WPF中我希望点击Canvas上的控件时，该控件动态加载虚线边框包裹住被点击的控件，该边框可以通过拖动四边来改变边框的大小，且被包裹的控件可以跟着动态变化空间大小。但是边框和控件在Canvas上的定位位置不变。在点击Canvas上空白处时，将包裹控件的边框消除掉，但是保留控件

您可以通过以下步骤实现上述功能：

1. 给每个控件添加一个事件处理程序，当鼠标单击控件时，动态地创建一个边框，并将该边框添加到Canvas上。

2. 在边框中添加四个可拖动的边框，使用户可以通过拖动边框来改变边框的大小。

3. 当边框大小发生改变时，动态地调整包裹控件的大小，使其与边框大小相同。

4. 在Canvas上添加一个事件处理程序，当鼠标单击空白处时，将边框从Canvas上移除，但是保留控件。

以下是示例代码：

private Border border = null;
private UIElement clickedElement = null;

private void Canvas_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    // 获取鼠标单击的控件
    clickedElement = e.Source as UIElement;

    // 如果控件不为空，则创建一个边框并将其添加到Canvas上
    if (clickedElement != null)
    {
        border = new Border()
        {
            BorderBrush = Brushes.Dashed,
            BorderThickness = new Thickness(1),
            Opacity = 0.7,
            IsHitTestVisible = false
        };

        Canvas.SetZIndex(border, int.MaxValue);

        canvas.Children.Add(border);

        // 获取控件在Canvas上的位置和大小
        Point position = clickedElement.TranslatePoint(new Point(0, 0), canvas);
        border.Width = clickedElement.RenderSize.Width;
        border.Height = clickedElement.RenderSize.Height;
        Canvas.SetLeft(border, position.X);
        Canvas.SetTop(border, position.Y);

        // 添加四个可拖动的边框
        AddResizeHandles();

        // 订阅SizeChanged事件，当边框大小改变时，动态地调整控件大小
        border.SizeChanged += Border_SizeChanged;
    }
}

private void Border_SizeChanged(object sender, SizeChangedEventArgs e)
{
    // 如果控件不为空，则根据边框的大小动态地调整控件的大小
    if (clickedElement != null)
    {
        clickedElement.Width = border.ActualWidth;
        clickedElement.Height = border.ActualHeight;
    }
}

private void AddResizeHandles()
{
    // 添加四个可拖动的边框
    AddResizeHandle(0, 0);
    AddResizeHandle(1, 0);
    AddResizeHandle(0, 1);
    AddResizeHandle(1, 1);
}

private void AddResizeHandle(double horizontalAlignment, double verticalAlignment)
{
    // 创建可拖动的边框
    Thumb thumb = new Thumb()
    {
        Width = 10,
        Height = 10,
        Background = Brushes.White,
        Opacity = 0.7,
        HorizontalAlignment = HorizontalAlignment.Stretch,
        VerticalAlignment = VerticalAlignment.Stretch
    };

    // 设置可拖动边框的位置和样式
    double left = horizontalAlignment * (border.Width - thumb.Width);
    double top = verticalAlignment * (border.Height - thumb.Height);
    Canvas.SetLeft(thumb, left);
    Canvas.SetTop(thumb, top);
    thumb.DragDelta += Thumb_DragDelta;

    // 将可拖动边框添加到边框上
    border.Children.Add(thumb);
}

private void Thumb_DragDelta(object sender, DragDeltaEventArgs e)
{
    // 获取可拖动边框
    Thumb thumb = sender as Thumb;

    // 如果可拖动边框不为空，则根据拖动的距离调整边框和控件的大小
    if (thumb != null)
    {
        double deltaHorizontal = Math.Max(thumb.Width, e.HorizontalChange);
        double deltaVertical = Math.Max(thumb.Height, e.VerticalChange);

        if (thumb.HorizontalAlignment == HorizontalAlignment.Left)
        {
            double newWidth = Math.Max(border.Width - deltaHorizontal, thumb.DesiredSize.Width);
            double newLeft = Canvas.GetLeft(border) + (border.Width - newWidth);
            border.Width = newWidth;
            Canvas.SetLeft(border, newLeft);

            if (clickedElement != null)
            {
                clickedElement.Width = newWidth;
            }
        }
        else
        {
            border.Width += deltaHorizontal;

            if (clickedElement != null)
            {
                clickedElement.Width += deltaHorizontal;
            }
        }

        if (thumb.VerticalAlignment == VerticalAlignment.Top)
        {
            double newHeight = Math.Max(border.Height - deltaVertical, thumb.DesiredSize.Height);
            double newTop = Canvas.GetTop(border) + (border.Height - newHeight);
            border.Height = newHeight;
            Canvas.SetTop(border, newTop);

            if (clickedElement != null)
            {
                clickedElement.Height = newHeight;
            }
        }
        else
        {
            border.Height += deltaVertical;

            if (clickedElement != null)
            {
                clickedElement.Height += deltaVertical;
            }
        }
    }
}

private void Canvas_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
    // 当鼠标释放时，移除边框
    if (border != null)
    {
        canvas.Children.Remove(border);
        border = null;
        clickedElement = null;
    }
}

在以上示例代码中，我们通过Canvas的MouseLeftButtonDown和MouseLeftButtonUp事件来实现单击控件时创建边框和单击空白处时移除边框的功能。同时，我们使用Thumb控件来实现可拖动的边框来改变边框的大小，使用SizeChanged事件来动态地调整控件的大小。