Question

我正在开发一个小型数据库管理工具。我希望应用程序启动并尝试连接到数据库，但数据库驻留在网络驱动器上，因此可能需要很长时间。在此期间，应用程序挂起。

我使用下面的代码尝试运行代码以连接到不同线程中的数据库，以便应用程序可以加载，并且数据库可以单独连接。

Public Class Incident_Form

    'DELEGATE CLASSES
    Delegate Sub UpdateTable()

    'DELEGATE VARIABLES
    Public UpdateTableVar As UpdateTable

    Private Sub Incident_Form_Load(sender As Object, e As EventArgs) Handles MyBase.Load


        I_List.DataSource = Nothing
        Display_Module.Maximise_Window()

        Splash_Panel.BringToFront()

        System.Windows.Forms.Application.DoEvents()

        UpdateTableVar = New UpdateTable(AddressOf Me.UpdateTableHandler)

        Me.Invoke(Me.UpdateTableVar)


    End Sub



    Public Sub UpdateTableHandler() 'Handles the background work for updating I_LIST
        If (Me.InvokeRequired) Then
            Me.Invoke(UpdateTableVar)
        Else
            Dim myCon = New OleDbConnection(My.Settings.Database_Connection_String)
            myCon.Open()

            Dim ds As DataSet = New DataSet
            Dim adapter As New OleDb.OleDbDataAdapter
            Dim sql As String

            sql = "SELECT [IN_REF], [Incident Name], [Date Created], [Created By] " & _
            "FROM [Master_Record]"

            adapter.SelectCommand = New OleDb.OleDbCommand(sql, myCon)
            adapter.Fill(ds)
            I_List.DataSource = ds.Tables(0)

            I_List.Columns(1).AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill
            I_List.Columns(0).HeaderText = "Reference"

            I_List.Sort(I_List.Columns("Date Created"), System.ComponentModel.ListSortDirection.Descending)

            myCon.Close()
        End If
    End Sub

上述问题是虽然应用程序正确加载并显示表单，但在数据库完成连接之前，用户仍然无法与表单交互。它就像它在另一个线程中运行，但它等待该线程在继续之前完成。

我有什么遗漏或者这不是正确的方法吗？

更新1

感谢您的帮助，我已将代码更新为以下内容并且一切正常：）

Public Class Incident_Form

    Dim ds As DataSet = New DataSet





    Private Sub Incident_Form_Load(sender As Object, e As EventArgs) Handles MyBase.Load


        I_List.DataSource = Nothing
        Display_Module.Maximise_Window()
        Splash_Panel.BringToFront()
        System.Windows.Forms.Application.DoEvents()
        Try
            BackgroundWorker1.RunWorkerAsync()
        Catch ex As Exception
            BackgroundWorker1.WorkerSupportsCancellation = True
            BackgroundWorker1.CancelAsync()
        End Try




    End Sub

    Private Sub BackgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork

        UpdateTableHandler()

    End Sub


    Private Sub BackgroundWorker1_RunWorkerCompleted(ByVal sender As System.Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
        I_List.DataSource = ds.Tables(0)

        I_List.Columns(1).AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill
        I_List.Columns(0).HeaderText = "Reference"

        I_List.Sort(I_List.Columns("Date Created"), System.ComponentModel.ListSortDirection.Descending)
    End Sub


    Public Sub UpdateTableHandler() 'Handles the background work for updating I_LIST

        Dim myCon = New OleDbConnection(My.Settings.Database_Connection_String)
        myCon.Open()


        Dim adapter As New OleDb.OleDbDataAdapter
        Dim sql As String

        sql = "SELECT [IN_REF], [Incident Name], [Date Created], [Created By] " & _
        "FROM [Master_Record]"

        adapter.SelectCommand = New OleDb.OleDbCommand(sql, myCon)
        adapter.Fill(ds)


        myCon.Close()

    End Sub

Answer 1

将DoEvents()来电替换为BackgroundWorker，并将其添加到您的表单中。

Private Sub Incident_Form_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    I_List.DataSource = Nothing
    Display_Module.Maximise_Window()
    Splash_Panel.BringToFront()

    Try
        BackgroundWorker1.RunWorkerAsync()    
    Catch ex As Exception
        BackgroundWorker1p.WorkerSupportsCancellation = True
        BackgroundWorker1.CancelAsync()
    End Try
End Sub

Private Sub BackgroundWorker1_DoWork(sender As Object, e As 
System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork

    UpdateTableHandler()

End Sub

VB.Net在不同的线程上运行任务

1 个答案: