How do I get the title of the current active window using c#?

Question

See example on how you can do this with full source code here:

http://www.csharphelp.com/2006/08/get-current-window-handle-and-caption-with-windows-api-in-c/

[DllImport("user32.dll")]
static extern IntPtr GetForegroundWindow();

[DllImport("user32.dll")]
static extern int GetWindowText(IntPtr hWnd, StringBuilder text, int count);

private string GetActiveWindowTitle()
{
    const int nChars = 256;
    StringBuilder Buff = new StringBuilder(nChars);
    IntPtr handle = GetForegroundWindow();

    if (GetWindowText(handle, Buff, nChars) > 0)
    {
        return Buff.ToString();
    }
    return null;
}

---

Edited with @Doug McClean comments for better correctness.

If you were talking about WPF then use:

 Application.Current.Windows.OfType<Window>().SingleOrDefault(w => w.IsActive);

Based on GetForegroundWindow function | Microsoft Docs:

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
static extern IntPtr GetForegroundWindow();

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
static extern int GetWindowText(IntPtr hWnd, StringBuilder text, int count);

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
static extern int GetWindowTextLength(IntPtr hWnd);

private string GetCaptionOfActiveWindow()
{
    var strTitle = string.Empty;
    var handle = GetForegroundWindow();
    // Obtain the length of the text   
    var intLength = GetWindowTextLength(handle) + 1;
    var stringBuilder = new StringBuilder(intLength);
    if (GetWindowText(handle, stringBuilder, intLength) > 0)
    {
        strTitle = stringBuilder.ToString();
    }
    return strTitle;
}

It supports UTF8 characters.

Loop over Application.Current.Windows[] and find the one with IsActive == true.

Use the Windows API. Call GetForegroundWindow().

GetForegroundWindow() will give you a handle (named hWnd) to the active window.

Documentation: GetForegroundWindow function | Microsoft Docs