问题
This has been awnsered many times here and at other sites and its working, but I would like ideas to other ways to:
get the ReadyState = Complete after using a navigate or post, without using DoEvents because of all of its cons.
I would also note that using the DocumentComplete event woud not help here as I wont be navigating on only one page, but one after another like this.
wb.navigate("www.microsoft.com")
//dont use DoEvents loop here
wb.Document.Body.SetAttribute(textbox1, "login")
//dont use DoEvents loop here
if (wb.documenttext.contais("text"))
//do something
The way it is today its working by using DoEvents. I would like to know if anyone have a proper way to wait the async call of the browser methods to only then proceed with the rest of the logic. Just for the sake of it.
Thanks in advance.
回答1:
Below is a basic WinForms app code, illustrating how to wait for the DocumentCompleted event asynchronously, using async/await. It navigates to multiple pages, one after another. Everything is taking place on the main UI thread.
Instead of calling this.webBrowser.Navigate(url), it might be simulating a form button click, to trigger a POST-style navigation.
The webBrowser.IsBusy async loop logic is optional, its purpose is to account (non-deterministically) for the page's dynamic AJAX code which may take place after window.onload event.
using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace WebBrowserApp
{
public partial class MainForm : Form
{
WebBrowser webBrowser;
public MainForm()
{
InitializeComponent();
// create a WebBrowser
this.webBrowser = new WebBrowser();
this.webBrowser.Dock = DockStyle.Fill;
this.Controls.Add(this.webBrowser);
this.Load += MainForm_Load;
}
// Form Load event handler
async void MainForm_Load(object sender, EventArgs e)
{
// cancel the whole operation in 30 sec
var cts = new CancellationTokenSource(30000);
var urls = new String[] {
"http://www.example.com",
"http://www.gnu.org",
"http://www.debian.org" };
await NavigateInLoopAsync(urls, cts.Token);
}
// navigate to each URL in a loop
async Task NavigateInLoopAsync(string[] urls, CancellationToken ct)
{
foreach (var url in urls)
{
ct.ThrowIfCancellationRequested();
var html = await NavigateAsync(ct, () =>
this.webBrowser.Navigate(url));
Debug.Print("url: {0}, html: \n{1}", url, html);
}
}
// asynchronous navigation
async Task<string> NavigateAsync(CancellationToken ct, Action startNavigation)
{
var onloadTcs = new TaskCompletionSource<bool>();
EventHandler onloadEventHandler = null;
WebBrowserDocumentCompletedEventHandler documentCompletedHandler = delegate
{
// DocumentCompleted may be called several time for the same page,
// if the page has frames
if (onloadEventHandler != null)
return;
// so, observe DOM onload event to make sure the document is fully loaded
onloadEventHandler = (s, e) =>
onloadTcs.TrySetResult(true);
this.webBrowser.Document.Window.AttachEventHandler("onload", onloadEventHandler);
};
this.webBrowser.DocumentCompleted += documentCompletedHandler;
try
{
using (ct.Register(() => onloadTcs.TrySetCanceled(), useSynchronizationContext: true))
{
startNavigation();
// wait for DOM onload event, throw if cancelled
await onloadTcs.Task;
}
}
finally
{
this.webBrowser.DocumentCompleted -= documentCompletedHandler;
if (onloadEventHandler != null)
this.webBrowser.Document.Window.DetachEventHandler("onload", onloadEventHandler);
}
// the page has fully loaded by now
// optional: let the page run its dynamic AJAX code,
// we might add another timeout for this loop
do { await Task.Delay(500, ct); }
while (this.webBrowser.IsBusy);
// return the page's HTML content
return this.webBrowser.Document.GetElementsByTagName("html")[0].OuterHtml;
}
}
}
If you're looking to do something similar from a console app, here is an example of that.
