Question

我的问题是vb.net中的后台工作者不允许执行一行代码这是代码：

  Private _worker As BackgroundWorker

Public Sub startload(ByVal e As System.EventArgs)
    _worker = New BackgroundWorker()
    AddHandler _worker.DoWork, AddressOf WorkerDoWork
    AddHandler _worker.RunWorkerCompleted, AddressOf WorkerCompleted

    _worker.RunWorkerAsync()
End Sub

Public Sub WorkerDoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs)
    objRpt = New CRBooks
    con.ConnectionString = ConnStr.Connstring
    Dim query As String = CreateSelectQueryAndParameters()
    'if there is no item select, then exit from the method.
    If Not query.Contains("Column") Then
        MessageBox.Show("No selection to display!")
        Return
    End If
    Try
        Dim adapter As MySqlDataAdapter = New MySqlDataAdapter(query, con)
        Dim Ds As Books = New Books
        adapter.Fill(Ds, "Books")
        objRpt.SetDataSource(Ds)
        MsgBox(Ds.Tables(0).Rows(0).Item(0))
        frmReports.CrystalReportViewer1.ReportSource = objRpt
    Catch oleEx As MySqlException
        MessageBox.Show(oleEx.Message)
    Catch Ex As Exception
        MessageBox.Show(Ex.Message)
    End Try
End Sub


Private Sub WorkerCompleted(ByVal sender As Object, ByVal e As RunWorkerCompletedEventArgs)
    Me.Close()
End Sub

frmReports.CrystalReportViewer1.ReportSource = objRpt这一行并没有执行但是当我试图断点时，编译器会运行该行，但不会执行。

Answer 1

不幸的是，您已为水晶报表查看器指定了报表源，但要查看该报表查看器，您应该调用包含报表查看器的相应表单的show方法来查看该报表。

使用此代码。

Public Sub WorkerDoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs)
    objRpt = New CRBooks
    con.ConnectionString = ConnStr.Connstring
    Dim query As String = CreateSelectQueryAndParameters()
    'if there is no item select, then exit from the method.
    If Not query.Contains("Column") Then
        MessageBox.Show("No selection to display!")
        Return
    End If
    Try
        Dim adapter As MySqlDataAdapter = New MySqlDataAdapter(query, con)
        Dim Ds As Books = New Books
        adapter.Fill(Ds, "Books")
        objRpt.SetDataSource(Ds)
        MsgBox(Ds.Tables(0).Rows(0).Item(0))
        frmReports.CrystalReportViewer1.ReportSource = objRpt
        frmReports.CrystalReportViewer1.Refreshreport()
        frmReports.show()
    Catch oleEx As MySqlException
        MessageBox.Show(oleEx.Message)
    Catch Ex As Exception
        MessageBox.Show(Ex.Message)
    End Try
End Sub

此处frmReports.show显示包含报告查看器的表单。

VB.NET后台工作程序不执行水晶报表查看器报表源

1 个答案: