Step 1: Create a Window Application.
Step 2: Go -> To-> Program.cs file
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Step 3: Write this code in Main Method of Program.cs file.
//Add this line Program class.
private static Mutex m_Mutex;
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
//After that add below code
bool createdNew;
m_Mutex = new Mutex(true, "MyApplicationMutex", out createdNew);
if (createdNew)
Application.Run(new Form1());//Change the name of your startup form.
else
MessageBox.Show("The application is already running.", Application.ProductName,
MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
}
Step 4: After that build application and go -> Bin folder of your application and Go to-> Debug folder -> Click on Application exe.
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Single Instance means -> at a time only one application window open.
Output