Clipboard change notification?

Question

I know how put content to and retrieve content from the clipboard.

However, between these two operations, it is possible for another operation to change the content of the clipboard.

Is there a way to be notified when any application modifies the clipboard?

Answer 1

I know this answer is to late The only reference you need to add is to windows froms in your wpf application. I created a wrapper to the functionality I found on the internet. Most of the examples do more stuff than what I needed so I desided to create my own class. I like to isolate the problems so this class just listens when the clipboard changes and tels you the type of data that is on the clipboard. For example is it text? an image? or what?

Anyways here is my wrapper:

using System;
using System.Windows.Forms;
using System.Threading;
using System.Runtime.InteropServices;

public static class ClipboardMonitor 
{
    public delegate void OnClipboardChangeEventHandler(ClipboardFormat format, object data);
    public static event OnClipboardChangeEventHandler OnClipboardChange;

    public static void Start()
    {
        ClipboardWatcher.Start();
        ClipboardWatcher.OnClipboardChange += (ClipboardFormat format, object data) =>
        {
            if (OnClipboardChange != null)
                OnClipboardChange(format, data);
        };
    }

    public static void Stop()
    {
        OnClipboardChange = null;
        ClipboardWatcher.Stop();
    }

    class ClipboardWatcher : Form
    {
        // static instance of this form
        private static ClipboardWatcher mInstance;

        // needed to dispose this form
        static IntPtr nextClipboardViewer;

        public delegate void OnClipboardChangeEventHandler(ClipboardFormat format, object data);
        public static event OnClipboardChangeEventHandler OnClipboardChange;

        // start listening
        public static void Start()
        {
            // we can only have one instance if this class
            if (mInstance != null)
                return;

            Thread t = new Thread(new ParameterizedThreadStart(x =>
            {
                Application.Run(new ClipboardWatcher());
            }));
            t.SetApartmentState(ApartmentState.STA); // give the [STAThread] attribute
            t.Start();
        }

        // stop listening (dispose form)
        public static void Stop()
        {
            mInstance.Invoke(new MethodInvoker(() =>
            {
                ChangeClipboardChain(mInstance.Handle, nextClipboardViewer);
            }));
            mInstance.Invoke(new MethodInvoker(mInstance.Close));

            mInstance.Dispose();

            mInstance = null;
        }

        // on load: (hide this window)
        protected override void SetVisibleCore(bool value)
        {
            CreateHandle();

            mInstance = this;

            nextClipboardViewer = SetClipboardViewer(mInstance.Handle);

            base.SetVisibleCore(false);
        }

        [DllImport("User32.dll", CharSet = CharSet.Auto)]
        public static extern IntPtr SetClipboardViewer(IntPtr hWndNewViewer);

        [DllImport("User32.dll", CharSet = CharSet.Auto)]
        public static extern bool ChangeClipboardChain(IntPtr hWndRemove, IntPtr hWndNewNext);

        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        public static extern int SendMessage(IntPtr hwnd, int wMsg, IntPtr wParam, IntPtr lParam);

        // defined in winuser.h
        const int WM_DRAWCLIPBOARD = 0x308;
        const int WM_CHANGECBCHAIN = 0x030D;

        protected override void WndProc(ref Message m)
        {
            switch (m.Msg)
            {
                case WM_DRAWCLIPBOARD:
                    ClipChanged();
                    SendMessage(nextClipboardViewer, m.Msg, m.WParam, m.LParam);
                    break;

                case WM_CHANGECBCHAIN:
                    if (m.WParam == nextClipboardViewer)
                        nextClipboardViewer = m.LParam;
                    else
                        SendMessage(nextClipboardViewer, m.Msg, m.WParam, m.LParam);
                    break;

                default:
                    base.WndProc(ref m);
                    break;
            }
        }

        static readonly string[] formats = Enum.GetNames(typeof(ClipboardFormat));

        private void ClipChanged()
        {
            IDataObject iData = Clipboard.GetDataObject();

            ClipboardFormat? format = null;

            foreach (var f in formats)
            {
                if (iData.GetDataPresent(f))
                {
                    format = (ClipboardFormat)Enum.Parse(typeof(ClipboardFormat), f);
                    break;
                }
            }

            object data = iData.GetData(format.ToString());

            if (data == null || format == null)
                return;

            if (OnClipboardChange != null)
                OnClipboardChange((ClipboardFormat)format, data);
        }


