C#窗体越界时鼠标还能回到初始坐标位置

对窗体加越界限制后，鼠标拖动窗体越界时，窗体不能动，鼠标位置可动，但窗体不再越界时，鼠标位置还能回到鼠标按下时相对窗体的坐标：
1、首先创建一个窗体form1，然后在窗体上拖一个button1按钮（主要通过这个按钮来拖动窗体）

2、然后对按钮添加鼠标按下事件、鼠标移动事件和鼠标抬起事件，事件里面是对窗体和鼠标坐标的操作，整体代码如下：
using system.drawing;
using system.windows.forms;
namespace 窗体越界鼠标还能回到初始坐标
{
    public partial class form1 : system.windows.forms.form
    {
        #region 变量定义
        public point mainformposition;//主窗口左上角位置
        int workingareaheight = systeminformation.workingarea.height;
        int workingareawidth = systeminformation.workingarea.width;
        private point relativetmouseposition;//鼠标相对窗体的相对坐标
        bool firstleft = false;//是否左边第一次按下时坐标
        bool firstright = false;//是否右边第一次按下时坐标
        bool firstup = false;//是否上边第一次按下时坐标
        bool firstdown = false;//是否下边第一次按下时坐标
        bool isfirstdown = true;//是否第一次按下，鼠标越界纠正时判断是否是第一次按下，不是按下后又拖动了
        bool ismoveout = false;//是否拖出
        //这两个变量做差，差值为拖出的距离时软件弹出侧边
        int oldmove_x = 0;//侧边停靠拖出时起始坐标
        //上一个时刻、鼠标的位置
        private point oldmouseposition;
        //当前时刻、鼠标的位置
        private point currentmouseposition;
        //鼠标事件
        [system.runtime.interopservices.dllimport("user32")]
        private static extern int mouse_event(int dwflags, int dx, int dy, int cbuttons, int dwextrainfo);
        //移动鼠标
        const int mouseeventf_move = 0x0001;
        //模拟鼠标左键按下
        const int mouseeventf_leftdown = 0x0002;
        //模拟鼠标左键抬起
        const int mouseeventf_leftup = 0x0004;
        //模拟鼠标右键按下
        const int mouseeventf_rightdown = 0x0008;
        //模拟鼠标右键抬起
        const int mouseeventf_rightup = 0x0010;
        //模拟鼠标中键按下
        const int mouseeventf_middledown = 0x0020;
        //模拟鼠标中键抬起
        const int mouseeventf_middleup = 0x0040;
        //标示是否采用绝对坐标
        const int mouseeventf_absolute = 0x8000;
        #endregion

        #region 窗体初始化
        public form1()
        {
            initializecomponent();
        }
        #endregion

        //-------------------------按钮button1鼠标事件---------------------------------------------------------------
        #region 鼠标左键按下button1按钮事件
        private void button1_mousedown(object sender, mouseeventargs e)
        {
            if (e.button == mousebuttons.left)
            {
                currentmouseposition = control.mouseposition;
                oldmouseposition = currentmouseposition;   //鼠标按下时、两个时刻的坐标变成一样，防止错误移动            
                mainformposition = location;
                if (isfirstdown)//鼠标按下时，记录第一次鼠标按下相对主窗体的坐标
                {
                    relativetmouseposition.x = currentmouseposition.x - location.x;
                    relativetmouseposition.y = currentmouseposition.y - location.y;
                    isfirstdown = false;
                }
                if (ismoveout)//鼠标按下时，记录拖出时的初始坐标
                {
                    oldmove_x = currentmouseposition.x;
                }
            }
        }
        #endregion

