C# 子窗口跟随父窗口且显示在最顶层

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从中可参考的知识点

1. 如何获得当前活动窗口

using System.Runtime.InteropServices;


 [DllImport("User32.dll")]
 public static extern IntPtr GetForegroundWindow();     //获取活动窗口句柄

 IntPtr hWnd = GetForegroundWindow();    //获取活动窗口句柄

 if (flg_AlarmWind_is_show == 0 && this.Handle == hWnd)
{
      AlarmWind.Location = new Point(this.Left, this.Top);
      AlarmWind.TopMost = true;
      AlarmWind.Show();
  }
flg_AlarmWind_is_show = 1;

2. 怎样将窗口放置最上层

 AlarmWind.TopMost = true;

3. 怎样改变窗口位置：

AlarmWind.Location = new Point(this.Left, this.Top);

思路

要显示在父窗口上层，不能被父窗口遮挡。但如果父窗口不再成为活动窗口（最小化或被其他进程窗口遮挡）时，子窗口又不能弹出。所以要判断当前活动窗口是不是父窗口，是则显示在最顶层，否则隐藏。

例程：

  private AlarmInfoWindow AlarmWind = new AlarmInfoWindow(); //为避免频繁创建，定义成全局的
       
        private int flg_AlarmWind_is_show = 0;

        public Form_EzHostCtrl()
        {
            InitializeComponent();                    
         
            creatTimerforAlarmShow();//定时器要随对象一起创建
        }
        public void Initial()
        {
            LoadPath();
            LayoutInitial();
        }
        private System.Timers.Timer AlarmWindShowTimer = new System.Timers.Timer();
        private void creatTimerforAlarmShow()
        {
            AlarmWindShowTimer.Interval = 50;
            AlarmWindShowTimer.Elapsed += AlarmWindShowTimer_Elapsed; //定时时间到的时候的回调函数
            AlarmWindShowTimer.AutoReset = true;//需要反复检测鼠标
            AlarmWindShowTimer.Enabled = true;  //启动定时器

        }

        [DllImport("User32.dll")]
        public static extern IntPtr GetForegroundWindow();     //获取活动窗口句柄

        /* 定时器回调函数 */
        private void AlarmWindShowTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            //如果鼠标在窗体边缘附近  
            if ((Cursor.Position.X - this.Left < 50 && Cursor.Position.X - this.Left > -50)
               || (Cursor.Position.X - this.Right < 50 && Cursor.Position.X - this.Right > -50)
               || (Cursor.Position.Y - this.Top < 50 && Cursor.Position.Y - this.Top > -50)
               || (Cursor.Position.Y - this.Bottom < 50 && Cursor.Position.Y - this.Bottom > -50))
            {
                IntPtr hWnd = GetForegroundWindow();    //获取活动窗口句柄
                
                if (flg_AlarmWind_is_show == 0 && this.Handle == hWnd)
                {
                    AlarmWind.Location = new Point(this.Left, this.Top);
                    AlarmWind.TopMost = true;
                    AlarmWind.Show();
                }
                flg_AlarmWind_is_show = 1;
            }
            else {
                AlarmWind.Hide();
                flg_AlarmWind_is_show = 0;
            }
        }