如何在windows窗体中单击窗体后删除按钮上的黑色轮廓

button1.FlatStyle = FlatStyle.Flat; // 或者 FlatStyle.Popup

public class MyButton : Button
{
    protected override void OnPaint(PaintEventArgs pevent)
    {
        base.OnPaint(pevent);
        // 在这里自定义按钮的绘制逻辑，不绘制黑色轮廓
    }
}

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        Application.AddMessageFilter(new ButtonFocusMessageFilter());
    }
}

public class ButtonFocusMessageFilter : IMessageFilter
{
    private const int WM_SETFOCUS = 0x0007;

    public bool PreFilterMessage(ref Message m)
    {
        if (m.Msg == WM_SETFOCUS)
        {
            Control focusedControl = Control.FromHandle(m.WParam);
            if (focusedControl is Button)
            {
                // 按钮获得焦点时，取消焦点，去除黑色轮廓
                focusedControl.Parent.Focus();
                return true;
            }
        }
        return false;
    }
}