Form.show（）不響應

Question

我正在寫一個小型的postIt程序，它應該使用戶能夠使用數據庫向其他計算機發送小筆記。 我有一個主要的表單，我可以在那裏寫信息並在線查看用戶，一個應該顯示消息的表單以及一個包含用戶和消息表的sql數據庫。

這個想法是，我正在將消息寫入Messagestable，我的程序使用SqlDependency來獲取新消息並將它們顯示在工作表中。到現在爲止還挺好。

問題是，當我添加一個新的消息到我的表SqlDependency觸發一個事件和我的mainForm創建一個新的表後凍結sheet.Show（）被調用後。 mainForm繼續運行，但我的工作表總是不響應。

這裏是我的代碼： DBListener：

Imports System.Data 
    Imports System.Data.Sql 
    Imports System.Data.SqlClient 
    Imports System.Threading 

Public Class DBListener 

    Private changeCount As Integer = 0 

    Private Const tableName As String = "IMSMessages" 
    Private Const statusMessage As String = _ 
     "{0} changes have occurred." 
    Private exitRequested As Boolean = False 
    Private waitInProgress As Boolean = False 
    Private recieverHost As String 
    Private imsMain As IMSMain 

    Public Sub New(main As IMSMain, recieverHost As String) 
     Me.imsMain = main 
     Me.recieverHost = recieverHost 
     initCommand(recieverHost) 
     SqlDependency.Start(connectionString) 
     GetMsg(recieverHost) 
    End Sub 


    Private connectionString As String = "Data Source=NB_RANDY\SQLEXPRESS;Initial Catalog=eurom_test;Integrated Security=SSPI;" 
    Private sqlConn As SqlConnection = New SqlConnection(connectionString) 
    Private commandMesg As SqlCommand = Nothing 
    Private commandUsers As SqlCommand = Nothing 

    Private Sub initCommand(recieverHost As String) 
     commandMesg = New SqlCommand 
     commandMesg.CommandText = "SELECT MessageID,SenderHost,RecieverHost,isRead,isRecieved,Stamp from dbo.IMSMessages " & 
             "WHERE RecieverHost=@RecieverHost" & 
             " AND isRecieved = 0" 
     commandMesg.Parameters.Add("@RecieverHost", SqlDbType.VarChar).Value = recieverHost 
     commandMesg.Connection = sqlConn 

     commandUsers = New SqlCommand 
     commandUsers.CommandText = "Select HostName From dbo.IMSUser" 
    End Sub 




    Private Sub OnChangeMsg(ByVal sender As System.Object, ByVal e As System.Data.SqlClient.SqlNotificationEventArgs) 
     Dim dep As SqlDependency = DirectCast(sender, SqlDependency) 
     RemoveHandler dep.OnChange, AddressOf OnChangeMsg 
     GetMsg(recieverHost) 
    End Sub 
    Private Sub OnChangeUser(ByVal sender As System.Object, ByVal e As System.Data.SqlClient.SqlNotificationEventArgs) 
     Dim dep As SqlDependency = DirectCast(sender, SqlDependency) 
     RemoveHandler dep.OnChange, AddressOf OnChangeUser 
     GetUsers() 
    End Sub 

    Public Sub GetMsg(recieverHost As String) 
     If Not sqlConn.State = ConnectionState.Open Then 
      sqlConn.Open() 

     End If 

     commandMesg.Notification = Nothing 
     Dim dep As SqlDependency = New SqlDependency(commandMesg) 
     AddHandler dep.OnChange, New OnChangeEventHandler(AddressOf OnChangeMsg) 
     Dim table As DataTable = New DataTable 
     Dim adapter As SqlDataAdapter = New SqlDataAdapter(commandMesg) 
     adapter.Fill(table) 
     imsMain.recieveNewMessages(table) 
    End Sub 
    Public Sub GetUsers() 
     If Not sqlConn.State = ConnectionState.Open Then 
      sqlConn.Open() 

     End If 

     commandMesg.Notification = Nothing 
     Dim dep As SqlDependency = New SqlDependency(commandUsers) 
     AddHandler dep.OnChange, New OnChangeEventHandler(AddressOf OnChangeUser) 
     Dim table As DataTable = New DataTable 
     imsMain.updateOnlineUserList() 
    End Sub 