    }
}

public enum ClipboardFormat : byte
{
    /// <summary>Specifies the standard ANSI text format. This static field is read-only.
    /// </summary>
    /// <filterpriority>1</filterpriority>
    Text,
    /// <summary>Specifies the standard Windows Unicode text format. This static field
    /// is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    UnicodeText,
    /// <summary>Specifies the Windows device-independent bitmap (DIB) format. This static
    /// field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    Dib,
    /// <summary>Specifies a Windows bitmap format. This static field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    Bitmap,
    /// <summary>Specifies the Windows enhanced metafile format. This static field is
    /// read-only.</summary>
    /// <filterpriority>1</filterpriority>
    EnhancedMetafile,
    /// <summary>Specifies the Windows metafile format, which Windows Forms does not
    /// directly use. This static field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    MetafilePict,
    /// <summary>Specifies the Windows symbolic link format, which Windows Forms does
    /// not directly use. This static field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    SymbolicLink,
    /// <summary>Specifies the Windows Data Interchange Format (DIF), which Windows Forms
    /// does not directly use. This static field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    Dif,
    /// <summary>Specifies the Tagged Image File Format (TIFF), which Windows Forms does
    /// not directly use. This static field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    Tiff,
    /// <summary>Specifies the standard Windows original equipment manufacturer (OEM)
    /// text format. This static field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    OemText,
    /// <summary>Specifies the Windows palette format. This static field is read-only.
    /// </summary>
    /// <filterpriority>1</filterpriority>
    Palette,
    /// <summary>Specifies the Windows pen data format, which consists of pen strokes
    /// for handwriting software, Windows Forms does not use this format. This static
    /// field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    PenData,
    /// <summary>Specifies the Resource Interchange File Format (RIFF) audio format,
    /// which Windows Forms does not directly use. This static field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    Riff,
    /// <summary>Specifies the wave audio format, which Windows Forms does not directly
    /// use. This static field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    WaveAudio,
    /// <summary>Specifies the Windows file drop format, which Windows Forms does not
    /// directly use. This static field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    FileDrop,
    /// <summary>Specifies the Windows culture format, which Windows Forms does not directly
    /// use. This static field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    Locale,
    /// <summary>Specifies text consisting of HTML data. This static field is read-only.
    /// </summary>
    /// <filterpriority>1</filterpriority>
    Html,
    /// <summary>Specifies text consisting of Rich Text Format (RTF) data. This static
    /// field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    Rtf,
    /// <summary>Specifies a comma-separated value (CSV) format, which is a common interchange
    /// format used by spreadsheets. This format is not used directly by Windows Forms.
    /// This static field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    CommaSeparatedValue,
    /// <summary>Specifies the Windows Forms string class format, which Windows Forms
    /// uses to store string objects. This static field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    StringFormat,
    /// <summary>Specifies a format that encapsulates any type of Windows Forms object.
    /// This static field is read-only.</summary>
    /// <filterpriority>1</filterpriority>
    Serializable,
}

I know it might be to much but but after wrapping it it should look like:

And then you use the class as:

    static void Main(string[] args)
    {

        ClipboardMonitor.Start();

        ClipboardMonitor.OnClipboardChange += new ClipboardMonitor.OnClipboardChangeEventHandler(ClipboardMonitor_OnClipboardChange);

        Console.Read();

        ClipboardMonitor.Stop(); // do not forget to stop



    }

    static void ClipboardMonitor_OnClipboardChange(ClipboardFormat format, object data)
    {
        Console.WriteLine("Clipboard changed and it has the format: "+format.ToString());
    }

Answer 2

However, between these two operations, it is possible for another operation to change the content of the clipboard.

When an application calls OpenClipboard(), no other application can use the clipboard. Once the application that has locked the clipboard calls CloseClipboard(), then any application can then use and lock the clipboard.

Is there a way to be notified when any application modifies the clipboard?

Yes. See the API SetClipboardViewer() and the messages WM_DRAWCLIPBOARD and WM_CHANGECBCHAIN.

More info here: http://msdn.microsoft.com/en-us/library/ms649016(v=vs.85).aspx#_win32_Adding_a_Window_to_the_Clipboard_Viewer_Chain

Answer 3

All I could find was a Clipboard Monitor written in C#/VB.NET. I see WPF and WinForms, so I assume this is a viable options.

Involves pinvoking some methods from the user32 dll.

EDIT

At the time of edit, the original link above is broken. Here's an archive.org snapshot

Answer 4

Here is a write-up that I did a few years ago, detailing clipboard even monitoring via the Windows API: http://www.clipboardextender.com/developing-clipboard-aware-programs-for-windows/6 Please pay particular attention to the "common mistakes" section. Hardly anyone does this correctly the first time.