Question

我在VB中有一个程序，它在网站中搜索图像如下：

www.website.com/1.jpg | www.website.com/2.jpg | www.website.com/3.jpg

在循环中，程序在浏览器中只打开3.jpg，因为1和2 jpg不会在服务器中退出。该程序已启动并运行，但速度非常慢，一分钟内大约有120次搜索。然而，我的一位同事在Angular中设计了相同的程序，该程序运行速度非常快，一分钟内搜索量大约为500/600。

他告诉我，他所做的是对服务器产生了50次异步调用，然后又产生了50次，然后又50次并继续这样做。从而使他的程序非常快速和准确。

我研究并了解到，在Visual Basic中，我们有异步和等待调用服务器请求，但我无法弄清楚如何。

这是我现有的代码。任何人都可以帮助我。

Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
    Dim MYURL as string
    itemsF = 0

    While Not itemsF = 50000
        MYURL = "www.website.com/" & itemsF & ".jpg"
        CheckPageExists(MYURL)
        itemsF=itemsF+1
    End While
End Sub

Private Function CheckPageExists(ByVal url As String) As Boolean    
    Dim request As Net.HttpWebRequest
    Dim response As Net.HttpWebResponse

    request = Net.WebRequest.Create(url)
    request.Timeout = 5000

    Try
        response = request.GetResponse()
    Catch ex As Exception
        'IMAGE DOES NOT EXITS
        Exit Function
    End Try

    Process.Start(url)
End Function

Answer 1

首先，您必须使CheckPageExists成为Async方法：

Private Async Function CheckPageExists(ByVal url As String) As Task(Of Boolean)
    Dim request As Net.HttpWebRequest = Net.WebRequest.Create(url)
    request.Timeout = 5

    Dim Result As Boolean

    Try
        Using response As HttpWebResponse = Await request.GetResponseAsync.ConfigureAwait(False)
            Using responseReader As New IO.StreamReader(response.GetResponseStream)

                Dim actualResponse As String = Await responseReader.ReadToEndAsync
                Result = True

            End Using
        End Using
    Catch ex As Exception
        'IMAGE DOES NOT EXITS
        Result = False
    End Try

    Console.WriteLine(url)

    ''Process.Start("chrome.exe", url)
    Return Result
End Function

正如您所看到的，我们使用GetResponse而不是GetResponseAsync，而Async本身就是Return。这种方法与你之前做的非常相似，我为了清晰起见，我添加了StreamReader语句，并在Button2_Click添加了Async Function MakeRequests() As Task Dim tasks As List(Of Task(Of Boolean)) = New List(Of Task(Of Boolean)) Dim itemsF As Integer = 5 For i = 1 To itemsF Dim MYURL As String = "http://www.touchegolfschool.com/images/" & i & ".jpg" tasks.Add(CheckPageExists(MYURL)) Next While tasks.Select(Function(x) x.Result).Count < tasks.Count Thread.Sleep(100) End While End Function来阅读您网站的回复。

完成后，您只需更改tasks.Select(Function(x) x.Result).Count < tasks.Count方法即可调用其他方法，其中包含您之前所做的所有操作：

Tasks

主要变化是添加// i tried echoing everything possible but no outcome <?php include("conn.php"); if(isset($_POST['btn_login'])){ $username = $_POST['username']; $password = $_POST['password']; } $sql = "SELECT * FROM users WHERE username='$username' AND password='$password' LIMIT 1"; $result = mysqli_query($conn,$sql); $response = array(); if(mysqli_num_rows($result)>0){ $row = mysqli_fetch_row($result); $username = $row['username']; $password = $row['password']; $code = "login_success"; array_push($response,array("code"=>$code,"username"=>$username,"password"=>$password)); echo json_encode($response); } else{ $code = "login_failed"; $message = "User not found... Please try again"; array_push($response, array("code"=>$code,"message"=>$message)); echo json_encode($response); } mysqli_close($conn); ?> <!DOCTYPE html> <html> <head> <title></title> </head> <body> <form method="post"> <input type="text" name="username"> <input type="text" name="password"> <input type="submit" name="btn_login"> </form> </body> </html>;你之前看到的是一个请求，但由于返回的时间从未返回;告诉主函数等待所有请求都有结果，使应用程序等待足够长的时间来响应。

这里的主要区别在于使用{{1}}。

检查this以获取有关异步编程的官方文档。

我需要在已经运行的程序中使用Async / Await来加快速度

1 个答案: