重复下载不可靠吗？

Question

WatiN 似乎不能一致地处理重复的下载对话框：

        foreach (string file in lstFiles)
        {
            // continue if no download link
            if (!ie.Element([search criteria]).Exists) continue;

            var btnDownload = ie.Element([search criteria]);
            string fullFilename = workingDir + "\\" + file;
            FileDownloadHandler download = new FileDownloadHandler(fullFilename);
            using (new UseDialogOnce(ie.DialogWatcher, download))
            {
                btnDownload.ClickNoWait();

                download.WaitUntilFileDownloadDialogIsHandled(30);
                download.WaitUntilDownloadCompleted(150);
                ie.RemoveDialogHandler(download);
            }
        }

基本上，我循环浏览我期望可用的文件名列表，然后单击下载按钮。这通常有效，但是经过多次下载（情况各不相同，有时所有可用的下载，有时什么都没有），它会在等待处理对话框时挂起。该按钮被正确识别，下载对话框出现，只是没有被检测和处理。它不是特定于站点的，因为其他站点上的类似方法也取得了不同程度的成功。有人以前遇到过这个问题并知道解决方法吗？

编辑：重复下载在 Server 2008 中不起作用。在 Win7 中，这种情况在一次或多次成功重复下载后随机发生。

Answer 1

出现此问题的原因是 IE 文件下载对话框由 2 个窗口组成。 WatiN DialogWatcher 获取所有系统窗口并尝试在 foreach 循环中处理它们。处理第一个正确的对话框窗口后，DialogWatcher 获取下一个具有相同属性并且是有效下载对话框的窗口。 DialogWatcher 开始等待，直到该窗口可见，但在处理前一个窗口后立即关闭。
我的解决方案是在处理任何对话框后从 foreach 循环返回：

    #region WatiN Copyright (C) 2006-2011 Jeroen van Menen

//Copyright 2006-2011 Jeroen van Menen
//
//   Licensed under the Apache License, Version 2.0 (the "License");
//   you may not use this file except in compliance with the License.
//   You may obtain a copy of the License at
//
//       http://www.apache.org/licenses/LICENSE-2.0
//
//   Unless required by applicable law or agreed to in writing, software
//   distributed under the License is distributed on an "AS IS" BASIS,
//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//   See the License for the specific language governing permissions and
//   limitations under the License.

#endregion Copyright

using System;
using System.Collections.Generic;
using System.Threading;
using WatiN.Core.Exceptions;
using WatiN.Core.Interfaces;
using WatiN.Core.Logging;
using WatiN.Core.Native.InternetExplorer;
using WatiN.Core.Native.Windows;
using WatiN.Core.UtilityClasses;

namespace WatiN.Core.DialogHandlers
{
    /// <summary>
    /// This class handles alert/popup dialogs. Every second it checks if a dialog
    /// is shown. If so, it stores it's message in the alertQueue and closses the dialog
    /// by clicking the close button in the title bar.  
    /// </summary>
    public class DialogWatcher : IDisposable
    {
        private static IList<DialogWatcher> dialogWatchers = new List<DialogWatcher>();

        private bool _keepRunning = true;
        private readonly IList<IDialogHandler> _handlers;
        private readonly Thread _watcherThread;
        private bool _closeUnhandledDialogs = Settings.AutoCloseDialogs;

        public Window MainWindow { get; private set; }


        /// <summary>
        /// Gets the dialog watcher for the specified (main) internet explorer window. 
        /// It creates new instance if no dialog watcher for the specified window exists.
        /// </summary>
        /// <param name="mainWindowHwnd">The (main) internet explorer window.</param>
        /// <returns></returns>
        public static DialogWatcher GetDialogWatcher(IntPtr mainWindowHwnd)
        {
            var window = new Window(mainWindowHwnd);
            Logger.LogDebug("GetDialogWatcher mainhwnd: " + window.Hwnd + ", " + window.Title);

            var toplevelWindow = window.ToplevelWindow;
            Logger.LogDebug("GetDialogWatcher mainhwnd: " + toplevelWindow.Hwnd + ", " + toplevelWindow.Title);

            CleanupDialogWatcherCache();

            var dialogWatcher = GetDialogWatcherFromCache(toplevelWindow);

            // If no dialogwatcher exists for the ieprocessid then 
            // create a new one, store it and return it.
            if (dialogWatcher == null)
            {
                dialogWatcher = new DialogWatcher(toplevelWindow);

                dialogWatchers.Add(dialogWatcher);
            }

            return dialogWatcher;
        }

        public static DialogWatcher GetDialogWatcherFromCache(Window mainWindow)
        {
            // Loop through already created dialogwatchers and
            // return a dialogWatcher if one exists for the given processid
            foreach (var dialogWatcher in dialogWatchers)
            {
                if (dialogWatcher.MainWindow.Equals(mainWindow))
                {
                    return dialogWatcher;
                }
            }

            return null;
        }

        public static void CleanupDialogWatcherCache()
        {
            var cleanedupDialogWatcherCache = new List<DialogWatcher>();

            foreach (var dialogWatcher in dialogWatchers)
            {
                if (!dialogWatcher.IsRunning)
                {
                    dialogWatcher.Dispose();
                }
                else
                {
                    cleanedupDialogWatcherCache.Add(dialogWatcher);
                }
            }

            dialogWatchers = cleanedupDialogWatcherCache;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="DialogWatcher"/> class.
        /// You are encouraged to use the Factory method <see cref="DialogWatcher.GetDialogWatcherFromCache"/>
        /// instead.
        /// </summary>
        /// <param name="mainWindow">The main window handle of internet explorer.</param>
        public DialogWatcher(Window mainWindow)
        {
            MainWindow = mainWindow;