End Class 

IMSMain表格：

Imports System.Data.SqlClient 
    Imports System.Threading 

    Public Class IMSMain 

    Private user As IMSUser 
    Private listener As DBListener 


    Private sqlConn As SqlConnection 

    Public Sub New() 
     InitializeComponent() 
     sqlConn = New SqlConnection("Data Source=NB_RANDY\SQLEXPRESS;Initial Catalog=eurom_test;Integrated Security=SSPI;") 



     Me.user = New IMSUser(My.Computer.Name) 
     user.register() 

     updateOnlineUserList() 
     listener = New DBListener(Me, user.HostName) 

    End Sub 
    Private Sub onSend(sender As Object, e As EventArgs) Handles bt_send.Click 
     Dim command As SqlCommand = New SqlCommand 
     Dim msgText = tb_text.Text 
     Dim reciever As IMSUser = lb_Online.SelectedItem 
     Dim insert_string As String = "Insert INTO dbo.IMSMessages(Text,RecieverHost,SenderHost,isRead,isRecieved,Stamp) Values(@Text,@RecieverHost,@SenderHost,@isRead,@isRecieved,@Stamp)" 
     Dim adapter As SqlDataAdapter = New SqlDataAdapter 
     Dim table As DataTable = New DataTable() 
     Try 

      If Not sqlConn.State = ConnectionState.Open Then 
       sqlConn.Open() 

      End If 
      command.Connection = sqlConn 
      command.CommandText = insert_string 
      adapter.SelectCommand = command 
      adapter.Fill(table) 
      command.CommandText = insert_string 
      command.Parameters.Add("@Text", SqlDbType.VarChar).Value = msgText 
      command.Parameters.Add("@RecieverHost", SqlDbType.NChar).Value = reciever.HostName 
      command.Parameters.Add("@SenderHost", SqlDbType.NChar).Value = user.HostName 
      command.Parameters.Add("@isRecieved", SqlDbType.Bit).Value = 0 
      command.Parameters.Add("@isRead", SqlDbType.Bit).Value = 0 
      command.Parameters.Add("@Stamp", SqlDbType.SmallDateTime).Value = DateTime.Now 
      command.ExecuteNonQuery() 
     Catch ex As Exception 
      Console.WriteLine("onSend: internal database exception" + ex.Message) 
     End Try 
    End Sub 

    Private Sub processMessageId(refMessageID As Integer) 
     Dim command As SqlCommand = New SqlCommand 
     Dim msgID_string As String = "SELECT * from dbo.IMSMessages " & 
             "WHERE MessageID=@MessageID AND isRecieved = 0" & 
             " ORDER BY Stamp" 
     Dim isRecievedUpdate_string As String = "Update dbo.IMSMessages " & 
              "SET isRecieved=1" & 
              " WHERE MessageID=@MessageID" 
     Dim adapter As SqlDataAdapter = New SqlDataAdapter 
     Dim table As DataTable = New DataTable() 
     Try 
      If Not sqlConn.State = ConnectionState.Open Then 
       sqlConn.Open() 

      End If 
      command = New SqlCommand 
      command.CommandText = msgID_string 
      command.Parameters.Add("@MessageID", SqlDbType.Int).Value = refMessageID 
      command.Connection = sqlConn 
      adapter.SelectCommand = command 
      adapter.Fill(table) 
      command = New SqlCommand 
      command.Connection = sqlConn 
      command.CommandText = isRecievedUpdate_string 
      command.Parameters.Add("@MessageID", SqlDbType.Int).Value = refMessageID 
      command.ExecuteNonQuery() 

     Catch ex As Exception 
      Console.WriteLine("processMessageID: internal database exception" + ex.Message) 
     End Try 
     Try 
      Dim row As DataRow = table.Rows(0) 
      Dim senderHost As String = row("SenderHost") 
      Dim sender As IMSUser = New IMSUser(senderHost) 
      Dim currentSheet As IMSSheet 
      Dim stringText As String = row("Text") 
      Dim stamp As Date = row("Stamp") 
      currentSheet = New IMSSheet(sender, stringText, stamp) 
      currentSheet.Show() 
     Catch ex As Exception 
      Console.WriteLine("processMessageID: error while showing sheet") 
     End Try 
    End Sub 

