OnCustomCommand executes when the Service Control Manager (SCM) passes a custom command to the service. Specifies actions to take when a command with the specified parameter value occurs.

The only values for a custom command that you can define in your application or use in OnCustomCommand are those between 128 and 256.
Integers below 128 correspond to system-reserved values.

Create One Windows Service & Implement Below Code in Service :

namespace MyWindowsService
{
    public partial class Service1 : ServiceBase
    {
        public enum SimpleServiceCustomCommands { Command1 = 128, Command2 =129, Command3 = 130};
 
        public Service1()
        {
            InitializeComponent();
        }

protected override void OnStart(string[] args)
        {
        }

protected override void OnStop()
        {
        }

protected override void OnCustomCommand(int command)
        {
            base.OnCustomCommand(command);

switch(command)
            {
                case(int)SimpleServiceCustomCommands.Command1:
                //Command1 Implementation
                break;

case(int)SimpleServiceCustomCommands.Command2:
                //Command2 Implementation
                 break;

case(int)SimpleServiceCustomCommands.Command3:
                //Command3 Implementation
                    break;
                default:
                    break;
 
           }       
        }
    } }

Call Windows Service CustomCommands From User Application :

• Create Service Controller Object

  ServiceController Controller = new ServiceController("MyWindowsService");

• Start the Windows Service

  Controller.Refresh(); //Gets the current status of service
      if (Controller.Status == ServiceControllerStatus.Stopped)
       {
   Controller.Start();
       }

• Call CustomCommands Using Controller Object
   

  if (Controller.Status == ServiceControllerStatus.Running)
    {
        Controller.ExecuteCommand(128); 
       }