THECODEPROGRAM

Let's get started.

Firstly we need to add below library in our namespace:

using System.Runtime.InteropServices;

• GetForeGroundWindow() method will get the information and related addresses of windows which is foreground. It means it will get the information of active window.
• GetWindowsText() method will get the title text of the specified window via information which provided by GetForeGroundWindow() method.

Now define GetForeGroundWindow() and GetWindowsText() from user32.dll inside the class which will be called.

        [DllImport("user32.dll")]
        static extern IntPtr GetForegroundWindow();
        [DllImport("user32.dll")]
        static extern int GetWindowText(IntPtr hwnd, StringBuilder ss, int count);

Below code block will get the title of active window. Below method will first get active window and assign it to a pointer variable. Then via this pointer it will get the title text of active window. Then it will return the title as string.

 private string ActiveWindowTitle()
        {
            //Create the variable
            const int nChar = 256;
            StringBuilder ss = new StringBuilder(nChar);
            
            //Run GetForeGroundWindows and get active window informations
            //assign them into handle pointer variable
            IntPtr handle = IntPtr.Zero;
            handle = GetForegroundWindow();

            if (GetWindowText(handle, ss, nChar) > 0) return ss.ToString();
            else return "";
        }

Now I will see the active windows time by time. To perform this I have created a Timer and in Tick event of this timer, At tick event we have recorded the active titles inside a Listbox with their time values.

        public Form1()
        {
            InitializeComponent();

            this.TopMost = true;

            Timer tmr = new Timer();
            tmr.Interval = 1000;
            tmr.Tick += Tmr_Tick;
            tmr.Start();
        }

        private void Tmr_Tick(object sender, EventArgs e)
        {
            //get title of active window
            string title = ActiveWindowTitle();
            //check if it is null and add it to list if correct
            if (title != "")
            {
                lbActiveWindows.Items.Add( DateTime.Now.ToString("hh:mm:ss") + " - " + title);
            }
        }

Run the program and switch between the screens. Then you will see the switched screens inside listbox.

• We used system APIs inside our C# program.
• We called system DLL's (Dynamic Library Link) in this project.
• We get active window informations including address pointer of active window.

That is all in this article.

You can reach the example project on Github via below link:
https://github.com/thecodeprogram/GetActiveWindow

Burak Hamdi TUFAN