拖放需要数学修复

Question

我的 RichTextBox 在 Silverlight 4 中有拖放行为，但我遇到了一个小问题。

我希望用户能够“抓取” RichTextBox 的任何边框并拖放它。 RichTextBox 应该相对于用户“抓取”RichTextBox 的位置拖动。但是，一旦用户开始拖动，RichTextBox 就会“捕捉”到鼠标位置的中间，而不是保持相对于鼠标位置的位置。

所以如果我抓住右下角，如下所示...

https://skydrive.live.com/redir?resid=DCC93DD825EF3F43!658

它在拖动开始时“捕捉”到鼠标位置的中间，如下所示...

https://skydrive.live.com/redir?resid=DCC93DD825EF3F43!659

这是我的拖动代码。我假设我的数学是错误的（在 MouseMove 事件中）？？？

---

public class CustomRichTextBox : RichTextBox
{
    private bool isDragging = false;

    protected override void OnMouseLeftButtonDown(MouseButtonEventArgs e)
    {
        base.OnMouseLeftButtonDown(e);

        bool isDragAllowed = false;
        Point pt = e.GetPosition(this);

        if (pt.Y >= 0 && pt.Y <= this.BorderThickness.Top)
            // Allow dragging if the mouse is down on the top border
            isDragAllowed = true;
        else if (pt.Y >= (this.RenderSize.Height - this.BorderThickness.Bottom) && pt.Y <= this.RenderSize.Height)
            // Allow dragging if the mouse is down on the bottom border
            isDragAllowed = true;
        else if (pt.X >= 0 && pt.X <= this.BorderThickness.Left)
            // Allow dragging if the mouse is down on the left border
            isDragAllowed = true;
        else if (pt.X >= (this.RenderSize.Width - this.BorderThickness.Right) && pt.X <= this.RenderSize.Width)
            // Allow dragging if the mouse is down on the right border
            isDragAllowed = true;

        if (!isDragAllowed)
            return;

        this.CaptureMouse();
        isDragging = true;
    }

    protected override void OnMouseMove(MouseEventArgs e)
    {
        base.OnMouseMove(e);

        if (isDragging)
        {
            CustomRichTextBox elem = this;
            CompositeTransform ct = (CompositeTransform)elem.RenderTransform;
            UIElement parent = (UIElement)elem.Parent;

            ct.TranslateX = e.GetPosition(parent).X - (parent.RenderSize.Width / 2);
            ct.TranslateY = e.GetPosition(parent).Y - (parent.RenderSize.Height / 2);
        }
    }

    protected override void OnMouseLeftButtonUp(MouseButtonEventArgs e)
    {
        base.OnMouseLeftButtonUp(e);

        isDragging = false;
        this.ReleaseMouseCapture();
    }
}

Answer 1

这里缺少的是拖动开始位置的参考点。在鼠标移动事件中，您试图将控件转换为鼠标的当前位置，而不是 current 和 original 位置之间的增量。

或者通过使用相对坐标，您可以存储鼠标单击相对于控件的位置，然后在 OnMove 处将其从当前位置中减去。这就是下面示例中发生的情况。

请注意，这是没有 CompositeTransform 的 WPF。 减去父级的 RenderSize 对我来说似乎是一个错误，或者它可能是 WPF 和 Silverlight 的差异，无论如何我希望这有助于解决它：

public class CustomRichTextBox : RichTextBox
{
    private bool isDragging = false;
    private Point draggingPoint;

    protected override void OnPreviewMouseLeftButtonDown(MouseButtonEventArgs e)
    {
        base.OnPreviewMouseLeftButtonDown(e);

        bool isDragAllowed = false;
        Point pt = e.GetPosition(this);

        if (pt.Y >= 0 && pt.Y <= this.BorderThickness.Top)
            // Allow dragging if the mouse is down on the top border
            isDragAllowed = true;
        else if (pt.Y >= (this.RenderSize.Height - this.BorderThickness.Bottom) && pt.Y <= this.RenderSize.Height)
            // Allow dragging if the mouse is down on the bottom border
            isDragAllowed = true;
        else if (pt.X >= 0 && pt.X <= this.BorderThickness.Left)
            // Allow dragging if the mouse is down on the left border
            isDragAllowed = true;
        else if (pt.X >= (this.RenderSize.Width - this.BorderThickness.Right) && pt.X <= this.RenderSize.Width)
            // Allow dragging if the mouse is down on the right border
            isDragAllowed = true;

        if (!isDragAllowed)
            return;

        draggingPoint = pt;

        this.CaptureMouse();
        isDragging = true;
    }

    protected override void OnPreviewMouseMove(MouseEventArgs e)
    {
        base.OnPreviewMouseMove(e);

        if (isDragging)
        {
            CustomRichTextBox elem = this;
            TransformGroup ct = new TransformGroup();
            UIElement parent = (UIElement)elem.Parent;

            TranslateTransform tr = new TranslateTransform(
                e.GetPosition(parent).X - elem.RenderSize.Width + this.BorderThickness.Left - draggingPoint.X,
                e.GetPosition(parent).Y - elem.RenderSize.Height + this.BorderThickness.Top - draggingPoint.Y);

            ct.Children.Add(tr);

            elem.RenderTransform = ct;
        }
    }

    protected override void OnPreviewMouseLeftButtonUp(MouseButtonEventArgs e)
    {
        base.OnPreviewMouseLeftButtonUp(e);

        isDragging = false;
        this.ReleaseMouseCapture();
    }
}