A detailed introduction to the code for implementing Windows Clipboard Monitor in c#

Windows Clipboard

The Clipboard (ClipBoard) is an area in the memory. It is a very useful tool built into Windows. Through the small clipboard, A colorful bridge makes it possible to transfer and share information between various applications. However, the fly in the ointment is that the clipboard can only retain one copy of data, and whenever new data is passed in, the old ones will be overwritten.

Related Windows API

The most important one is SetClipboardViewer. Whenever the contents of the clipboard change, this function adds the window to be notified through the WM_DRAWCLIPBOARD message. window chain.
Since the handle to the next window in the clipboard viewer chain has not yet been returned, the application should not pass the WM_DRAWCLIPBOARD message it received during the SetClipboardViewer
call.
If you want to remove the window chain from the clipboard observer chain, the application must call the ChangeClipboard member function.

        #region Definitions
        //Constants for API Calls...
        private const int WM_DRAWCLIPBOARD = 0x308;
        private const int WM_CHANGECBCHAIN = 0x30D;

        //Handle for next clipboard viewer...
        private IntPtr mNextClipBoardViewerHWnd;

        //API declarations...
        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        static public extern IntPtr SetClipboardViewer(IntPtr hWndNewViewer);
        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        static public extern bool ChangeClipboardChain(IntPtr HWnd, IntPtr HWndNext);
        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        public static extern int SendMessage(IntPtr hWnd, int msg, int wParam, int lParam);
        #endregion

wndproc function

The operating system sends a series of messages to the application, such as left button down and left button up, and the application will pass GetMessage The other methods finally submit the message to the window process (WndProc [full name in English: windows process]), which points to a pointer to an application-defined window process.

We need to rewrite this function to handle the clipboard content change event:

        #region Message Process
        //Override WndProc to get messages...
        protected override void WndProc(ref Message m)
        {
            switch (m.Msg)
            {
                case WM_DRAWCLIPBOARD:
                    {
                        //The clipboard has changed...
                        //##########################################################################
                        // Process Clipboard Here :)........................
                        //##########################################################################
                        SendMessage(mNextClipBoardViewerHWnd, m.Msg, m.WParam.ToInt32(), m.LParam.ToInt32());

                        //显示剪贴板中的文本信息
                        if (Clipboard.ContainsText())
                        {
                            label1.Text = Clipboard.GetText();
                        }
                        //显示剪贴板中的图片信息
                        if (Clipboard.ContainsImage())
                        {
                            pictureBox1.Image = Clipboard.GetImage();
                            pictureBox1.Update();
                        }
                        break;
                    }
                case WM_CHANGECBCHAIN:
                    {
                        //Another clipboard viewer has removed itself...
                        if (m.WParam == (IntPtr)mNextClipBoardViewerHWnd)
                        {
                            mNextClipBoardViewerHWnd = m.LParam;
                        }
                        else
                        {
                            SendMessage(mNextClipBoardViewerHWnd, m.Msg, m.WParam.ToInt32(), m.LParam.ToInt32());
                        }
                        break;
                    }
            }
            base.WndProc(ref m);
        }
        #endregion

Effect:

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