    Public Sub recieveNewMessages(newMessageTable As DataTable) 
     For Each row As DataRow In newMessageTable.Rows 
      Dim id As Integer = row("MessageID") 
      processMessageId(id) 
     Next 
    End Sub 

    Public Sub updateOnlineUserList() 
     lb_Online.Items.Clear() 
     Dim adapter As SqlDataAdapter = New SqlDataAdapter 
     Dim table As DataTable = New DataTable() 
     Dim command As SqlCommand = New SqlCommand 
     Dim onlineUser_string = "Select * FROM dbo.IMSUser" 
     command.CommandText = onlineUser_string 
     Try 
      If Not sqlConn.State = ConnectionState.Open Then 
       sqlConn.Open() 

      End If 
      command.Connection = sqlConn 
      adapter.SelectCommand = command 
      adapter.Fill(table) 
     Catch ex As Exception 
      Console.WriteLine("internal database exception" + ex.Message) 
     End Try 
     For Each row As DataRow In table.Rows 

      Dim tmp As IMSUser = New IMSUser(row("HostName")) 
      If Not user.Equals(tmp) Then 
       lb_Online.Items.Add(tmp) 
      End If 
     Next 
    End Sub 

End Class 

IMSSheet表格：

Public Class IMSSheet 
     Dim IsDraggingForm As Boolean = False 
     Private MousePos As New System.Drawing.Point(0, 0) 

    Public Sub New(session As IMSUser, text As String, stamp As Date) 
     Ini 

tializeComponent() 
      Me.tb_sender.Text = session.HostName 
      addText(text, stamp) 
     End Sub 

     Private Sub addText(msg As String, stamp As DateTime) 
      Dim currentText As String = tb_text.Text 
      currentText = currentText + stamp.ToString + Environment.NewLine + msg + Environment.NewLine 
      tb_text.Text = currentText 
     End Sub 
     Private Sub IMSSheet_MouseDown(ByVal sender As Object, ByVal e As MouseEventArgs) Handles MyBase.MouseDown 
      If e.Button = MouseButtons.Left Then 
       IsDraggingForm = True 
       MousePos = e.Location 
      End If 
     End Sub 

     Private Sub IMSSheet_MouseUp(ByVal sender As Object, ByVal e As MouseEventArgs) Handles MyBase.MouseUp 
      If e.Button = MouseButtons.Left Then IsDraggingForm = False 
     End Sub 

     Private Sub IMSSheet_MouseMove(ByVal sender As Object, ByVal e As MouseEventArgs) Handles MyBase.MouseMove 
      If IsDraggingForm Then 
       Dim temp As Point = New Point(Me.Location + (e.Location - MousePos)) 
       Me.Location = temp 
       temp = Nothing 
      End If 
     End Sub 

     Private Sub onClose(sender As Object, e As EventArgs) Handles bt_Close.Click 
      Me.Close() 
     End Sub 


     Private Sub bt_minimize_Click(sender As Object, e As EventArgs) Handles bt_minimize.Click 
      Me.WindowState = FormWindowState.Minimized 
     End Sub 

     Private Sub bt_Close_MouseHover(sender As Object, e As EventArgs) Handles bt_Close.MouseHover 

     End Sub 

     Private Sub bt_minimize_MouseHover(sender As Object, e As EventArgs) Handles bt_minimize.MouseHover 

     End Sub 
    End Class 

有趣的是，如果我已經有一些新的消息在我運行程序之前在我的Messagestable中，他們將顯示cor rectly。 如果我使用Form.ShowDialog（）顯示工作表，它也可以工作，但它不是我希望它工作的方式。

由於我出於主意，我希望你能幫助我。

Answer 1

您遇到問題，因爲SqlDependency的更改事件發生在與您的UI線程不同的線程上。從SqlDepending documentation：

可在從啓動命令執行 線程不同的線程來生成OnChange事件。

當調用在非UI線程sheet.Show()，Show()會死機因爲沒有消息循環來處理UI事件。在ImsMain上使用Invoke()在您的UI線程上創建並顯示ImsSheet。