用winform自定义一个边框颜色为黑白阴影的矩形可指定宽度的窗体控件

在Windows Form应用程序中，如果你想要自定义一个带有黑白阴影边缘效果的矩形控件，可以创建一个新的用户控件(UserControl)。以下是一个简单的步骤：

1. **新建UserControl**：
- 在Visual Studio中，右键点击项目 -> 添加 -> 新项 -> UserControl。
- 设计界面时，使用Graphics API绘制矩形并添加阴影效果。

public partial class CustomRectangle : UserControl
{
    public CustomRectangle()
    {
        InitializeComponent();

        // 创建画布
        var graphics = CreateGraphics();
        var pen = new Pen(Color.Black, 2); // 黑色线条

        // 绘制矩形
        using (pen)
            graphics.DrawRectangle(pen, ClientRectangle);

        // 绘制白色内阴影
        DrawInnerShadow(graphics);
        graphics.Dispose();
    }

    private void DrawInnerShadow(Graphics g)
    {
        int dx = 1, dy = 1; // 阴影偏移量
        float radius = 4f; // 阴影半径
        Color color = Color.White * 0.7f; // 白色阴影颜色

        for (int i = 0; i <= dx; i++)
        {
            int left = ClientRectangle.Left + i;
            int top = ClientRectangle.Top;
            int right = ClientRectangle.Right - i;
            int bottom = ClientRectangle.Bottom;

            using (var shadowPen = new Pen(color, 1))
                g.DrawLine(shadowPen, left, top, right, top);
            using (var shadowPen = new Pen(color, 1))
                g.DrawLine(shadowPen, right, top, right, bottom);
            using (var shadowPen = new Pen(color, 1))
                g.DrawLine(shadowPen, right, bottom, left, bottom);
            using (var shadowPen = new Pen(color, 1))
                g.DrawLine(shadowPen, left, bottom, left, top);

            if (i > 0)
            {
                using (var shadowPen = new Pen(color, 2))
                    g.DrawLine(shadowPen, left + radius, top, right - radius, top);
                using (var shadowPen = new Pen(color, 2))
                    g.DrawLine(shadowPen, right - radius, top, right - radius, bottom);
                using (var shadowPen = new Pen(color, 2))
                    g.DrawLine(shadowPen, left + radius, bottom, left + radius, top);
            }
        }

        for (int i = 0; i <= dy; i++)
        {
            int left = ClientRectangle.Left;
            int top = ClientRectangle.Top + i;
            int right = ClientRectangle.Right;
            int bottom = ClientRectangle.Bottom - i;

            using (var shadowPen = new Pen(color, 1))
                g.DrawLine(shadowPen, left, top, left, bottom);
            using (var shadowPen = new Pen(color, 1))
                g.DrawLine(shadowPen, right, top, right, bottom);
            using (var shadowPen = new Pen(color, 1))
                g.DrawLine(shadowPen, right, bottom, left, bottom);
            using (var shadowPen = new Pen(color, 1))
                g.DrawLine(shadowPen, left, bottom, left, top);

            if (i > 0)
            {
                using (var shadowPen = new Pen(color, 2))
                    g.DrawLine(shadowPen, left, top + radius, left, bottom - radius);
                using (var shadowPen = new Pen(color, 2))
                    g.DrawLine(shadowPen, right, top + radius, right, bottom - radius);
                using (var shadowPen = new Pen(color, 2))
                    g.DrawLine(shadowPen, left, top + radius, right, top + radius);
            }
        }
    }
}

现在你可以将这个自定义控件添加到任何Form中，并通过`Width`和`Height`属性指定其大小。记得在自定义控件的设计视图里设置适当的尺寸和约束，以便用户能够轻松调整。