VB.net使用CefSharp笔记
作者:admin 日期:2023-01-13
获取js执行返回值
Imports CefSharp.WinForms
Public Class Form1
'定义cef浏览器控件的全局变量,方便后面调用,注意WithEvents
Private WithEvents browser As ChromiumWebBrowser
Public Sub New()
' 此调用是设计器所必需的。
InitializeComponent()
' 设置cef控件菜单语言为中文
Dim settings As New CefSettings() With {
.Locale = "zh-CN"
}
CefSharp.Cef.Initialize(settings)
'初始化cef浏览器控件样式和默认打开的地址，并将其加入到Panel控件中
browser = New ChromiumWebBrowser("about:blank") With {
.Dock = DockStyle.Fill
}
Panel2.Controls.Add(browser)
'手动跳转新的地址
browser.Load("http://mail.qq.com")
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
'从textbox中获取内容当做url扔给cef访问
Dim url = TextBox1.Text
browser.Load(url)
End Sub
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
'调用cef执行js代码并返回结果，这里使用js原生函数querySelector通过css选择器获取dom的值
Dim js As String = "document.querySelector('.login_pictures_txt').innerText"
Dim html_task As Task(Of JavascriptResponse) = browser.EvaluateScriptAsync(js, timeout:=Nothing)
'阻塞等待task任务结束
html_task.Wait()
RichTextBox1.Text = html_task.Result.Result
End Sub
End Class
获取异步加载页面的HTML代码
比较简单粗暴有效的方法:使用Timer循环在页面中执行js通过css选择器去找加载完成后才会出现的dom元素个数,大于0则可认定为页面加载完成了.
Imports CefSharp
Imports CefSharp.WinForms
Public Class SingleBrowser
Private browser As ChromiumWebBrowser
Private WithEvents get_html_tm As New Timer() With {.Interval = 200} '获取页面HTML的计时器
Public Sub New()
' 此调用是设计器所必需的。
InitializeComponent()
' 在 InitializeComponent() 调用之后添加任何初始化。
Dim settings As New CefSettings With {
.Locale = "zh-CN",
.CachePath = Application.StartupPath & "\Cache"
}
CefSharp.Cef.Initialize(settings)
browser = New ChromiumWebBrowser("about:blank") With {
.Dock = DockStyle.Fill
}
Panel2.Controls.Add(browser)
End Sub
Private Sub startBtn_Click(sender As Object, e As EventArgs) Handles startBtn.Click
'处理URL路由
Dim url As String = url_textbox.Text
'加载文本框中的地址,比如淘宝的搜索结果页面
browser.Load(url)
'开始计时器工作
get_html_tm.Start()
End Sub
''' <summary>
''' 判断淘宝搜索结果页面是否加载完毕
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
Private Async Sub get_html_tick(sender As Object, e As EventArgs) Handles get_html_tm.Tick
Dim js As String = "document.querySelectorAll('.pic-link').length"
Dim result As Integer = doJs(js)
If result > 0 Then
get_html_tm.Stop()
'加载完毕,开始获取HTML内容
Dim html As String = Await browser.GetSourceAsync()
Console.WriteLine("----加载HTML成功")
Console.Write(html)
End If
End Sub
''' <summary>
''' 在浏览器中执行js
''' </summary>
''' <param name="js"></param>
''' <returns>返回js执行结果,object对象或者nothing</returns>
Private Function doJs(ByVal js As String)
If Not browser.IsLoading Then
Dim js_task As Task(Of JavascriptResponse) = browser.EvaluateScriptAsync(js)
js_task.Wait()
Return js_task.Result.Result
Else
Return Nothing
End If
End Function
End Class
使用AngleSharp解析HTML
Public Class SingleBrowser
Private parser As New AngleSharp.Parser.Html.HtmlParser() 'HTML解析器
Private Sub dealHtml(Byval html as String)
'解析HTML为AngleSharp的IHtmlDocument对象
Dim doc = parser.Parse(html)
'通过css选择器筛选出符合条件的dom元素集合
Dim link_list = doc.QuerySelectorAll(".pic-link")
'遍历dom集合进行处理
For Each link In link_list
'获取dom的文本内容
Console.WriteLine(link.TextContent())
'获取dom的属性href
Console.WriteLine(link.GetAttribute("href"))
Next
End Sub
使用offscreen在后台隐式获取指定页面的HTML
注意：需要另外从NuGet上安装CefSharp.Offscreen的包包
Imports CefSharp
Imports CefSharp.OffScreen
Public Class offscreen
Private browser As ChromiumWebBrowser
Public Sub New()
' 此调用是设计器所必需的。
InitializeComponent()
' 允许多线程间修改主UI线程的控件内容
CheckForIllegalCrossThreadCalls = False
Dim settings As New CefSettings() With {
.Locale = "zh-CN"
}
CefSharp.Cef.Initialize(settings)
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Try
browser = New ChromiumWebBrowser("mail.qq.com")
AddHandler browser.LoadingStateChanged, AddressOf doneLoad
Catch ex As Exception
TextBox1.Text = ex.Message
End Try
End Sub
''' <summary>
''' 处理browser对象加载状态发生改变时的事件
''' 注意括号中的参数必须与browser.LoadingStateChanged签名一致
''' 所谓签名一致，就是括号里面参数的数量、类型一致（不知道这样理解对不对） '''
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
Private Async Sub doneLoad(ByVal sender As Object, ByVal e As LoadingStateChangedEventArgs)
'如果browser不是处于loading状态
If Not e.IsLoading Then
'移除绑定的当前事件(即当前事件只触发一次)
RemoveHandler browser.LoadingStateChanged, AddressOf doneLoad
'手动设置的等待1秒,让browser渲染完毕
Threading.Thread.Sleep(1000)
'阻塞等待(异步)获取browser中的源代码
Dim html As String = Await browser.GetSourceAsync()
TextBox1.Text = html
End If
End Sub
End Class
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