怎么使一个winform中含有多个圆角的groupbox、textbox、richtectbox

要使一个 WinForm 中含有多个圆角的 GroupBox、TextBox、RichTextBox，可以通过以下步骤实现：

1. 创建一个新的类，继承自对应的控件类。例如，要创建一个圆角的 GroupBox，可以创建一个新的类，继承自 GroupBox。

public class RoundGroupBox : GroupBox
{
    // ...
}

2. 在新类的构造函数中设置控件的 BorderStyle 属性为 None，并设置控件的大小、颜色等属性。

public RoundGroupBox()
{
    this.BackColor = Color.Transparent;
    this.ForeColor = Color.White;
    this.Font = new Font("微软雅黑", 12F, FontStyle.Bold, GraphicsUnit.Point, ((byte)(134)));
    this.Size = new Size(200, 100);
    this.TabStop = false;
    this.FlatStyle = FlatStyle.Flat;
    this.BorderStyle = BorderStyle.None;
}

3. 重写控件的 OnPaint 方法，实现圆角效果。可以使用 Graphics 类的 DrawArc 和 FillPath 方法来绘制圆角。

protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);

    e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;

    using (GraphicsPath path = new GraphicsPath())
    {
        path.AddArc(new Rectangle(0, 0, 20, 20), 180, 90);
        path.AddLine(20, 0, this.Width - 20, 0);
        path.AddArc(new Rectangle(this.Width - 20, 0, 20, 20), -90, 90);
        path.AddLine(this.Width, 20, this.Width, this.Height - 20);
        path.AddArc(new Rectangle(this.Width - 20, this.Height - 20, 20, 20), 0, 90);
        path.AddLine(this.Width - 20, this.Height, 20, this.Height);
        path.AddArc(new Rectangle(0, this.Height - 20, 20, 20), 90, 90);
        path.AddLine(0, this.Height - 20, 0, 20);
        path.CloseFigure();

        this.Region = new Region(path);
    }

    using (Pen pen = new Pen(Color.FromArgb(255, 204, 204, 204), 1))
    {
        e.Graphics.DrawPath(pen, path);
    }
}

4. 在 WinForm 中使用新类替换原有的控件。

RoundGroupBox roundGroupBox1 = new RoundGroupBox();
roundGroupBox1.Location = new Point(50, 50);
roundGroupBox1.Text = "Round GroupBox";
this.Controls.Add(roundGroupBox1);

对于 TextBox 和 RichTextBox 控件，也可以采用类似的方法实现圆角效果。在 OnPaint 方法中使用 Graphics 类的 FillRectangle 方法绘制控件的背景，然后再使用 GraphicsPath 绘制圆角。

protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);

    e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;

    using (GraphicsPath path = new GraphicsPath())
    {
        path.AddArc(new Rectangle(0, 0, 20, 20), 180, 90);
        path.AddLine(20, 0, this.Width - 20, 0);
        path.AddArc(new Rectangle(this.Width - 20, 0, 20, 20), -90, 90);
        path.AddLine(this.Width, 20, this.Width, this.Height - 20);
        path.AddArc(new Rectangle(this.Width - 20, this.Height - 20, 20, 20), 0, 90);
        path.AddLine(this.Width - 20, this.Height, 20, this.Height);
        path.AddArc(new Rectangle(0, this.Height - 20, 20, 20), 90, 90);
        path.AddLine(0, this.Height - 20, 0, 20);
        path.CloseFigure();

        this.Region = new Region(path);
    }

    using (SolidBrush brush = new SolidBrush(Color.White))
    {
        e.Graphics.FillRectangle(brush, new Rectangle(0, 0, this.Width, this.Height));
    }

    using (Pen pen = new Pen(Color.FromArgb(255, 204, 204, 204), 1))
    {
        e.Graphics.DrawPath(pen, path);
    }
}