c# - 用鼠标 move 矩形

Question

我写了这段代码:

private struct MovePoint
    {
        public int X;
        public int Y;
    }
private void Image_MouseDown(object sender, MouseEventArgs e)
    {
        FirstPoint = new MovePoint();
        FirstPoint.X = e.X;
        FirstPoint.Y = e.Y;
    }

    private void Image_MouseMove(object sender, MouseEventArgs e)
    {
        if(e.Button == MouseButtons.Left)
        {
            if(FirstPoint.X > e.X)
            {
                Rectangle.X = FirstPoint.X - e.X;
                //Rectangle.Width -= FirstPoint.X - e.X;
            } else
            {
                Rectangle.X = FirstPoint.X + e.X;
                //Rectangle.Width += FirstPoint.X + e.X;
            }

            if(FirstPoint.Y > e.Y)
            {
                Rectangle.Y = FirstPoint.Y - e.Y;
                //Rectangle.Height -= FirstPoint.Y - e.Y;
            } else
            {
                Rectangle.Y = FirstPoint.Y + e.Y;
                //Rectangle.Height += FirstPoint.Y + e.Y;
            }

            Image.Invalidate();
        }
    }
private void Image_Paint(object sender, PaintEventArgs e)
    {
        if(Pen != null) e.Graphics.DrawRectangle(Pen, Rectangle);
    }

矩形 move ，但有反转(不应该)。你能帮忙吗？

Answer 1

鼠标 move 处理程序中用于根据鼠标 move move 矩形的数学运算似乎很不合理；我想你想要这样的东西:

private void Image_MouseMove(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        int initialX = 0, initialY = 0; // for example.

        Rectangle.X = (e.X - FirstPoint.X) + initialX; 
        Rectangle.Y = (e.Y - FirstPoint.Y) + initialY;

        Image.Invalidate();
    }
}

这样，矩形的左上角将通过跟踪初始 鼠标按下位置和当前 鼠标位置之间的增量来跟随鼠标。但请注意，每次您重新单击并拖动时，矩形都会移回其原始位置。

相反，如果您希望 Rectangle 在多次点击和拖动操作中“记住”它的位置(即不在按下鼠标时重新初始化到它的初始位置)，您可以这样做:

private void Image_MouseMove(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        // Increment rectangle-location by mouse-location delta.
        Rectangle.X += e.X - FirstPoint.X; 
        Rectangle.Y += e.Y - FirstPoint.Y; 

        // Re-calibrate on each move operation.
        FirstPoint = new MovePoint { X = e.X, Y = e.Y };

        Image.Invalidate();
    }
}

另一个建议:当已有 System.Drawing.Point 类型时，无需创建您自己的 MovePoint 类型。另外，一般来说，尽量不要创建可变结构。