width" || e.Property.Name == "Height" || e.Property.Name == "Center")
{
UpdateVisualChildren();
}
}
private void UpdateVisualChildren()
{
if (ItemsSource == null || _visuals.Count == 0) return;
foreach (var model in ItemsSource)
{
var visual = FindVisualForModel(model);
if (visual != null)
{
UpdateVisualFromModel(visual, model);
}
}
}
private void UpdateVisualPairFromModel(DrawingVisual visual, IVisualModel model)
{
visual.Transform = ApplyVisualTransform(visual.Transform, model);
}
private static void OnItemsSourceChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
(obj as QuickCanvas).OnItemsSourceChanged(args);
}
private void OnItemsSourceChanged(DependencyPropertyChangedEventArgs args)
{
_visuals.Clear();
if (args.OldValue != null)
{
var models = args.OldValue as ObservableNotifiableCollection<IVisualModel>;
models.CollectionCleared -= OnCollectionCleared;
models.CollectionChanged -= OnCollectionChanged;
models.ItemPropertyChanged -= OnItemPropertyChanged;
}
if (args.NewValue != null)
{
var models = args.NewValue as ObservableNotifiableCollection<IVisualModel>;
models.CollectionCleared += OnCollectionCleared;
models.CollectionChanged += OnCollectionChanged;
models.ItemPropertyChanged += OnItemPropertyChanged;
CreateVisualChildren(models);
}
}
private void OnCollectionCleared(object sender, EventArgs args)
{
_visuals.Clear();
_visualDictionary.Clear();
}
private void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs args)
{
if (args.OldItems != null)
RemoveVisualChildren(args.OldItems);
if (args.NewItems != null)
CreateVisualChildren(args.NewItems);
}
private void OnItemPropertyChanged(object sender, ItemPropertyChangedEventArgs args)
{
var model = args.Item as IVisualModel;
if (model == null)
throw new ArgumentException("args.Item was expected to be of type IVisualModel but was not.");
//TODO is there a better way to update without having to add/remove visuals?
var visual = FindVisualForModel(model);
_visuals.Remove(visual);
visual = CreateVisualFromModel(model);
_visuals.Add(visual);
_visualDictionary[model.Id] = visual;**
}
private DrawingVisual FindVisualForModel(IVisualModel model)
{
return _visualDictionary[model.Id];
}
private void CreateVisualChildren(IEnumerable models)
{
foreach (IVisualModel model in models)
{
var visual = CreateVisualFromModel(model);
_visuals.Add(visual);
_visuals.Add(visual);
_visualDictionary.Add(model.Id, visual);
}
}
private DrawingVisual CreateVisualFromModel(IVisualModel model)
{
var visual = model.GetVisual();
UpdateVisualFromModel(visual, model);
return visual;
}
private void RemoveVisualChildren(IEnumerable models)
{
foreach (IVisualModel model in models)
{
var visual = FindVisualForModel(model);
if (visual != null)
{
_visuals.Remove(visual);
_visualDictionary.Remove(model.Id);
}
}
}
protected override int VisualChildrenCount
{
get
{
return _visuals.Count;
}
}
protected override Visual GetVisualChild(int index)
{
if (index < 0 || index >= _visuals.Count)
throw new ArgumentOutOfRangeException("index");
return _visuals[index];
}
}
一个 IVisuaModel 实现：
public class VehicleViewModel : IVisualModel
{
private readonly Vehicle _vehicle;
private readonly IVisualFactory<VehicleViewmodel> _visualFactory;
private readonly IMessageBus _messageBus;
public VehicleViewmodel(Vehicle vehicle, IVisualFactory<VehicleViewmodel> visualFactory, IMessageBus messageBus)
{
_vehicle = vehicle;
_visualFactory = visualFactory;
_messageBus = messageBus;
_messageBus.Subscribe<VehicleMovedMessage>(VehicleMoveHandler, Dispatcher.CurrentDispatcher);
Id = Guid.NewGuid();
}
public void Dispose()
{
_messageBus.Unsubscribe<VehicleMovedMessage>(VehicleMoveHandler);
}
private void VehicleMoveHandler(VehicleMovedMessage message)
{
if (message.Vehicle.Equals(_vehicle))
OnPropertyChanged("");
}
public Guid Id { get; private set; }
public Point Anchor { get { return _vehicle.Position; } }
public double Rotation { get { return _vehicle.Orientation; } }
public DrawingVisual GetVisual()
{
return _visualFactory.Create(this);
}
public double Width { get { return _vehicle.VehicleType.Width; } }
public double Length { get { return _vehicle.VehicleType.Length; } }
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
var handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}
一个 IVisualFactory 实现：
public class VehicleVisualFactory : IVisualFactory<VehicleViewModel>
{
private readonly IDictionary<string, Pen> _pens;
private readonly IDictionary<string, Brush> _brushes;
public VehicleVisualFactory(IDictionary<string, Pen> pens, IDictionary<string, Brush> brushes)
{
_pens = pens;
_brushes = brushes;
}
public DrawingVisual Create(VehicleViewmodel viewModel)
{
var result = new DrawingVisual();
using (var context = result.RenderOpen())
{
context.DrawRectangle(_brushes["VehicleGreen"], _pens["VehicleDarkGreen"],
new Rect(-viewModel.Width / 2, -viewModel.Length / 2, viewModel.Width, viewModel.Length));
}
return result;
}
}