回答2:
Here is a "quick & dirty" solution. It's not 100% foolproof but it doesn't block UI thread and it should be satisfactory to prototype WebBrowser control Automation procedures:
private async void testButton_Click(object sender, EventArgs e)
{
await Task.Factory.StartNew(
() =>
{
stepTheWeb(() => wb.Navigate("www.yahoo.com"));
stepTheWeb(() => wb.Navigate("www.microsoft.com"));
stepTheWeb(() => wb.Navigate("asp.net"));
stepTheWeb(() => wb.Document.InvokeScript("eval", new[] { "$('p').css('background-color','yellow')" }));
bool testFlag = false;
stepTheWeb(() => testFlag = wb.DocumentText.Contains("Get Started"));
if (testFlag) { /* TODO */ }
// ...
}
);
}
private void stepTheWeb(Action task)
{
this.Invoke(new Action(task));
WebBrowserReadyState rs = WebBrowserReadyState.Interactive;
while (rs != WebBrowserReadyState.Complete)
{
this.Invoke(new Action(() => rs = wb.ReadyState));
System.Threading.Thread.Sleep(300);
}
}
Here is a bit more generic version of testButton_Click method:
private async void testButton_Click(object sender, EventArgs e)
{
var actions = new List<Action>()
{
() => wb.Navigate("www.yahoo.com"),
() => wb.Navigate("www.microsoft.com"),
() => wb.Navigate("asp.net"),
() => wb.Document.InvokeScript("eval", new[] { "$('p').css('background-color','yellow')" }),
() => {
bool testFlag = false;
testFlag = wb.DocumentText.Contains("Get Started");
if (testFlag) { /* TODO */ }
}
//...
};
await Task.Factory.StartNew(() => actions.ForEach((x)=> stepTheWeb (x)));
}
[Update]
I have adapted my "quick & dirty" sample by borrowing and sligthly refactoring @Noseratio's NavigateAsync method from this topic. New code version would automate/execute asynchronously in UI thread context not only navigation operations but also Javascript/AJAX calls - any "lamdas"/one automation step task implementation methods.
All and every code reviews/comments are very welcome. Especially, from @Noseratio. Together, we will make this world better ;)
public enum ActionTypeEnumeration
{
Navigation = 1,
Javascript = 2,
UIThreadDependent = 3,
UNDEFINED = 99
}
public class ActionDescriptor
{
public Action Action { get; set; }
public ActionTypeEnumeration ActionType { get; set; }
}
/// <summary>
/// Executes a set of WebBrowser control's Automation actions
/// </summary>
/// <remarks>
/// Test form shoudl ahve the following controls:
/// webBrowser1 - WebBrowser,
/// testbutton - Button,
/// testCheckBox - CheckBox,
/// totalHtmlLengthTextBox - TextBox
/// </remarks>
private async void testButton_Click(object sender, EventArgs e)
{
try
{
var cts = new CancellationTokenSource(60000);
var actions = new List<ActionDescriptor>()
{
new ActionDescriptor() { Action = ()=> wb.Navigate("www.yahoo.com"), ActionType = ActionTypeEnumeration.Navigation} ,
new ActionDescriptor() { Action = () => wb.Navigate("www.microsoft.com"), ActionType = ActionTypeEnumeration.Navigation} ,
new ActionDescriptor() { Action = () => wb.Navigate("asp.net"), ActionType = ActionTypeEnumeration.Navigation} ,
new ActionDescriptor() { Action = () => wb.Document.InvokeScript("eval", new[] { "$('p').css('background-color','yellow')" }), ActionType = ActionTypeEnumeration.Javascript},
new ActionDescriptor() { Action =
() => {
testCheckBox.Checked = wb.DocumentText.Contains("Get Started");
},
ActionType = ActionTypeEnumeration.UIThreadDependent}
//...
