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copied!<p>I believe one of the earlier solutions doesn't check for a null on the dispose method:</p> <pre><code>using System; using System.ComponentModel; using System.Runtime.InteropServices; using System.Windows.Forms; using System.Drawing; namespace ClipboardAssist { // Must inherit Control, not Component, in order to have Handle [DefaultEvent("ClipboardChanged")] public partial class ClipboardMonitor : Control { IntPtr nextClipboardViewer; public ClipboardMonitor() { this.BackColor = Color.Red; this.Visible = false; nextClipboardViewer = (IntPtr)SetClipboardViewer((int)this.Handle); } /// <summary> /// Clipboard contents changed. /// </summary> public event EventHandler<ClipboardChangedEventArgs> ClipboardChanged; protected override void Dispose(bool disposing) { if(nextClipboardViewer != null) ChangeClipboardChain(this.Handle, nextClipboardViewer); } [DllImport("User32.dll")] protected static extern int SetClipboardViewer(int 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); protected override void WndProc(ref System.Windows.Forms.Message m) { // defined in winuser.h const int WM_DRAWCLIPBOARD = 0x308; const int WM_CHANGECBCHAIN = 0x030D; switch (m.Msg) { case WM_DRAWCLIPBOARD: OnClipboardChanged(); 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; } } void OnClipboardChanged() { try { IDataObject iData = Clipboard.GetDataObject(); if (ClipboardChanged != null) { ClipboardChanged(this, new ClipboardChangedEventArgs(iData)); } } catch (Exception e) { // Swallow or pop-up, not sure // Trace.Write(e.ToString()); MessageBox.Show(e.ToString()); } } } public class ClipboardChangedEventArgs : EventArgs { public readonly IDataObject DataObject; public ClipboardChangedEventArgs(IDataObject dataObject) { DataObject = dataObject; } } } </code></pre>

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