WebBrowser，处理pdf加载完成

Question

我想知道是否有人知道让 .pdf 文件在加载时触发就绪状态的简单方法。我正在构建一个程序来打开 url 并截取屏幕截图，然后将它们放入 excel 中。

网络浏览器将正确加载 html 文档，但在加载 .pdf 文件时卡在 While Not pageready 中。浏览器控件正确呈现.pdf。

Private Sub btngo_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btngo.Click
    Dim file As String
    Dim Obj As New Object
    Dim result As String
    Dim sheet As String = "sheet1"
    Dim xlApp As New Excel.Application

    If lblpath.Text <> "" Then
        file = lblpath.Text
        Dim xlWorkBook = xlApp.Workbooks.Open(file)
        Dim xlWorkSheet = xlWorkBook.Worksheets(sheet)
        Dim range = xlWorkSheet.UsedRange

        ProgressBar1.Value = 0

        For rCnt = 4 To range.Rows.Count
            'url cell
            Obj = CType(range.Cells(rCnt, 2), Excel.Range)
            ' Obj.value now contains the value in the cell.. 
            Try
                ' Creates an HttpWebRequest with the specified URL. 
                Dim myHttpWebRequest As HttpWebRequest = CType(WebRequest.Create(Obj.value), HttpWebRequest)
                ' Sends the request and waits for a response. 
                Dim myHttpWebResponse As HttpWebResponse = CType(myHttpWebRequest.GetResponse(), HttpWebResponse)
                If myHttpWebResponse.StatusCode = HttpStatusCode.OK Then
                    result = myHttpWebResponse.StatusCode
                    WebBrowser1.ScrollBarsEnabled = False
                    WebBrowser1.Navigate(myHttpWebRequest.RequestUri)

                    WaitForPageLoad()

                    CaptureWebBrowser(WebBrowser1)
                End If
                ' Release the resources of the response.
                myHttpWebResponse.Close()

            Catch ex As WebException
                result = (ex.Message)
            Catch ex As Exception
                result = (ex.Message)
            End Try


            RichTextBox1.AppendText(result & "    " & Obj.value & vbNewLine)

            If radpre.Checked = True Then
                range.Cells(rCnt, 3).value = result
            ElseIf radcob.Checked = True Then
                range.Cells(rCnt, 4).value = result
            ElseIf radpost.Checked = True Then
                range.Cells(rCnt, 5).value = result

            End If


            ProgressBar1.Value = rCnt / range.Rows.Count * 100
        Next

        With xlApp
            .DisplayAlerts = False
            xlWorkBook.SaveAs(lblpath.Text.ToString)
            .DisplayAlerts = True
        End With

        xlWorkBook.Close()
        xlApp.Quit()

        'reclaim memory
        Marshal.ReleaseComObject(xlApp)
        xlApp = Nothing
    End If
End Sub

Private Function CaptureWebBrowser(ByVal wb As WebBrowser) As Image
    Try
        Dim hBitmap As Bitmap = New Bitmap(wb.Width, wb.Height)
        wb.DrawToBitmap(hBitmap, wb.Bounds)
        Dim img As Image = hBitmap
        Return img
    Catch ex As Exception
        MessageBox.Show(ex.Message)
    End Try
    Return Nothing
End Function


Private Sub WaitForPageLoad()
    AddHandler WebBrowser1.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 WebBrowser1.ReadyState = WebBrowserReadyState.Complete Then
        pageready = True
        RemoveHandler WebBrowser1.DocumentCompleted, New WebBrowserDocumentCompletedEventHandler(AddressOf PageWaiter)
    End If
End Sub

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更新到已解决

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我对反馈感到非常满意。我真的很喜欢Noseratio 提供的答案。我不知道使用代码模式不是最佳实践。打开 .pdf 或任何其他非基于 Web 的文档时，readyState 将永远不会更改为 0。看到这个程序对我来说只是一种不工作的方式，我很满意只捕获.html 和.htm。

我的要求是

1. 打开excel文档
2. 解析位于 excel 文档中的链接
3. 确定响应代码
4. 将响应代码和屏幕截图写入 excel

程序解析和检索反馈的速度远快于我手动完成的速度。 .html 和 .htm 的屏幕截图为非技术人员提供了成功从生产环境迁移到 COB 并返回生产环境的 excel 文件证明。

Noseratio 所述的代码没有遵循最佳实践，也不是高质量的。这是一个快速而肮脏的实现。

Option Infer On
Imports Microsoft.Office.Interop
Imports System.Net
Imports System.Runtime.InteropServices

Public Class Form1


Public Property pageready As Boolean

Private Sub OpenToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OpenToolStripMenuItem.Click
    OpenFileDialog1.ShowDialog()
End Sub

Private Sub OpenFileDialog1_FileOk(ByVal sender As System.Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles OpenFileDialog1.FileOk
    lblpath.Text = OpenFileDialog1.FileName.ToString
End Sub

Private Sub btngo_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btngo.Click
    Dim file As String
    Dim Obj As New Object
    Dim result As String
    Dim sheet As String = "sheet1"
    Dim xlApp As New Excel.Application
    Dim img As Bitmap
    Dim path As String = "C:\Documents and Settings\user\My Documents\Visual Studio 2010\Projects\COB-HTML-Tool\COB-HTML-Tool\bin\Debug\tmp.bmp"
    If lblpath.Text <> "" Then
        file = lblpath.Text
        Dim xlWorkBook = xlApp.Workbooks.Open(file)
        Dim xlWorkSheet = xlWorkBook.Worksheets(sheet)
        Dim range = xlWorkSheet.UsedRange

