c# – 在处理多个文本框的get和lost焦点事件时,重复事件调用和焦

private void Form1_Load(object sender,EventArgs e)
    {

        foreach (Control c in this.Controls)
        {
            if (c is TextBox)
            {
                c.GotFocus += new System.EventHandler(this.txtGotFocus);
                c.LostFocus += new System.EventHandler(this.txtLostfocus);
            }
        }
    }
    private void txtGotFocus(object sender,EventArgs e)
    {
        TextBox tb = (TextBox)sender;
        if (tb != null)
        {
            tb.BackColor = Color.Silver;
            tb.BorderStyle = BorderStyle.FixedSingle;
        }

    }
    private void txtLostFocus(object sender,EventArgs e)
    {

        TextBox tb = (TextBox)sender;
        if (tb != null)
        {
            tb.BackColor = Color.White;
            tb.BorderStyle = BorderStyle.Fixed3D;
        }
    }

它可以在第一个文本框中正常工作,但是当我按Tab键转到下一个文本框时,它将重复调用这两个事件,文本框的行为就像闪烁一样.一段时间后错误信息显示在代码中：

A callback was made on a garbage collected delegate of type ‘System.Windows.Forms!System.Windows.Forms.NativeMethods+WndProc::Invoke’. This may cause application crashes,corruption and data loss. When passing delegates to unmanaged code,they must be kept alive by the managed application until it is guaranteed that they will never be called.

代码有什么问题？有什么解决方案吗？