c# – 使用MVVM模式更新WPF中VisualCollection主机中的DrawingVi

我正在使用 WPF中的一个项目,每秒更新视图30次.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,我想知道是否有更有效的方法来更新我的主机容器中的VisualCollection内的DrawingVisuals.在我的viewmodel中的每个属性更改中,我发现,删除然后为该viewmodel重新添加一个新的DrawingVisual.随着不断移动的对象,我觉得应该有更好的方法,比如将DrawingVisuals本身直接绑定到viewmodel的属性,但是看起来会是什么样的？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.我开始关注这个例子： http://msdn.microsoft.com/en-us/library/ms742254.aspx

我故意避免DependencyProperties并将UserControls绑定到每个viewmodel,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和连接按钮和命令之外,我几乎不需要XAML.请问是否有些事情似乎不清楚或我遗漏了一些重要的事情.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];
    }
}

IVisuaModel impl：

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));
    }
}

IVisualFactory impl：

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;
    }
}