        #region 鼠标左键按住button1按钮移动事件
        private void button1_mousemove(object sender, mouseeventargs e)
        {
            if (e.button == mousebuttons.left)
            {
                currentmouseposition = control.mouseposition;
                if (currentmouseposition.x < relativetmouseposition.x && currentmouseposition.y > relativetmouseposition.y && currentmouseposition.y < workingareaheight - this.clientsize.height + relativetmouseposition.y)//左边窗体越界坐标纠正
                {
                    mainformposition.x = 0;
                    mainformposition.y += currentmouseposition.y - oldmouseposition.y;
                    //保存上一个时刻的鼠标位置
                    oldmouseposition.y = currentmouseposition.y;
                    firstleft = true;
                }
                else if (currentmouseposition.x > workingareawidth - this.clientsize.width + relativetmouseposition.x && currentmouseposition.y > relativetmouseposition.y && currentmouseposition.y < workingareaheight - this.clientsize.height + relativetmouseposition.y)//右边窗体越界坐标纠正
                {
                    mainformposition.x = workingareawidth - this.clientsize.width;
                    mainformposition.y += currentmouseposition.y - oldmouseposition.y;
                    //保存上一个时刻的鼠标位置
                    oldmouseposition.y = currentmouseposition.y;
                    firstright = true;
                }
                else if (currentmouseposition.y < relativetmouseposition.y && currentmouseposition.x > relativetmouseposition.x && currentmouseposition.x < workingareawidth - this.clientsize.width + relativetmouseposition.x)//上边窗体越界坐标纠正
                {
                    mainformposition.y = 0;
                    mainformposition.x += currentmouseposition.x - oldmouseposition.x;
                    //保存上一个时刻的鼠标位置
                    oldmouseposition.x = currentmouseposition.x;
                    firstup = true;
                }
                else if (currentmouseposition.y > workingareaheight - this.clientsize.height + relativetmouseposition.y && currentmouseposition.x > relativetmouseposition.x && currentmouseposition.x < workingareawidth - this.clientsize.width + relativetmouseposition.x)//下边窗体越界坐标纠正
                {
                    mainformposition.y = workingareaheight - this.clientsize.height;
                    mainformposition.x += currentmouseposition.x - oldmouseposition.x;
                    //保存上一个时刻的鼠标位置
                    oldmouseposition.x = currentmouseposition.x;
                    firstdown = true;
                }
                else if (currentmouseposition.x < relativetmouseposition.x && currentmouseposition.y < relativetmouseposition.y)//左上角窗体越界坐标纠正
                {
                    mainformposition.x = 0;
                    mainformposition.y = 0;
                    mainformposition.x += currentmouseposition.x - oldmouseposition.x;
                    mainformposition.y += currentmouseposition.y - oldmouseposition.y;
                    //保存上一个时刻的鼠标位置
                    oldmouseposition.x = currentmouseposition.x;
                    oldmouseposition.y = currentmouseposition.y;
                    firstleft = true;
                    firstup = true;
                }
                else if (currentmouseposition.x > workingareawidth - this.clientsize.width + relativetmouseposition.x && currentmouseposition.y < relativetmouseposition.y)//右上角窗体越界坐标纠正
                {
                    mainformposition.x = workingareawidth - this.clientsize.width;
                    mainformposition.y = 0;
                    mainformposition.x += currentmouseposition.x - oldmouseposition.x;
                    mainformposition.y += currentmouseposition.y - oldmouseposition.y;
                    //保存上一个时刻的鼠标位置
                    oldmouseposition.x = currentmouseposition.x;
                    oldmouseposition.y = currentmouseposition.y;
                    firstright = true;
                    firstup = true;
                }
                else if (currentmouseposition.x < relativetmouseposition.x && currentmouseposition.y > workingareaheight - this.clientsize.height + relativetmouseposition.y)//左下角窗体越界坐标纠正
                {
                    mainformposition.x = 0;
                    mainformposition.y = workingareaheight - this.clientsize.height;
                    mainformposition.x += currentmouseposition.x - oldmouseposition.x;
                    mainformposition.y += currentmouseposition.y - oldmouseposition.y;
                    //保存上一个时刻的鼠标位置
                    oldmouseposition.x = currentmouseposition.x;
                    oldmouseposition.y = currentmouseposition.y;
                    firstleft = true;
                    firstdown = true;
                }
                else if (currentmouseposition.x > workingareawidth - this.clientsize.width + relativetmouseposition.x && currentmouseposition.y > workingareaheight - this.clientsize.height + relativetmouseposition.y)//右下角窗体越界坐标纠正
                {
                    mainformposition.y = workingareaheight - this.clientsize.height;
                    mainformposition.x = workingareawidth - this.clientsize.width;
                    mainformposition.x += currentmouseposition.x - oldmouseposition.x;
                    mainformposition.y += currentmouseposition.y - oldmouseposition.y;
                    //保存上一个时刻的鼠标位置
                    oldmouseposition.x = currentmouseposition.x;
                    oldmouseposition.y = currentmouseposition.y;
                    firstright = true;
                    firstdown = true;
                }
                if (firstleft)
                {
                    currentmouseposition.x = relativetmouseposition.x;
                    firstleft = false;
                }
                if (firstright)
                {
                    currentmouseposition.x = workingareawidth - this.clientsize.width + relativetmouseposition.x;
                    firstright = false;
                }
                if (firstup)
                {
                    currentmouseposition.y = relativetmouseposition.y;
                    firstup = false;
                }
                if (firstdown)
                {
                    currentmouseposition.y = workingareaheight - this.clientsize.height + relativetmouseposition.y;
                    firstdown = false;
                }
                if (firstleft && firstup)
                {
                    currentmouseposition.x = relativetmouseposition.x;
                    currentmouseposition.y = relativetmouseposition.y;
                    firstleft = false;
                    firstup = false;

