画布添加线条而不绘制它

Question

我目前正在尝试WPF，因为我以前使用过WinForms。我从一个小练习开始，想要创建一个程序，在你点击画布的地方划一条线。我以编程方式将该行添加到画布中，但似乎它没有绘制它。这些线条成为画布的孩子们。

C＃代码

DoEvents

XAML

private ArrayList arl = new ArrayList();

    private void Canvas_MouseDown(object sender, MouseButtonEventArgs e)
    {
        drawArea.Children.Clear();

        arl.Add(Mouse.GetPosition(drawArea));
        Point[] points = new Point[arl.Count];

        for (int i = 0; i < arl.Count; i++)
            points[i] = (Point)arl[i];

        Line[] lines = new Line[points.Length - 1];

        if(lines.Count() > 0)
        {
            for (int i = 0; i < lines.Length; i++)
            {
                lines[i] = new Line();
                lines[i].Stroke = SystemColors.WindowFrameBrush;

                lines[i].X1 = points[i + 1].X;
                lines[i].X2 = points[i].X;
                lines[i].Y1 = points[i + 1].Y;
                lines[i].Y2 = points[i].Y;
            }

            foreach (var item in lines)
                drawArea.Children.Add(item);
        }
    }