Html to Pdf 的另類解決方案

Background

項目里要求將一個HTML頁面(支付結果)生成pdf文檔。頁面有圖片，有表格，貌似開源的iTextSharp應付不了.

在一番搜索之后，找到了wkhtmltopdf,一個命令行的開源轉換工具，支持指定url或本地html file的路徑，試用后效果不錯，還特意用wkhtmltopdf寫了一個工具將博客園的帖子備份pdf到本地，后續有空把這個工具分享出來

But,發給客戶測試兩天運行效果不太理想，出現一些未知錯誤，而且奇怪的是在測試環境沒問題，正式環境卻頻繁出錯。最后客戶放棄這個方案
附上 WkhtmlToXSharp C# wrapper wrapper (using P/Invoke) for the excelent Html to PDF conversion library wkhtmltopdf library.

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OK，來到正題，另類的解決方案：Hook

調用IE打印功能，使用XPS打印機，先將HTML文件生成xps文檔，再生成pdf

新建WinForm 項目，拖入WebBrowser控件，代碼指定Url到本地html文件路徑，等待文檔加載完成后 WebBrowser.Print(); OK，運行，會彈出選擇打印機的對話框，如圖一。點擊打印后，彈出另存為的對話框，輸入xps路徑后保存(圖二)，即可得到一份xps文檔。

圖一:選擇打印機

圖二:輸入xps路徑

從上面可以看到，這里的打印需要與UI交互，人工點擊打印，輸入xps路徑保存才行。
接下來在網絡搜索:怎么不顯示對話框，直接打印生成xps文件，在stackoverflow,codeproject看了很多，沒找到辦法。后來偶然翻到園子前人的文章，采用hook方式，UI Automation來完成打印和保存的動作，覺得這個方案可行

接下來上代碼吧

	//調用WebBrowser.Print的代碼就忽略了，直接看鈎子
	IntPtr hwndDialog;
    string pathFile;
    EnumBrowserFileSaveType saveType;

    // Imports of the User32 DLL. 
    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    public static extern IntPtr SendMessage(IntPtr hWnd, int msg, int wParam, int lParam);

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    public static extern IntPtr GetDlgItem(IntPtr hWnd, int nIDDlgItem);

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    static extern private bool SetWindowText(IntPtr hWnd, string lpString);
    [DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool IsWindowVisible(IntPtr hWnd);

    //Win32 Api定義
    [DllImport("user32.dll")]
    static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

    [DllImport("user32.dll")]
    static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfeter, string lpszClass, string lpszWindow);

    [DllImport("user32.dll")]
    static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, String lParam);

    [DllImport("user32.dll")]
    static extern bool PostMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);


    //Win32消息定義
    const uint WM_SETTEXT = 0x000c;
    const uint WM_IME_KEYDOWN = 0x0290;
    const uint WM_LBUTTONDOWN = 0x0201;
    const uint WM_LBUTTONUP = 0x0202;

    // The thread procedure performs the message loop and place the data
    public void ThreadProc()
    {
        int maxRetry = 10;
        int retry = 0;
        IntPtr hWndPrint = FindWindow("#32770", "打印");
        IntPtr hWnd = FindWindow("#32770", "文件另存為");
        if (hWnd != IntPtr.Zero)
        {
            log.InfoFormat("got saveas dialog handle. Printer Dialog skipped.");
        }
        else
        {
            Thread.Sleep(200);
            hWndPrint = FindWindow("#32770", "打印");

            //這里有時候獲取不到window,所以加了Sleep，多試幾次
            while (hWndPrint == IntPtr.Zero && retry < maxRetry)
            {
                Thread.Sleep(200);
                log.InfoFormat("retry get Print dialog handle.retry:{0}", retry);
                hWndPrint = FindWindow("#32770", "打印");
                retry++;
            }
            if (hWndPrint == IntPtr.Zero)
            {
                //wait 1 second,retry again
                Thread.Sleep(1000);
                hWndPrint = FindWindow("#32770", "打印");
            }
            if (hWndPrint == IntPtr.Zero)
            {
                log.InfoFormat("Did not get Print dialog handle.retry:{0}", retry);
                return;
            }
            log.InfoFormat("got Print dialog handle.retry:{0}", retry);
            //select printer dialog
            IntPtr hChildP;
            hChildP = IntPtr.Zero;
            hChildP = FindWindowEx(hWndPrint, IntPtr.Zero, "Button", "打印(&P)");
            // 向保存按鈕發送2個消息，以模擬click消息，借此來按下保存按鈕
            PostMessage(hChildP, WM_LBUTTONDOWN, IntPtr.Zero, IntPtr.Zero);
            PostMessage(hChildP, WM_LBUTTONUP, IntPtr.Zero, IntPtr.Zero);
            Application.DoEvents();
        }

        //hWnd = FindWindow("#32770", null);
        hWnd = FindWindow("#32770", "文件另存為");
        //To avoid race condition, we are forcing this thread to wait until Saveas dialog is displayed.
        retry = 0;
        while ((!IsWindowVisible(hWnd) || hWnd == IntPtr.Zero) && retry < maxRetry)
        {
            Thread.Sleep(200);
            log.InfoFormat("retry get saveas dialog handle.retry:{0}", retry);
            hWnd = FindWindow("#32770", null);
            retry++;
            Application.DoEvents();
        }
        log.InfoFormat("got saveas dialog handle.retry:{0}", retry);
        if (hWnd == IntPtr.Zero)
        {
            //wait 1 second,retry again
            Thread.Sleep(1000);
            hWnd = FindWindow("#32770", "文件另存為");
        }
        if (hWnd == IntPtr.Zero)
        {
            return;
        }
        Application.DoEvents();

        IntPtr hChild;
        // 由於輸入框被多個控件嵌套，因此需要一級一級的往控件內找到輸入框
        hChild = FindWindowEx(hWnd, IntPtr.Zero, "DUIViewWndClassName", String.Empty);
        hChild = FindWindowEx(hChild, IntPtr.Zero, "DirectUIHWND", String.Empty);
        hChild = FindWindowEx(hChild, IntPtr.Zero, "FloatNotifySink", String.Empty);
        hChild = FindWindowEx(hChild, IntPtr.Zero, "ComboBox", String.Empty);
        hChild = FindWindowEx(hChild, IntPtr.Zero, "Edit", String.Empty); // File name edit control
        // 向輸入框發送消息，填充目標xps文件名
        SendMessage(hChild, WM_SETTEXT, IntPtr.Zero, pathFile);
        // 等待1秒鍾
        System.Threading.Thread.Sleep(1000);
        // 找到對話框內的保存按鈕
        hChild = IntPtr.Zero;
        hChild = FindWindowEx(hWnd, IntPtr.Zero, "Button", "保存(&S)");
        // 向保存按鈕發送2個消息，以模擬click消息，借此來按下保存按鈕
        PostMessage(hChild, WM_LBUTTONDOWN, IntPtr.Zero, IntPtr.Zero);
        PostMessage(hChild, WM_LBUTTONUP, IntPtr.Zero, IntPtr.Zero);

        // Clean up GUI - we have clicked save button.
        //GC is going to do that cleanup job, so we are OK
        Application.DoEvents();
        //Terminate the thread.
        return;
    }

接下來有關xps轉pdf，使用了Spire.Pdf,官方有demo，這里不再說明

有圖有真相

有關自動選擇XPS Document Writer的hook代碼我還沒完成，各位賜教！