};
foreach (var action in actions)
{
string html = await ExecuteWebBrowserAutomationAction(cts.Token, action.Action, action.ActionType);
// count HTML web page stats - just for fun
int totalLength = 0;
Int32.TryParse(totalHtmlLengthTextBox.Text, out totalLength);
totalLength += !string.IsNullOrWhiteSpace(html) ? html.Length : 0;
totalHtmlLengthTextBox.Text = totalLength.ToString();
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message, "Error");
}
}
// asynchronous WebBroswer control Automation
async Task<string> ExecuteWebBrowserAutomationAction(
CancellationToken ct,
Action runWebBrowserAutomationAction,
ActionTypeEnumeration actionType = ActionTypeEnumeration.UNDEFINED)
{
var onloadTcs = new TaskCompletionSource<bool>();
EventHandler onloadEventHandler = null;
WebBrowserDocumentCompletedEventHandler documentCompletedHandler = delegate
{
// DocumentCompleted may be called several times for the same page,
// if the page has frames
if (onloadEventHandler != null)
return;
// so, observe DOM onload event to make sure the document is fully loaded
onloadEventHandler = (s, e) =>
onloadTcs.TrySetResult(true);
this.wb.Document.Window.AttachEventHandler("onload", onloadEventHandler);
};
this.wb.DocumentCompleted += documentCompletedHandler;
try
{
using (ct.Register(() => onloadTcs.TrySetCanceled(), useSynchronizationContext: true))
{
runWebBrowserAutomationAction();
if (actionType == ActionTypeEnumeration.Navigation)
{
// wait for DOM onload event, throw if cancelled
await onloadTcs.Task;
}
}
}
finally
{
this.wb.DocumentCompleted -= documentCompletedHandler;
if (onloadEventHandler != null)
this.wb.Document.Window.DetachEventHandler("onload", onloadEventHandler);
}
// the page has fully loaded by now
// optional: let the page run its dynamic AJAX code,
// we might add another timeout for this loop
do { await Task.Delay(500, ct); }
while (this.wb.IsBusy);
// return the page's HTML content
return this.wb.Document.GetElementsByTagName("html")[0].OuterHtml;
}
回答3:
The solution is simple:
// MAKE SURE ReadyState = Complete
while (WebBrowser1.ReadyState.ToString() != "Complete") {
Application.DoEvents();
}
// Move on to your sub-sequence code...
Dirty and quick.. I am a VBA guys, this logic has been working forever, just took me days and found none for C# but I just figured this out myself.
Following is my complete function, the objective is to obtain a segment of info from a webpage:
private int maxReloadAttempt = 3;
private int currentAttempt = 1;
private string GetCarrier(string webAddress)
{
WebBrowser WebBrowser_4MobileCarrier = new WebBrowser();
string innerHtml;
string strStartSearchFor = "subtitle block pull-left\">";
string strEndSearchFor = "<";
try
{
WebBrowser_4MobileCarrier.ScriptErrorsSuppressed = true;
WebBrowser_4MobileCarrier.Navigate(webAddress);
// MAKE SURE ReadyState = Complete
while (WebBrowser_4MobileCarrier.ReadyState.ToString() != "Complete") {
Application.DoEvents();
}
// LOAD HTML
innerHtml = WebBrowser_4MobileCarrier.Document.Body.InnerHtml;
// ATTEMPT (x3) TO EXTRACT CARRIER STRING
while (currentAttempt <= maxReloadAttempt) {
if (innerHtml.IndexOf(strStartSearchFor) >= 0)
{
currentAttempt = 1; // Reset attempt counter
return Sub_String(innerHtml, strStartSearchFor, strEndSearchFor, "0"); // Method: "Sub_String" is my custom function
}
else
{
currentAttempt += 1; // Increment attempt counter
GetCarrier(webAddress); // Recursive method call
} // End if
} // End while
} // End Try
catch //(Exception ex)
{
}
return "Unavailable";
}
来源：https://stackoverflow.com/questions/21140349/get-readystate-from-webbrowser-control-without-doevents