                }
                if (firstright && firstup)
                {
                    currentmouseposition.x = workingareawidth - this.clientsize.width + relativetmouseposition.x;
                    currentmouseposition.y = relativetmouseposition.y;
                    firstup = false;
                    firstright = false;
                }
                if (firstleft && firstdown)
                {
                    currentmouseposition.x = relativetmouseposition.x;
                    currentmouseposition.y = workingareaheight - this.clientsize.height + relativetmouseposition.y;
                    firstleft = false;
                    firstdown = false;
                }
                if (firstright && firstdown)
                {
                    currentmouseposition.x = workingareawidth - this.clientsize.width + relativetmouseposition.x;
                    currentmouseposition.y = workingareaheight - this.clientsize.height + relativetmouseposition.y;
                    firstright = false;
                    firstdown = false;
                }
                //对窗体进行移动
                mainformposition.x += currentmouseposition.x - oldmouseposition.x;
                mainformposition.y += currentmouseposition.y - oldmouseposition.y;
                //保存上一个时刻的鼠标位置
                oldmouseposition = currentmouseposition;

                #region 越界处理
                if (mainformposition.x < 0)//左边越界
                {
                    mainformposition.x = 0;
                }
                else if (mainformposition.y < 0)//上边越界
                {
                    mainformposition.y = 0;
                }
                else if (mainformposition.x > workingareawidth - this.clientsize.width)//右边越界
                {
                    mainformposition.x = workingareawidth - this.clientsize.width;
                }
                else if (mainformposition.y > workingareaheight - this.clientsize.height)//下边越界
                {
                    mainformposition.y = workingareaheight - this.clientsize.height;
                }
                //更新主窗口位置
                location = mainformposition;
                #endregion
            }
        }
        #endregion

        #region 鼠标在按钮button1抬起事件
        private void button1_mouseup(object sender, mouseeventargs e)
        {
            isfirstdown = true;
            //如果主窗体在这个位置，就判断允许主窗体在鼠标抬起后执行移动事件
            if (mainformposition.x == workingareawidth - this.clientsize.width)
            {
                ismoveout = false;
            }
            if (mainformposition.x == 0)
            {
                ismoveout = false;
            }
        }
        #endregion
    }
}

动画效果如下：

 

这是本人在一个项目中遇到的问题，所以特意总结出来分享给大家。