Question

实现异步下载

我已将事件处理程序定义如下：

 Private Sub DownloadCompleted(sender As Object, e As DownloadDataCompletedEventArgs)
        Dim bytes() As Byte = e.Result
        'do somthing with result
    End Sub

但是我需要将下载的结果与我创建URI的值一起传递给此事件处理程序一个附加参数。例如：

Dim pictureURI = "http://images.server.sample.com/" + myUniqueUserIdentifier

我需要在myUniqueUserIdentifier sub。

中回调DownloadCompleted

我正在使用以下代码注册我的事件处理程序：

AddHandler webClient.DownloadDataCompleted, AddressOf DownloadCompleted

我只有一个猜测，扩展WebClient对象并覆盖DownloadDataCompleted对象。但是在我要执行此操作之前，我想检查是否有更简单的解决方案？

谢谢。

Answer 1

您可以使用带有其他对象的the Eclipse documentation for Services重载，然后通过WebClient.DownloadDataAsync属性再次接收它。

以下是一个例子：

Sub Main
    Dim url = "http://google.com"
    Dim client = new WebClient()
    AddHandler client.DownloadDataCompleted, AddressOf DownloadDataCompleted
    client.DownloadDataAsync(new Uri(url), url) ' <- pass url as additional information...'
End Sub

Sub DownloadDataCompleted(sender as object, e as DownloadDataCompletedEventArgs)
    Dim raw as byte() = e.Result
    ' ... and recieve it in the event handler via the UserState property'
    Console.WriteLine(raw.Length & " bytes received from " & e.UserState.ToString())
End Sub

Answer 2

您可以使用函数来传递参数而不是AddressOf

AddHandler webClient.DownloadDataCompleted, Function(sender, e) DownloadCompleted(param)

使用DownloadDataCompleted方法

2 个答案: