A Single Instance Control Component in C#

Introduction

This article is on a Single Instance control component which checks whether any instance of your application is running on the system. One can use this component to check whether a particular application is running on the system, or to avoid multiple instances of your application running on the system. There are many methods with which you can prevent multiple instances of your application, like using complex Mutex class methods or some unmanaged code.

Here, I have used a simple Process class to check whether a particular process is running or not. Let's first discuss the InstanceControl component. The InstanceControl class is derived from the Component class of the .NET Framework, and this component has a method called IsAnyInstanceExist() which checks for a particular process running on the system and returns the status as true/false.

• Namespace: InstConLib
• Class: InstanceControl
• Members:
  • InstanceControl() (constructor which takes the process name)
  • IsAnyInstanceExist() (checks for the process and returns a bool value)

A brief description about the component members:

1. The InstanceControl(string) is the constructor of the InstanceControl component. The constructor takes a single parameter string which is the process name and stores it in the member variable.
2. The IsAnyInstanceExist() method of the InstanceControl component returns true/false by checking to see if the process is running or not. This method uses the Process class (alias System.Diagnostics.Process) and the GetProcessesByName() method which, in turn, returns the array of processes running with that name.

using System;
using System.Diagnostics;
using System.ComponentModel;

namespace InstConLib { 
/* InstanceControlLib Class controls the instance */

  public class InstanceControl: Component
  {
    private string stProcName=null;
    /*constructor which holds the application name*/
    public InstanceControl(string ProcName)
    {
      stProcName=ProcName;
    }
    public bool IsAnyInstanceExist()
    {  /*process class GetProcessesByName() checks for particular
      process is currently running and returns array of processes
      with that name*/
      Process[] processes = Process.GetProcessesByName(stProcName);
      
        if(processes.Length != 1)
          return false; /*false no instance exist*/
        else 
          return true; /*true mean instance exist*/
    }
  } /*end of class*/
}/*end of namespace*/

Compile the above as a component library to produce a .dll file. Then, you can call this component in different clients like WinForms, WebForms or Console applications. I have used a simple console application to use this component. The client program calls the InstanceControl component and uses its method. In this example, I used two instances of the component. One which will check for the process that is not running, and the other which checks for the process which is running in the system.

Following is the code snippet of the client application:

//InstClient.cs 

using System;
using InstConLib;
public class InstClient
{
  public static void Main()
  { 
   //First Object which looks for testApp.exe process  

   //remember its not neccessary to give extention of process

   InstConLib.InstanceControl in1 = new InstConLib.InstanceControl("testApp");
   if(in1.IsAnyInstanceExist())
    Console.WriteLine("Alreading one instance is running");
   else
    Console.WriteLine("No Instance running"); 
    //Second Object which looks for Explorer.exe process  

    //remember its not neccessary to give extention of process

    InstConLib.InstanceControl in2 = 
       new InstConLib.InstanceControl("Explorer");

   if(in2.IsAnyInstanceExist())
     Console.WriteLine("Alreading one instance is running");
   else
     Console.WriteLine("No Instance running");
 }
}

OUTPUT:

D:\vstudio>InstClient
No Instance running
Alreading one instance is running