        ProgressBar1.Value = 0

        For rCnt = 4 To range.Rows.Count
            'url cell
            Obj = CType(range.Cells(rCnt, 2), Excel.Range)
            ' Obj.value now contains the value in the cell.. 
            Try
                ' Creates an HttpWebRequest with the specified URL. 
                Dim myHttpWebRequest As HttpWebRequest = CType(WebRequest.Create(Obj.value), HttpWebRequest)
                ' Sends the request and waits for a response. 
                Dim myHttpWebResponse As HttpWebResponse = CType(myHttpWebRequest.GetResponse(), HttpWebResponse)
                If myHttpWebResponse.StatusCode = HttpStatusCode.OK Then
                    result = myHttpWebResponse.StatusCode


                    Dim len As Integer = myHttpWebRequest.RequestUri.ToString.Length - 4
                    If myHttpWebRequest.RequestUri.ToString.Substring(len) = ".htm" Or
                        myHttpWebRequest.RequestUri.ToString.Substring(len - 1) = ".html" Or
                        myHttpWebRequest.RequestUri.ToString.Substring(len) = ".asp" Then
                        WebBrowser1.Navigate(myHttpWebRequest.RequestUri)
                        WaitForPageLoad()

                        img = CaptureWebBrowser(WebBrowser1)
                        img.Save(path)
                    End If

                End If
    ' Release the resources of the response.
    myHttpWebResponse.Close()

            Catch ex As WebException
        result = (ex.Message)
    Catch ex As Exception
        result = (ex.Message)
    End Try


            RichTextBox1.AppendText(result & "    " & Obj.value & vbNewLine)

            If radpre.Checked = True Then
                range.Cells(rCnt, 3).value = result

                If img Is Nothing Then
                Else
                    If Dir(path) <> "" Then
                        range.Cells(rCnt, 4).Select()
                        Dim opicture As Object
                        opicture = xlApp.ActiveSheet.Pictures.Insert(path)
                        opicture.ShapeRange.LockAspectRatio = True
                        opicture.ShapeRange.width = 170
                        opicture.ShapeRange.height = 170
                        My.Computer.FileSystem.DeleteFile(path)

                    End If
                End If
            ElseIf radcob.Checked = True Then
                range.Cells(rCnt, 5).value = result
                If img Is Nothing Then
                Else
                    If Dir(path) <> "" Then
                        range.Cells(rCnt, 6).Select()
                        Dim opicture As Object
                        opicture = xlApp.ActiveSheet.Pictures.Insert(path)
                        opicture.ShapeRange.LockAspectRatio = True
                        opicture.ShapeRange.width = 170
                        opicture.ShapeRange.height = 170
                        My.Computer.FileSystem.DeleteFile(path)
                    End If
                End If
            ElseIf radpost.Checked = True Then
                range.Cells(rCnt, 7).value = result
                If img Is Nothing Then
                Else
                    If Dir(path) <> "" Then
                        range.Cells(rCnt, 8).Select()
                        Dim opicture As Object
                        opicture = xlApp.ActiveSheet.Pictures.Insert(path)
                        opicture.ShapeRange.LockAspectRatio = True
                        opicture.ShapeRange.width = 170
                        opicture.ShapeRange.height = 170
                        My.Computer.FileSystem.DeleteFile(path)
                    End If
                End If
            End If


            ProgressBar1.Value = rCnt / range.Rows.Count * 100
        Next

        With xlApp
            .DisplayAlerts = False
            xlWorkBook.SaveAs(lblpath.Text.ToString)
            .DisplayAlerts = True
        End With

        xlWorkBook.Close()
        xlApp.Quit()

        'reclaim memory
        Marshal.ReleaseComObject(xlApp)
        xlApp = Nothing
    End If
End Sub
Private Function CaptureWebBrowser(ByVal wb As WebBrowser) As Image

    Try
        wb.ScrollBarsEnabled = False
        Dim hBitmap As Bitmap = New Bitmap(wb.Width, wb.Height)
        wb.DrawToBitmap(hBitmap, wb.Bounds)
        Dim img As Image = hBitmap
        Return img
    Catch ex As Exception
        MessageBox.Show(ex.Message)
    End Try
    Return Nothing
End Function


Private Sub WaitForPageLoad()
    AddHandler WebBrowser1.DocumentCompleted, New WebBrowserDocumentCompletedEventHandler(AddressOf PageWaiter)
    While Not pageready
        Application.DoEvents()
        System.Threading.Thread.Sleep(200)
    End While
    pageready = False
End Sub

Private Sub PageWaiter(ByVal sender As Object, ByVal e As WebBrowserDocumentCompletedEventArgs)
    If WebBrowser1.ReadyState = WebBrowserReadyState.Complete Then
        pageready = True
        RemoveHandler WebBrowser1.DocumentCompleted, New WebBrowserDocumentCompletedEventHandler(AddressOf PageWaiter)
    End If
End Sub


End Class

Answer 1

很遗憾，您将无法使用webBrowser.DrawToBitmap 获取 PDF 视图的快照。在撰写本文时，Adobe Acrobat Reader ActiveX 控件不支持在自定义设备上下文上呈现，因此此方法不起作用，以及发送WM_PRINT 或调用IViewObject::Draw ，或者直接在通过 WebBrowser 上的 Reader ActiveX 对象上（我试过了，I'm not alone）。正确的解决方案是使用第 3 方 PDF 渲染组件。

附带说明，您应该避免使用这样的代码模式：

While Not pageready
    Application.DoEvents()
End While

这是一个busy waiting 紧密循环，徒劳地消耗 CPU 周期。至少，在循环中添加一些Thread.Sleep(200)，但总体而言，您也应该避免使用using Application.DoEvents。