为控件大小创建边界

Question

我正在创建一个标签控件，允许从标签的顶部和底部调整大小。它也只在移动时垂直滑动。我为它的运动和可调整大小的标签的底部创建了边界，但是我很难弄清楚我在顶部做错了什么。只要将鼠标从顶部拖出边界之外，它就会触发450像素的预设长度。我正在使用.SetBounds和Math.Min。

using System;
using System.Drawing;
using System.Windows.Forms;

namespace EventTest
{
    public partial class Form1 : Form
    {
        Point label1_MousePoint_01 = new Point();
        Point label1_Start_01 = new Point();
        Point label1_End_01 = new Point();
        int label1_MouseSwitch_01;

        public Form1()
        {
            InitializeComponent();
            label1.MouseDown += Label1_MouseDown;
            label1.MouseUp += Label1_MouseUp;
            label1.MouseMove += Label1_MouseMove;
        }

        // Mouse Move Event
        private void Label1_MouseMove(object sender, MouseEventArgs e)
        {
            if ((e.X < label1.Width && e.X > 0 && e.Y > 0 && e.Y < 4) || (e.X < label1.Width && e.X > 0 && e.Y > label1.Height - 4 && e.Y < label1.Height))
            {
                Cursor.Current = Cursors.SizeNS;
            }

            // Mouse Event Top Move
            if (label1_MouseSwitch_01 == 1)
            {
                label1.SetBounds(0, Math.Max(e.Y + label1.Location.Y - label1_MousePoint_01.Y, 40), 120, Math.Min(label1.Height - e.Y + label1_MousePoint_01.Y, 450));
            }

            // Mouse Event Bottom Move
            else if (label1_MouseSwitch_01 == 2)
            {
                label1.Height = Math.Min(660 - label1.Location.Y, e.Location.Y);
            }

            // Mouse Event Grab and Move
            else if (label1_MouseSwitch_01 == 3)
            {
                int ny = Math.Min(Math.Max((label1.Location.Y - label1_MousePoint_01.Y + e.Y), 40), 660 - label1.Height);
                label1.Location = new Point(0, ny);
            }
        }

        // Mouse Up Event
        private void Label1_MouseUp(object sender, MouseEventArgs e)
        {
            label1_MouseSwitch_01 = 0;

            if (label1.Height < 20)
            {
                label1.Height = 20;
            }
        }

        // Mouse Down Event
        private void Label1_MouseDown(object sender, MouseEventArgs e)
        {
            label1_Start_01.Y = label1.Height;
            label1_End_01.Y = label1.Top;

            // Set Mouse Switch
            if (e.Button == MouseButtons.Left)
            {
                label1_MousePoint_01 = e.Location;

                if (e.Y > 0 && e.Y < 4)
                {
                    Cursor.Current = Cursors.SizeNS;
                    label1_MouseSwitch_01 = 1;
                }

                else if (e.Y > label1.Height - 4 && e.Y < label1.Height)
                {
                    Cursor.Current = Cursors.SizeNS;
                    label1_MouseSwitch_01 = 2;
                }

                else if (e.Y > 4 && e.Y < label1.Height - 4)
                {
                    label1_MouseSwitch_01 = 3;
                }
            }
        }

        // Snap To Every 20 Pixels 
        public int RoundEr(int i)
        {
            return ((int)Math.Round(i / 20.0)) * 20;
        }
    }
}