wpf - 扩展 WPF Toolkit 图表中的 LineSeries 以提供数据标签

Question

我复制了一个我发现的实现，它在 WPF Toolkit DataVisualization 的折线图上提供数据标签，并对其进行了一些更改。它显示数据点旁边的绘图值。图表会时不时地用不同的数据重新绘制自己，并且在发生这种情况时不会删除数据标签。

我覆盖RemoveDataPoint了基类中的方法以尝试从中删除，TextBlock但这Canvas会抛出一个InvalidOperationException（枚举器无效，因为集合已更改）。我了解为什么会发生异常，但是如何TextBlocks从Canvas相应的删除时DataPoint删除？这是我到目前为止所拥有的：

public class DataTagLineSeries : LineSeries
{
    private Canvas _labelsCanvas;

    private readonly Dictionary<DataPoint, TextBlock> _currentLabels = new Dictionary<DataPoint, TextBlock>();

    public bool DisplayLabels { get; set; }
    public string LabelBindingPath { get; set; }
    public Style LabelStyle { get; set; }
    public Point LabelOffset { get; set; }

    public override void OnApplyTemplate()
    {
        base.OnApplyTemplate();

        _labelsCanvas = (Canvas)GetTemplateChild("PlotArea");

        Clip = null;
    }

    protected override void UpdateDataPoint(DataPoint dataPoint)
    {
        base.UpdateDataPoint(dataPoint);

        if (DisplayLabels && dataPoint.Visibility == Visibility.Visible)
            Dispatcher.BeginInvoke(DispatcherPriority.Normal, (Action)(() => CreateLabel(dataPoint)));
    }

    protected override void RemoveDataPoint(DataPoint dataPoint)
    {
        base.RemoveDataPoint(dataPoint);

        if (_currentLabels.ContainsKey(dataPoint))
        {
            _labelsCanvas.Children.Remove(_currentLabels[dataPoint]);
            _currentLabels.Remove(dataPoint);
        }
    }

    private void CreateLabel(DataPoint dataPoint)
    {
        TextBlock label;

        if (_currentLabels.ContainsKey(dataPoint))
        {
            label = _currentLabels[dataPoint];
        }
        else
        {
            label = new TextBlock();

            _labelsCanvas.Children.Add(label);

            _currentLabels.Add(dataPoint, label);

            label.Style = LabelStyle;

            var binding = LabelBindingPath != null
                                    ? new Binding(LabelBindingPath) { Source = dataPoint.DataContext }
                                    : new Binding("DependentValue") { Source = dataPoint };

            BindingOperations.SetBinding(label, TextBlock.TextProperty, binding);
        }

        var coordinateY = Canvas.GetTop(dataPoint) + LabelOffset.Y;
        var coordinateX = Canvas.GetLeft(dataPoint) + LabelOffset.X;

        Canvas.SetTop(label, coordinateY);
        Canvas.SetLeft(label, coordinateX);
    }
}