How to wait until WebBrowser is completely loaded in VB.NET?

I am using the W开发者_如何学JAVAebBrowser control in my VB.NET application to load a few URLs ( ~10-15) and save their HTML source in a text file. However, my code doesn't write the source of the current page rather the initial one because the it is triggered even before the page is loaded.

How can I wait until the page is completely loaded before calling any event?

I tried the following code but it doesn't work.

Do Until WebBrowser1.ReadyState = WebBrowserReadyState.Complete
   Application.DoEvents()
Loop

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Salvete! I needed, simply, a function I could call to make the code wait for the page to load before it continued. After scouring the web for answers, and fiddling around for several hours, I came up with this to solve for myself, the exact dilemma you present. I know I am late in the game with an answer, but I wish to post this for anyone else who comes along.

usage: just call WaitForPageLoad() just after a call to navigation:

whatbrowser.Navigate("http://www.google.com")
WaitForPageLoad()

another example we don't combine the navigate feature with the page load, because sometimes you need to wait for a load without also navigating, for example, you might need to wait for a page to load that was started with an invokemember event:

whatbrowser.Document.GetElementById("UserName").InnerText = whatusername
whatbrowser.Document.GetElementById("Password").InnerText = whatpassword
whatbrowser.Document.GetElementById("LoginButton").InvokeMember("click")
WaitForPageLoad()

Here is the code: You need both subs plus the accessible variable, pageready. First, make sure to fix the variable called whatbrowser to be your webbrowser control

Now, somewhere in your module or class, place this:

Private Property pageready As Boolean = False

#Region "Page Loading Functions"
    Private Sub WaitForPageLoad()
        AddHandler whatbrowser.DocumentCompleted, New WebBrowserDocumentCompletedEventHandler(AddressOf PageWaiter)
        While Not pageready
            Application.DoEvents()
        End While
        pageready = False
    End Sub

    Private Sub PageWaiter(ByVal sender As Object, ByVal e As WebBrowserDocumentCompletedEventArgs)
        If whatbrowser.ReadyState = WebBrowserReadyState.Complete Then
            pageready = True
            RemoveHandler whatbrowser.DocumentCompleted, New WebBrowserDocumentCompletedEventHandler(AddressOf PageWaiter)
        End If
    End Sub

#End Region

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Sounds like you want to catch the DocumentCompleted event of your webbrowser control.

MSDN has a couple of good articles about the webbrowser control - WebBrowser Class has lots of examples, and How to: Add Web Browser Capabilities to a Windows Forms Application

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Technically, there are two issues with the code posted by BGM:

1. the adding of the handlers in the WaitForPageLoad method is potentially too late. The navigation is initiated before the handlers are added which means that in very rare cases where the browser already has the page it may complete before the handlers are added in which case you will miss the event and sit forever waiting.

   The solution is to add the handlers before the navigation starts and remove them after the navigation completed

   This means the WaitForPageLoad method needs to be split into two methods. One is called before initiating the navigation. It should set the handlers. The second part does the ReadyState monitoring and cleans up when 'Ready'.

2. good programming practices is to add a timeout so that a lost (or crashed, or looping) browser doesn't make your code wait forever for the document completed even

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Sometimes if you use JavaScript the DocumentComplete event don't return the right answer; I use the event ProgressChanged instead:

Private Sub WebBrowser1_ProgressChanged(sender As Object, e As WebBrowserProgressChangedEventArgs) Handles WebBrowser1.ProgressChanged

        Console.WriteLine("Current Progress: " + e.CurrentProgress.ToString)

        If e.CurrentProgress = e.MaximumProgress Then

            ' The maximum progress is reached
            load_started = True

        End If

        ' The page is confirmed downloaded after the progress returns to 0
        If e.CurrentProgress = 0 Then

            If load_started Then

                ' The page is ready to print or download...
                WebBrowser1.Print()
                load_started = False

            End If

        End If

End Sub

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Hold on...

From my experience, you SHOULD make sure that the DocumCompleted belongs to YOUR URL and not to a frame sub-page, script, image, CSS, etc. And that is regardless of the IsBusy or the ReadyState is finished or not, which both are often inaccurate when page is slightly complex.

Well, that is my own personal experience, on a working program of VB.2013 and IE11. Let me also mention that you should take into account also the compatibility mode IE7 which is ON by default at the webBrowser1.

' Page, sub-frame or resource was totally loaded.
Private Sub webBrowser1_DocumentCompleted(sender As Object, _ 
    e As WebBrowserDocumentCompletedEventArgs) _ 
    Handles webBrowser1.DocumentCompleted

    ' Check if finally the full page was loaded (inc. sub-frames, javascripts, etc)
    If e.Url.ToString = webBrowser1.Url.ToString Then
        ' Only now you are sure!
        fullyLoaded = True
    End If

End Sub

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In the load events, use Me.Hide .

In WebBrowser1.DocuementCompleted, use Me.Show

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I struggled with this 'fully loaded' issue for some time but found the following solution worked for me. I'm using IE7, so I'm not sure if this works in other versions, but worth a look.

I split the problem into two parts; first I needed a message from the DocumentComplete event;

Private Sub WebBrowser1_DocumentComplete(ByVal pDisp As Object, URL As Variant)
   fullyLoaded = True
End Sub

Then in the part of code where I need to wait till the web page has fully loaded I call another sub that does this;

Private Sub holdBrowserPage()
     fullyLoaded = False
     Do While fullyLoaded = False
         DoEvents
     Loop 
     fullyLoaded = False
End Sub

In addition, I also needed to do the same thing whilst waiting for javascript code to complete. For instance on one page when you select an item from an html drop down list, it populated the next drop down list, but took a while to reveal itself. In that instance I found calling this;

Private Sub holdBrowser()
Do While WebBrowser1.Busy Or WebBrowser1.ReadyState <> READYSTATE_COMPLETE
   DoEvents
Loop
End Sub

was enough to hold the browser. Not sure if this will help everyone, as a combination of IE7, the website I was loading, and the javascript that the page was running alone might have allowed this solution, but certainly worth a try.

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Another option is to check if it's busy with a timer:

Set the timer as disabled by default. Then whenever navigating, enable it. i.e.:

WebBrowser1.Navigate("https://www.somesite.com")
tmrBusy.Enabled = True

And the timer:

    Private Sub tmrBusy_Tick(sender As Object, e As EventArgs) Handles tmrBusy.Tick

        If WebBrowser1.IsBusy = True Then

            Debug.WriteLine("WB Busy ...")

        Else

            Debug.WriteLine("WB Done.")
            tmrBusy.Enabled = False

        End If

    End Sub

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I made similar function (only that works to me); sorry it is in C# but easy to translate...

private void WaitForPageLoad () {

     while (pageReady == false)
         Application.DoEvents();

     while (webBrowser1.IsBusy || webBrowser1.ReadyState != WebBrowserReadyState.Complete)
         Application.DoEvents();
}