            _handlers = new List<IDialogHandler>();

            // Create thread to watch windows
            _watcherThread = new Thread(Start);
            // Start the thread.
            _watcherThread.Start();
        }

        /// <summary>
        /// Increases the reference count of this DialogWatcher instance with 1.
        /// </summary>
        public void IncreaseReferenceCount()
        {
            ReferenceCount++;
        }

        /// <summary>
        /// Decreases the reference count of this DialogWatcher instance with 1.
        /// When reference count becomes zero, the Dispose method will be 
        /// automatically called. This method will throw an <see cref="ReferenceCountException"/>
        /// if the reference count is zero.
        /// </summary>
        public void DecreaseReferenceCount()
        {
            if (ReferenceCount > 0)
            {
                ReferenceCount--;
            }
            else
            {
                throw new ReferenceCountException();
            }

            if (ReferenceCount == 0)
            {
                Dispose();
            }
        }

        /// <summary>
        /// Adds the specified handler.
        /// </summary>
        /// <param name="handler">The handler.</param>
        public void Add(IDialogHandler handler)
        {
            lock (this)
            {
                _handlers.Add(handler);
            }
        }

        /// <summary>
        /// Removes the specified handler.
        /// </summary>
        /// <param name="handler">The handler.</param>
        public void Remove(IDialogHandler handler)
        {
            lock (this)
            {
                _handlers.Remove(handler);
            }
        }

        /// <summary>
        /// Removes all instances that match <paramref name="handler"/>.
        /// This method determines equality by calling Object.Equals.
        /// </summary>
        /// <param name="handler">The object implementing IDialogHandler.</param>
        /// <example>
        /// If you want to use RemoveAll with your custom dialog handler to
        /// remove all instances of your dialog handler from a DialogWatcher instance,
        /// you should override the Equals method in your custom dialog handler class 
        /// like this:
        /// <code>
        /// public override bool Equals(object obj)
        /// {
        ///   if (obj == null) return false;
        ///   
        ///   return (obj is YourDialogHandlerClassNameGoesHere);
        /// }                               
        /// </code>
        /// You could also inherit from <see cref="BaseDialogHandler"/> instead of implementing
        /// <see cref="IDialogHandler"/> in your custom dialog handler. <see cref="BaseDialogHandler"/> provides
        /// overrides for Equals and GetHashCode that work with RemoveAll.
        /// </example>
        public void RemoveAll(IDialogHandler handler)
        {
            while (Contains(handler))
            {
                Remove(handler);
            }
        }

        /// <summary>
        /// Removes all registered dialog handlers.
        /// </summary>
        public void Clear()
        {
            lock (this)
            {
                _handlers.Clear();
            }
        }

        /// <summary>
        /// Determines whether this <see cref="DialogWatcher"/> contains the specified dialog handler.
        /// </summary>
        /// <param name="handler">The dialog handler.</param>
        /// <returns>
        ///     <c>true</c> if [contains] [the specified handler]; otherwise, <c>false</c>.
        /// </returns>
        public bool Contains(IDialogHandler handler)
        {
            lock (this)
            {
                return _handlers.Contains(handler);
            }
        }

        /// <summary>
        /// Gets the count of registered dialog handlers.
        /// </summary>
        /// <value>The count.</value>
        public int Count
        {
            get
            {
                lock (this)
                {
                    return _handlers.Count;
                }
            }
        }

        /// <summary>
        /// Gets or sets a value indicating whether unhandled dialogs should be closed automaticaly.
        /// The initial value is set to the value of <cref name="Settings.AutoCloseDialogs" />.
        /// </summary>
        /// <value>
        ///     <c>true</c> if unhandled dialogs should be closed automaticaly; otherwise, <c>false</c>.
        /// </value>
        public bool CloseUnhandledDialogs
        {
            get
            {
                lock (this)
                {
                    return _closeUnhandledDialogs;
                }
            }
            set
            {
                lock (this)
                {
                    _closeUnhandledDialogs = value;
                }
            }
        }

        /// <summary>
        /// Gets the (main) internet explorer window handle this dialog watcher watches.
        /// </summary>
        /// <value>The process id.</value>
        public IntPtr MainWindowHwnd
        {
            get { return MainWindow.Hwnd; }
        }

