Detect when a separate window in another process is opened or closed

You can use any of these options:

• Using the SetWinEventHook method
• Handling UI Automation events (preferred) (suggested by Hans in the comments )

Solution 1. Using the SetWinEventHook method

Using SetWinEventHook

, you can listen for some events from other processes and register a callback method WinEventProc

to receive the event when the event has occurred.

Here EVENT_SYSTEM_FOREGROUND

can help us.

We restrict the event receiver to receive this event from a specific process and then check if the text of the window that raises the event is equal Page Setup

, then we can say that the window Page Setup

in the target process is open, otherwise we can say that the dialog is Page Setup

not open.

For the sake of simplicity, in the example below, I've assumed the instance is notepad

open when the application starts, but you can also use Win32_ProcessStartTrace

to detect when the application starts notepad

.

To be more specific and tell when the dialog is closed, you can listen to EVENT_OBJECT_DESTROY

and determine if the message is for the window of interest.

public const uint EVENT_SYSTEM_FOREGROUND = 0x0003;
public const uint EVENT_OBJECT_DESTROY = 0x8001;
public const uint WINEVENT_OUTOFCONTEXT = 0;
public delegate void WinEventDelegate(IntPtr hWinEventHook, uint eventType, IntPtr hwnd,
    int idObject, int idChild, uint dwEventThread, uint dwmsEventTime);
[DllImport("user32.dll")]
public static extern IntPtr SetWinEventHook(uint eventMin, uint eventMax, IntPtr
    hmodWinEventProc, WinEventDelegate lpfnWinEventProc, uint idProcess,
    uint idThread, uint dwFlags);
[DllImport("user32.dll")]
public static extern bool UnhookWinEvent(IntPtr hWinEventHook);
[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
static extern int GetWindowText(IntPtr hWnd, StringBuilder lpString, int nMaxCount);

      

        
        
        
      

    

IntPtr hook = IntPtr.Zero;
protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);
    var p = System.Diagnostics.Process.GetProcessesByName("notepad").FirstOrDefault();
    if (p != null)
        hook = SetWinEventHook(EVENT_SYSTEM_FOREGROUND, EVENT_SYSTEM_FOREGROUND,
        IntPtr.Zero, new WinEventDelegate(WinEventProc), 
        (uint)p.Id, 0, WINEVENT_OUTOFCONTEXT);
}
protected override void OnFormClosing(FormClosingEventArgs e)
{
    UnhookWinEvent(hook);
    base.OnFormClosing(e);
}
void WinEventProc(IntPtr hWinEventHook, uint eventType,
    IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime)
{
    string s = "Page Setup";
    StringBuilder sb = new StringBuilder(s.Length + 1);
    GetWindowText(hwnd, sb, sb.Capacity);
    if (sb.ToString() == s)
        this.Text = "Page Setup is Open";
    else
        this.Text = "Page Setup is not open";
}

      

        
        
        
      

    

Solution 2: Handling UI Automation events

As Hans pointed out in the comments, you can use the UI Automation APIs to subscribe to WindowOpenedEvent

and WindowClosedEvent

.

In the example below, I assumed there was an open instance notepad

and found its dialog opening and closing Page Setup

:

protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);
    var notepad = System.Diagnostics.Process.GetProcessesByName("notepad")
                        .FirstOrDefault();
    if (notepad != null)
    {
        var notepadMainWindow = notepad.MainWindowHandle;
        var notepadElement = AutomationElement.FromHandle(notepadMainWindow);
        Automation.AddAutomationEventHandler(
            WindowPattern.WindowOpenedEvent, notepadElement,
            TreeScope.Subtree, (s1, e1) =>
            {
                var element = s1 as AutomationElement;
                if (element.Current.Name == "Page Setup")
                {
                    //Page setup opened.
                    this.Invoke(new Action(() =>
                    {
                        this.Text = "Page Setup Opened";
                    }));
                    Automation.AddAutomationEventHandler(
                        WindowPattern.WindowClosedEvent, element,
                        TreeScope.Subtree, (s2, e2) =>
                        {
                            //Page setup closed.
                            this.Invoke(new Action(() =>
                            {
                                this.Text = "Closed";
                            }));
                        });
                }
            });
    }
}

      

        
        
        
      

    

protected override void OnFormClosing(FormClosingEventArgs e)
{
    Automation.RemoveAllEventHandlers();
    base.OnFormClosing(e);
}

      

        
        
        
      

    

Don't forget to add assembly link UIAutomationClient

and UIAutomationTypes

and add using System.Windows.Automation;

.