通过 WebBrowser 下载鼠标指针下的图像

此代码允许使用标准的 WebBrowser 控件导航到 Google 图片搜索页面，并通过鼠标右键单击来选择/下载图片.

This code allow to use a standard WebBrowser control to navigate to the Google Image search page and select/download an Image with a right-click of the Mouse.

要对其进行测试，请将 WebBrowser Control 和 FlowLayoutPanel 放在 Form 上，然后导航到 Google Image 搜索页面.

To test it, drop a WebBrowser Control and a FlowLayoutPanel on a Form and navigate to a Google Image search page.

注意事项:

• WebBrowser.DocumentCompleted:每次完成主 HtmlDocument 页面中的一个子文档时，都会引发此事件.因此，它可以多次提升.我们需要检查WebBrowser.ReadyState = WebBrowserReadyState.Complete.
  请阅读有关此内容的说明:如何在 Frames/IFrames 中获取 HtmlElement 值?
• Google 搜索页面中的图像可以通过两种不同的方式插入到文档中:使用 Base64Encoded 字符串 和使用经典的 src=[URI] 格式.我们需要准备好两者兼得.
• 鼠标点击位置可以以绝对坐标或相对坐标表示，由 e.ClientMousePosition 或 e.OffsetMousePosition.
  在此处阅读有关此功能的说明:在 WebBrowser 文档中获取鼠标单击坐标
• WebBrowser 仿真模式可能很重要.我们应该使用当前机器中可用的最新兼容模式.
  阅读此答案并应用所需的修改以提供最新的 Internet Explorer 模式:如何让 WebBrowser 控件显示现代内容?.

• WebBrowser.DocumentCompleted: This event is raised each time one of the Sub-Documents inside a main HtmlDocument page is completed. Thus, it can be raised multiple times. We need to check whether the WebBrowser.ReadyState = WebBrowserReadyState.Complete.
  Read these note about this: How to get an HtmlElement value inside Frames/IFrames?
• The images in the Google search page can be inserted in the Document in 2 different manners: both using a Base64Encoded string and using the classic src=[URI] format. We need to be ready to get both.
• The mouse click position can be espressed in either absolute or relative coordinates, referenced by the e.ClientMousePosition or e.OffsetMousePosition.
  Read the notes about this feature here: Getting mouse click coordinates in a WebBrowser Document
• The WebBrowser emulation mode can be important. We should use the most recent compatible mode available in the current machine.
  Read this answer and apply the modifications needed to have the most recent Internet Explorer mode available: How can I get the WebBrowser control to show modern contents?.

请注意，事件处理程序在当前文档完成时连接，并在浏览器导航到另一个页面时删除.这可以防止对 DocumentCompleted 事件的意外调用.

Note that an event handler is wired up when the current Document is completed and is removed when the Browser navigates to another page. This prevents undesired calls to the DocumentCompleted event.

当前文档完成后，在图像上单击鼠标右键，会创建一个新的 PictureBox 控件，该控件将添加到 FlowLayouPanel 以进行演示.

When the current Document is complete, clicking with the right button of the Mouse on an Image, creates a new PictureBox control that is added to a FlowLayouPanel for presentation.

鼠标点击处理程序中的代码(Protected Sub OnHtmlDocumentClick())检测当前图像是否为Base64Encoded 字符串或外部源 URI.
在第一种情况下，它调用 Convert.FromBase64String要将字符串转换为 Byte 数组，在第二种情况下，它使用 WebClient 类将图像下载为 Byte 数组.

The code in the Mouse click handler (Protected Sub OnHtmlDocumentClick()) detects whether the current image is a Base64Encoded string or an external source URI.
In the first case, it calls Convert.FromBase64String to convert the string into a Byte array, in the second case, it uses a WebClient class to download the Image as a Byte array.

在这两种情况下，然后将数组传递给另一个方法(Private Function GetBitmapFromByteArray())，该方法使用 Image.FromStream() 和一个用 Byte 数组初始化的 MemoryStream.

In both cases, the array is then passed to another method (Private Function GetBitmapFromByteArray()) that returns an Image from the array, using Image.FromStream() and a MemoryStream initialized with the Byte array.

此处的代码不执行空检查和类似的防故障测试.应该的，这取决于你.

The code here is not performing null checks and similar fail-proof tests. It ought to, that's up to you.

Public Class frmBrowser
    Private WebBrowserDocumentEventSet As Boolean = False
    Private base64Pattern As String = "base64,"

    Private Sub frmBrowser_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        WebBrowser1.ScriptErrorsSuppressed = True
        WebBrowser1.IsWebBrowserContextMenuEnabled = False
    End Sub

    Private Sub WebBrowser1_DocumentCompleted(sender As Object, e As WebBrowserDocumentCompletedEventArgs) Handles WebBrowser1.DocumentCompleted
        If WebBrowser1.ReadyState = WebBrowserReadyState.Complete AndAlso WebBrowserDocumentEventSet = False Then
            WebBrowserDocumentEventSet = True
            AddHandler WebBrowser1.Document.MouseDown, AddressOf OnHtmlDocumentClick
        End If
    End Sub

    Protected Sub OnHtmlDocumentClick(sender As Object, e As HtmlElementEventArgs)
        Dim currentImage As Image = Nothing

        If Not (e.MouseButtonsPressed = MouseButtons.Right) Then Return
        Dim source As String = WebBrowser1.Document.GetElementFromPoint(e.ClientMousePosition).GetAttribute("src")

        If source.Contains(base64Pattern) Then
            Dim base64 As String = source.Substring(source.IndexOf(base64Pattern) + base64Pattern.Length)
            currentImage = GetBitmapFromByteArray(Convert.FromBase64String(base64))
        Else
            Using wc As WebClient = New WebClient()
                currentImage = GetBitmapFromByteArray(wc.DownloadData(source))
            End Using
        End If

        Dim p As PictureBox = New PictureBox() With {
            .Image = currentImage,
            .Height = Math.Min(FlowLayoutPanel1.ClientRectangle.Height, FlowLayoutPanel1.ClientRectangle.Width)
            .Width = .Height,
            .SizeMode = PictureBoxSizeMode.Zoom
        }
        FlowLayoutPanel1.Controls.Add(p)
    End Sub

    Private Sub WebBrowser1_Navigating(sender As Object, e As WebBrowserNavigatingEventArgs) Handles WebBrowser1.Navigating
        If WebBrowser1.Document IsNot Nothing Then
            RemoveHandler WebBrowser1.Document.MouseDown, AddressOf OnHtmlDocumentClick
            WebBrowserDocumentEventSet = False
        End If
    End Sub

    Private Function GetBitmapFromByteArray(imageBytes As Byte()) As Image
        Using ms As MemoryStream = New MemoryStream(imageBytes)
            Return DirectCast(Image.FromStream(ms).Clone(), Image)
        End Using
    End Function
End Class