        /// <summary>
        /// Called by the constructor to start watching popups
        /// on a separate thread.
        /// </summary>
        private void Start()
        {
            while (_keepRunning)
            {
                if (MainWindow.Exists())
                {
                    var winEnumerator = new WindowsEnumerator();
                    var windows = winEnumerator.GetWindows(win => true);

                    foreach (var window in windows)
                    {
                        if (!_keepRunning) return;
                        if(HandleWindow(window))
                            break;
                    }

                    // Keep DialogWatcher responsive during 1 second sleep period
                    var count = 0;
                    while (_keepRunning && count < 5)
                    {
                        Thread.Sleep(200);
                        count++;
                    }
                }
                else
                {
                    _keepRunning = false;
                }

            }
        }

        public bool IsRunning
        {
            get { return _watcherThread.IsAlive; }
        }

        public int ReferenceCount { get; private set; }

        /// <summary>
        /// Get the last stored exception thrown by a dialog handler while 
        /// calling the <see cref="IDialogHandler.HandleDialog"/> method of the
        /// dialog handler.
        /// </summary>
        /// <value>The last exception.</value>
        public Exception LastException { get; private set; }

        /// <summary>
        /// If the window is a dialog and visible, it will be passed to
        /// the registered dialog handlers. I none if these can handle
        /// it, it will be closed if <see cref="CloseUnhandledDialogs"/>
        /// is <c>true</c>.
        /// </summary>
        /// <param name="window">The window.</param>
        /// <returns>
        /// <c>true</c> if dialog is handled by one of handlers; otherwise, <c>false</c>.
        /// </returns>
        public bool HandleWindow(Window window)
        {
            if (!window.IsDialog()) return false;
            if (!HasDialogSameProcessNameAsBrowserWindow(window)) return false;

            // This is needed otherwise the window Style will return a "wrong" result.
            WaitUntilVisibleOrTimeOut(window);

            // Lock the thread and see if a handler will handle
            // this dialog window
            lock (this)
            {
                foreach (var dialogHandler in _handlers)
                {
                    try
                    {
                        if (dialogHandler.CanHandleDialog(window, MainWindow.Hwnd))
                        {
                            if (dialogHandler.HandleDialog(window)) return true;
                        }
                    }
                    catch (Exception e)
                    {
                        LastException = e;

                        Logger.LogAction((LogFunction log) => { log("Exception was thrown while DialogWatcher called HandleDialog: {0}",e.ToString()); });
                    }
                }

                // If no handler handled the dialog, see if the dialog
                // should be closed automatically.
                if (!CloseUnhandledDialogs || !MainWindow.Equals(window.ToplevelWindow)) return false;

                Logger.LogAction((LogFunction log) => { log("Auto closing dialog with title: '{0}', text: {1}, style: ", window.Title, window.Message, window.StyleInHex); });
                window.ForceClose();
            }
            return false;
        }

        private bool HasDialogSameProcessNameAsBrowserWindow(Window window)
        {
            var comparer = new Comparers.StringComparer(window.ProcessName, true);
            return comparer.Compare(MainWindow.ProcessName);
        }

        private static void WaitUntilVisibleOrTimeOut(Window window)
        {
            // Wait untill window is visible so all properties
            // of the window class (like Style and StyleInHex)
            // will return valid values.
            var tryActionUntilTimeOut = new TryFuncUntilTimeOut(TimeSpan.FromSeconds(Settings.WaitForCompleteTimeOut));
            var success = tryActionUntilTimeOut.Try(() => window.Visible);

            if (!success)
            {
                Logger.LogAction((LogFunction log) => { log("Dialog with title '{0}' not visible after {1} seconds.", window.Title, Settings.WaitForCompleteTimeOut); });
            }
        }

        #region IDisposable Members

        /// <summary>
        /// Performs application-defined tasks associated with freeing, releasing, or
        /// resetting unmanaged resources.
        /// </summary>
        public void Dispose()
        {
            lock (this)
            {
                _keepRunning = false;
            }
            if (IsRunning)
            {
                _watcherThread.Join();
            }
            Clear();
        }

        #endregion
    }
}

Answer 2

我的团队在使用 WatiN 自动化 IE8 时也遇到了这个问题。问题似乎与 IE 相关，可能需要进行一些耗时的清理工作。我们最终使用的解决方法是在外部循环中调用 IE 的 new 实例，每次迭代都会处理它，然后等待 5 秒以解决后台发生的任何问题。这是一次黑客攻击，但完成了工作。

foreach (var file in lstFiles)
{
    string fullFilename = workingDir + "\\" + file;
    using (var browser = new IE(fullFilename))
    {
        //page manipulations...

        FileDownloadHandler download = new FileDownloadHandler(fullFilename);
        using (new UseDialogOnce(browser.DialogWatcher, download))
        { //lnkFile.ClickNoWait(); 
            download.WaitUntilFileDownloadDialogIsHandled(15);
            download.WaitUntilDownloadCompleted(150);
        }
    }
    Thread.Sleep(5000);
}