网络浏览器行为问题

Question

我正在尝试使用 .NET C# 自动化 Web 浏览器。问题是控件或者我应该说 IE 浏览器在不同的计算机上表现得很奇怪。例如，我在第一台计算机上单击链接并填写 Ajax 弹出表单，没有任何错误：

private void btn_Start_Click(object sender, RoutedEventArgs e)
{
    webbrowserIE.Navigate("http://www.test.com/");
    webbrowserIE.DocumentCompleted += fillup_LoadCompleted; 
}

void fillup_LoadCompleted(object sender, System.Windows.Forms.WebBrowserDocumentCompletedEventArgs e)
{
    System.Windows.Forms.HtmlElement ele = web_BrowserIE.Document.GetElementById("login");
    if (ele != null)
        ele.InvokeMember("Click");

    if (this.web_BrowserIE.ReadyState == System.Windows.Forms.WebBrowserReadyState.Complete)
    {
        web_BrowserIE.Document.GetElementById("login").SetAttribute("value", myUserName);
        web_BrowserIE.Document.GetElementById("password").SetAttribute("value", myPassword);

        foreach (System.Windows.Forms.HtmlElement el in web_BrowserIE.Document.GetElementsByTagName("button"))
        {
            if (el.InnerText == "Login")
            {
                el.InvokeMember("click");
            }
        }

        web_BrowserIE.DocumentCompleted -= fillup_LoadCompleted;        
    }
}

但是，上面的代码不能在第二台电脑上运行，唯一的点击方式是这样的：

private void btn_Start_Click(object sender, RoutedEventArgs e)
{
    webbrowserIE.DocumentCompleted += click_LoadCompleted;
    webbrowserIE.Navigate("http://www.test.com/"); 
}

void click_LoadCompleted(object sender, System.Windows.Forms.WebBrowserDocumentCompletedEventArgs e)
{
    if (this.webbrowserIE.ReadyState == System.Windows.Forms.WebBrowserReadyState.Complete)
    {
        System.Windows.Forms.HtmlElement ele = webbrowserIE.Document.GetElementById("login");
        if (ele != null)
            ele.InvokeMember("Click");

        webbrowserIE.DocumentCompleted -= click_LoadCompleted;
        webbrowserIE.DocumentCompleted += fillup_LoadCompleted;
    }
}

void click_LoadCompleted(object sender, System.Windows.Forms.WebBrowserDocumentCompletedEventArgs e)
{

        webbrowserIE.Document.GetElementById("login_login").SetAttribute("value", myUserName);
        webbrowserIE.Document.GetElementById("login_password").SetAttribute("value", myPassword);

        //If you know the ID of the form you would like to submit:
        foreach (System.Windows.Forms.HtmlElement el in webbrowserIE.Document.GetElementsByTagName("button"))
        {
            if (el.InnerText == "Login")
            {
                el.InvokeMember("click");
            }
        }

        webbrowserIE.DocumentCompleted -= click_LoadCompleted;      
}

因此，在第二个解决方案中，我必须调用两个加载完成链。有人可以建议我应该如何处理这个问题吗？此外，提出更稳健的方法的建议将非常有帮助。提前谢谢你

Answer 1

我可以推荐两件事：

• 不要在 DocumentComplete 事件上执行您的代码，而是在 DOM window.onload 事件上执行。
• 为确保您的网页在 WebBrowser 控件中的行为与在完整 Internet Explorer 浏览器中的行为方式相同，请考虑实现 Feature Control。

[EDITED] 根据您的代码结构，还有一个建议。显然，您执行了一系列导航/处理DocumentComplete 操作。为此，使用async/await 可能更自然、更容易。这是一个这样做的例子，有或没有async/await。它也说明了如何处理onload：

async Task DoNavigationAsync()
{
    bool documentComplete = false;
    TaskCompletionSource<bool> onloadTcs = null;

    WebBrowserDocumentCompletedEventHandler handler = delegate 
    {
        if (documentComplete)
            return; // attach to onload only once per each Document
        documentComplete = true;

        // now subscribe to DOM onload event
        this.wb.Document.Window.AttachEventHandler("onload", delegate
        {
            // each navigation has its own TaskCompletionSource
            if (onloadTcs.Task.IsCompleted)
                return; // this should not be happening

            // signal the completion of the page loading
            onloadTcs.SetResult(true);
        });
    };

    // register DocumentCompleted handler
    this.wb.DocumentCompleted += handler;

    // Navigate to http://www.example.com?i=1
    documentComplete = false;
    onloadTcs = new TaskCompletionSource<bool>();
    this.wb.Navigate("http://www.example.com?i=1");
    await onloadTcs.Task;
    // the document has been fully loaded, you can access DOM here
    MessageBox.Show(this.wb.Document.Url.ToString());

    // Navigate to http://example.com?i=2
    // could do the click() simulation instead

    documentComplete = false;
    onloadTcs = new TaskCompletionSource<bool>(); // new task for new navigation
    this.wb.Navigate("http://example.com?i=2");
    await onloadTcs.Task;
    // the document has been fully loaded, you can access DOM here
    MessageBox.Show(this.wb.Document.Url.ToString());

    // no more navigation, de-register DocumentCompleted handler
    this.wb.DocumentCompleted -= handler;
}

这是相同的代码没有async/await 模式（对于.NET 4.0）：

Task DoNavigationAsync()
{
    // save the correct continuation context for Task.ContinueWith
    var continueContext = TaskScheduler.FromCurrentSynchronizationContext(); 

    bool documentComplete = false;
    TaskCompletionSource<bool> onloadTcs = null;

    WebBrowserDocumentCompletedEventHandler handler = delegate 
    {
        if (documentComplete)
            return; // attach to onload only once per each Document
        documentComplete = true;

        // now subscribe to DOM onload event
        this.wb.Document.Window.AttachEventHandler("onload", delegate
        {
            // each navigation has its own TaskCompletionSource
            if (onloadTcs.Task.IsCompleted)
                return; // this should not be happening

            // signal the completion of the page loading
            onloadTcs.SetResult(true);
        });
    };

    // register DocumentCompleted handler
    this.wb.DocumentCompleted += handler;

    // Navigate to http://www.example.com?i=1
    documentComplete = false;
    onloadTcs = new TaskCompletionSource<bool>();
    this.wb.Navigate("http://www.example.com?i=1");

    return onloadTcs.Task.ContinueWith(delegate 
    {
        // the document has been fully loaded, you can access DOM here
        MessageBox.Show(this.wb.Document.Url.ToString());

        // Navigate to http://example.com?i=2
        // could do the 'click()' simulation instead

        documentComplete = false;
        onloadTcs = new TaskCompletionSource<bool>(); // new task for new navigation
        this.wb.Navigate("http://example.com?i=2");

        onloadTcs.Task.ContinueWith(delegate 
        {
            // the document has been fully loaded, you can access DOM here
            MessageBox.Show(this.wb.Document.Url.ToString());

            // no more navigation, de-register DocumentCompleted handler
            this.wb.DocumentCompleted -= handler;
        }, continueContext);

    }, continueContext);
}

注意，在这两种情况下，它仍然是一段异步代码，它返回一个Task 对象。以下是如何处理此类任务完成的示例：

private void Form1_Load(object sender, EventArgs e)
{
    DoNavigationAsync().ContinueWith(_ => {
        MessageBox.Show("Navigation complete!");
    }, TaskScheduler.FromCurrentSynchronizationContext());
}

在这里使用TAP pattern 的好处是DoNavigationAsync 是一个自包含的、独立的方法。它可以重复使用，并且不会干扰父对象（在本例中为主窗体）的状态。