引用

/// <summary>
        /// 输入法切ENG
        /// </summary>
        public void ChangeENG() 
        {
            WinAPI.PostMessage(WinAPI.HWND_BROADCAST, WinAPI.WM_INPUTLANGCHANGEREQUEST, IntPtr.Zero, WinAPI.LoadKeyboardLayout(WinAPI.en_US, WinAPI.KLF_ACTIVATE));//输入法切换为ENGLISH,扫码枪需要
        }

        /// <summary>
        /// 输入法切Chinese
        /// </summary>
        public void ChangeChinese()
        {
            WinAPI.PostMessage(WinAPI.HWND_BROADCAST, WinAPI.WM_INPUTLANGCHANGEREQUEST, IntPtr.Zero, WinAPI.LoadKeyboardLayout(WinAPI.cn_ZH, WinAPI.KLF_ACTIVATE));//输入法切换为Chinese
        }

类：

/// <summary>
        /// 输入法切换
        /// </summary>
        public class WinAPI
        {
            [DllImport("user32.dll")]
            public static extern bool PostMessage(int hhwnd, uint msg, IntPtr wparam, IntPtr lparam);

            [DllImport("user32.dll")]
            public static extern IntPtr LoadKeyboardLayout(string pwszKLID, uint Flags);

            public static uint WM_INPUTLANGCHANGEREQUEST = 0x0050;
            public static int HWND_BROADCAST = 0xffff;
            public static string en_US = "00000409"; //英文
            public static string cn_ZH = "00000804";
            public static uint KLF_ACTIVATE = 1;
        }

C#中FormClosing与FormClosed的区别详细解析

C#中，当窗口关闭时，它会引发两个事件：Closing 和 Closed。

Closing 在窗口关闭之前引发，它提供一种机制，可以通过这种机制来阻止窗口关闭。 系统会向Closing 事件处理程序传递一个 FormClosingEventArgs e，该参数实现 Boolean Cancel 属性，将该属性设置为 true 可以阻止窗口关闭。

DialogResult result = MessageBox.Show("你确定要关闭吗！", "提示信息", MessageBoxButtons.OKCancel, MessageBoxIcon.Information);
            if (result == DialogResult.OK)
            {
                CloseDevice();
                ClosePLC();
                GC.Collect();
                //this.Close();
                this.Dispose();

                e.Cancel = false;
                
            }
            else
            {
                e.Cancel = true;
            }

在窗口真正关闭之前，会引发 Closed，这时无法阻止窗口关闭。

private void Form1_FormClosed(object sender, FormClosingEventArgs e)
        {
            Application.Exit();
        }