C sharp中button如何设置圆角

在C#中，可以使用以下代码来设置Button控件的圆角：

button1.FlatStyle = FlatStyle.Flat;
button1.FlatAppearance.BorderSize = 0;
button1.FlatAppearance.MouseDownBackColor = Color.Transparent;
button1.FlatAppearance.MouseOverBackColor = Color.Transparent;
button1.BackColor = Color.Red;
button1.Region = System.Drawing.Region.FromHrgn(CreateRoundRectRgn(0, 0, button1.Width, button1.Height, 20, 20));

其中，CreateRoundRectRgn() 是一个Win32 API函数，需要通过DllImport导入，代码如下：

[DllImport("Gdi32.dll", EntryPoint = "CreateRoundRectRgn")]
private static extern IntPtr CreateRoundRectRgn
(
    int nLeftRect,      // x-coordinate of upper-left corner
    int nTopRect,       // y-coordinate of upper-left corner
    int nRightRect,     // x-coordinate of lower-right corner
    int nBottomRect,    // y-coordinate of lower-right corner
    int nWidthEllipse,  // height of ellipse
    int nHeightEllipse  // width of ellipse
);

这段代码将Button控件的边框去掉，并且设置了Button的背景色和圆角。其中，Region属性是用来设置控件的形状的，通过FromHrgn方法将Win32 API函数创建的圆角区域设置为Button的形状。