Question

我已经编写了以下代码，以完成在机器上导出打印机详细信息的任务。下面的代码可以正常工作。

通常，生成打印机详细信息文件需要花费几秒钟或更长时间，因此，我想在标签或文本框中显示此过程的状态（例如“正在生成文件。请稍候...”， “文件已生成。”等）

我无法使用以下代码在标签上获得正确的状态。它直接显示“文件已生成”状态。但是，如果将消息框放在while循环之前和之后，则可以正常工作。

任何帮助都非常有帮助。谢谢。

Label1.Text = "Status: File is being generated. Please wait.."

Dim pPrintBrm As New ProcessStartInfo
pPrintBrm.FileName = "C:\Windows\System32\spool\tools\PrintBrm.exe"
pPrintBrm.Arguments = " " & "-B" & " " & "-F" & " " & 
My.Computer.FileSystem.CurrentDirectory & "\Extracted\Printer.PrinterExport"
pPrintBrm.WindowStyle = ProcessWindowStyle.Hidden
Process.Start(pPrintBrm)

Dim exists As Boolean = File.Exists(My.Computer.FileSystem.CurrentDirectory & "\Extracted\Printer.PrinterExport")

MessageBox.Show("before while " & exists)

While (exists = "False")

exists = File.Exists(My.Computer.FileSystem.CurrentDirectory & "\Extracted\Printer.PrinterExport")

End While

MessageBox.Show("after while " & exists)

If File.Exists(My.Computer.FileSystem.CurrentDirectory & "\Extracted\Printer.PrinterExport") Then

Label1.Text = "Status: File is generated"
Else
Label1.Text = "Status: Failed"
End If

Answer 1

使用BackgroundWorker组件，然后在Background Worker的DoWork事件中执行此代码，并通过BackgroundWorker.ReportProgress（）在标签上显示所有更新状态

Answer 2

您可以使用Async/Await使应用程序在循环中保持响应状态：

Private Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Label1.Text = "Status: File is being generated. Please wait.."

    Dim pPrintBrm As New ProcessStartInfo
    pPrintBrm.FileName = "C:\Windows\System32\spool\tools\PrintBrm.exe"
    pPrintBrm.Arguments = " " & "-B" & " " & "-F" & " " &
    My.Computer.FileSystem.CurrentDirectory & "\Extracted\Printer.PrinterExport"
    pPrintBrm.WindowStyle = ProcessWindowStyle.Hidden
    Process.Start(pPrintBrm)

    Dim exists As Boolean
    Do
        Await Task.Delay(250) ' <-- code pauses here, but the UI is still responsive and updates
        exists = File.Exists(My.Computer.FileSystem.CurrentDirectory & "\Extracted\Printer.PrinterExport")
    Loop While (Not exists)

    If exists Then
        Label1.Text = "Status: File is generated"
    Else
        Label1.Text = "Status: Failed" ' <-- how can you ever get here with the above loop?!
    End If
End Sub

请注意，子声明已标记为“异步”。

无法在VB.Net中显示进程的当前状态

2 个答案: