Question

Note: There’s a very similar question, but it’s WPF-specific; this one is not.

How can I determine if the current application is activated (i.e. has focus)?

Answer 1

This works:

/// <summary>Returns true if the current application has focus, false otherwise</summary>
public static bool ApplicationIsActivated()
{
    var activatedHandle = GetForegroundWindow();
    if (activatedHandle == IntPtr.Zero) {
        return false;       // No window is currently activated
    }

    var procId = Process.GetCurrentProcess().Id;
    int activeProcId;
    GetWindowThreadProcessId(activatedHandle, out activeProcId);

    return activeProcId == procId;
}


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

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern int GetWindowThreadProcessId(IntPtr handle, out int processId);

It has the advantage of being thread-safe, not requiring the main form (or its handle) and is not WPF or WinForms specific. It will work with child windows (even independent ones created on a separate thread). Also, there’s zero setup required.

The disadvantage is that it uses a little P/Invoke, but I can live with that 🙂