Question

我尝试在名为ProgressBar1的进度条上显示百分比进度，现在创建了一个名为BackGrounWorker的{{1}}并且我有以下代码：

BkW1

现在我的Private Sub Form1_Load(sender as Object, e As EventArgs) Handles MyBase.Load BKW1.RunWorkerAsync() End Sub Private Sub BKW1_DoWork(sender As Object, e As DoWorkEventArgs) Handles BKW1.DoWork ExternalClass.MyFunction() 'This function is located in another class End Sub Private Sub BKW1_ProgressChanged(sender As Object, e As ProgressChangedEventArgs) Handles BKW1.ProgressChanged Invoke(Sub() ProgressBar1.Value = e.ProgressPercentage End Sub) End Sub会遍历ExternalClass.MyFunction()上可用的所有记录。为什么BackGroundWorker不会在ProgressBar1上显示百分比？我应该在我的外部函数中插入一些引用？

Answer 1

您必须指定BackgroundWorker实际显示进度（因此在Form_Load中）：

BKW1.WorkerReportsProgress= True

然后你必须实际告诉它报告DoWork方法的进度（这会触发ProgressChanged事件）：

BKW1.ReportProgress(x)

因此，您可能需要ExternalClass提出ProgressChanged事件并在此处调用此行。这是一个简化的例子：

Public Class ExternalClass
    Public Event ProgressChanged(percentage As Integer)

    Public Function MyFunction() As Boolean
        For i As Integer = 0 To 100
            'do something
            'report the progress
            RaiseEvent ProgressChanged(i)
        Next
        Return True
    End Function
End Class

Private Sub BackgroundWorker1_DoWork(sender As Object, e As DoWorkEventArgs) Handles BackgroundWorker1.DoWork
    Dim MyExternalClass As New ExternalClass
    AddHandler MyExternalClass.ProgressChanged, Sub(x) ExternalClass_ProgressChanged(x)
    MyExternalClass.MyFunction
End Sub

Private Sub ExternalClass_ProgressChanged(percentage As Integer)
    BackgroundWorker1.ReportProgress(percentage)
End Sub

Private Sub BackgroundWorker1_ProgressChanged(sender As Object, e As ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged
    ProgressBar1.value = e.ProgressPercentage
End Sub

请注意，您实际上不需要调用BKW1_ProgressChanged事件中的方法，因为它在UI线程上运行。这就是BackgroundWorker更方便使用的原因。

Answer 2

您是否尝试在每个循环中在Sub BKW1_DoWork中引发事件ReportProgress（）？否则，将不会触发事件ProgressChanged。

这里有一些有趣的代码可以帮助您：http://www.vb-helper.com/howto_net_use_backgroundworker.html

BackgroundWorker控件不显示百分比进度

2 个答案: