How can I find the active child window?

Question

How can I find the active child window (like focus Edit in modal dialog). I know how to enumerate child windows, but I don't know how to detect if a child window is active (focus).

Answer 1

If you are looking for the active child window of a different process, then you can match the IntPtr to the child window to the IntPtr from

  [DllImport("User32")]
  public static extern IntPtr GetForegroundWindow();

If this is not what you are looking for, could you please elaborate a little on your problem.

Answer 2

If you are speaking about Mdi child windows, you can use ActiveMdiChild, which is a property of the form class (use it on your mdiparent).

If you are speaking about focused controls, you can get using ActiveControl, which is a property of every container control (e.g. all your forms)

Answer 3

I have got answer after trying more than 2 hour with google...this is what i ahve got

StringBuilder builder = new StringBuilder(500);

int foregroundWindowHandle = GetForegroundWindow();

uint remoteThreadId = GetWindowThreadProcessId(foregroundWindowHandle, 0);

uint currentThreadId = GetCurrentThreadId();

//AttachTrheadInput is needed so we can get the handle of a focused window in another app

AttachThreadInput(remoteThreadId, currentThreadId, true);

//Get the handle of a focused window

int focused = GetFocus();

//Now detach since we got the focused handle

AttachThreadInput(remoteThreadId, currentThreadId, false);

As we have the handle of the focus window we could get it name/Class and also other necessary information

In this case i just find out the class name

StringBuilder winClassName = new StringBuilder();

int numChars = CustomViewAPI.Win32.GetClassName((IntPtr)focused, winClassName, winClassName.Capacity);

Answer 4

Basically it's just a simple Linq query:

      var active = (from form in Application.OpenForms.OfType<Form>()
                    where form.Focused
                    select form).FirstOrDefault();

Where active can be null or a form. Just a short example with few forms:

class Program
{
  static void Main(string[] args)
  {
    for (int i = 0; i < 10; i++)
    {
      Form sample = new Form();
      sample.Text = i.ToString();
      sample.Show();
    }

    while (true)
    {
      var active = (from form in Application.OpenForms.OfType<Form>()
                    where form.Focused
                    select form).FirstOrDefault();

      if (active != null)
        Console.Write(active.Text);

      Application.DoEvents();
      Thread.Sleep(100);
    }

  }
}