C#: Detecting which application has focus

Question

I'm looking to create a C# application that changes content according to which application currently has focus. So if the user is using Firefox, my app would know that. Same for Chrome, Visual Studio, TweetDeck etc.

Is this possible, and if so - how would I go about achieving it?

I have a feeling I'm asking for to much - but it's worth a try.

Many thanks in advance.

Answer 1

This can be done in pure .NET using the Automation framework that is part of the WPF. Add references to UIAutomationClient and UIAutomationTypes and use Automation.AddAutomationFocusChangedEventHandler, e.g.:

public class FocusMonitor
{
    public FocusMonitor()
    {
        AutomationFocusChangedEventHandler focusHandler = OnFocusChanged;
        Automation.AddAutomationFocusChangedEventHandler(focusHandler);
    }

    private void OnFocusChanged(object sender, AutomationFocusChangedEventArgs e)
    {
        AutomationElement focusedElement = sender as AutomationElement;
        if (focusedElement != null)
        {
            int processId = focusedElement.Current.ProcessId;
            using (Process process = Process.GetProcessById(processId))
            {
                Debug.WriteLine(process.ProcessName);
            }
        }
    }
}