跨线程操作无效：控制“comboBoxLocation”从比它是在

Question

创建我新的线程和我收到此错误

跨线程操作无效的线程以外的线程访问：控制'comboBoxLocation'从其创建线程以外的线程访问 。

我不知道我是否正确创建这个线程，但每次它给我的错误。有谁知道如何解决这个问题。我已经尝试过了：

this.Invoke(new MethodInvoker(delegate() 
{ 
    da.SelectCommand.Parameters.AddWithValue("@QueueID", comboBoxLocation.SelectedValue.ToString()); 
})); 

而且我仍然遇到那个错误。

string branch; 
SpeechSynthesizer reader = new SpeechSynthesizer(); 
Thread t; 
bool flag; 

//SqlDataReader dr2; 
public Main() 
{ 
    InitializeComponent(); 
} 

private void btnStart_Click(object sender, EventArgs e) 
{ 
    lblStatus.Text = "Started!"; 
    btnStop.Enabled = true; 
    btnStart.Enabled = false; 
    t = new Thread(Begin); //calls Begin method 
    t.Name = "Queue"; //thread name 
    t.Start(); //Starts thread 
    flag = false; 
    branch = comboBoxLocation.SelectedValue.ToString(); 
} 

private void btnStop_Click(object sender, EventArgs e) 
{ 
    lblStatus.Text = "Voice Application Termintated!"; 
    btnStart.Enabled = true; 
    btnStop.Enabled = false; 
    t.Abort(); //Kills Thread 
    flag = true; 
}  

//Began method 
public void Begin() 
{ 
    double announce; 
    double announceID; 

    string Stringannounce; 
    string ticketNum, station, id, displaynum; 
    string speak; 

    try 
    { 
     using (SqlConnection connStr = new SqlConnection(ConfigurationManager.ConnectionStrings["AnnounceConnString"].ConnectionString)) 
     { 
      while (true) 
      { 
       //Selects Last record written to tblAnnounce 
       SqlCommand sqlcommandStart = new SqlCommand("SELECT id, AnnounceID, AddDate FROM tblAnnounce ORDER by AddDate ASC", connStr); 
       connStr.Open(); 

       SqlDataReader dr = sqlcommandStart.ExecuteReader(); 

       if (dr.HasRows) 
       { 
        while (dr.Read()) 
        { 
         Stringannounce = dr["AnnounceID"].ToString(); 
         announceID = Convert.ToDouble(Stringannounce); 


         SqlDataAdapter da = new SqlDataAdapter("SELECT TOP 1 id, qdate, ticket_number, QueueID, received, displaynum, station, transcodevoiced FROM vwAnnounce WHERE QueueID = @QueueID ORDER by received ASC", connStr); 
         //da.SelectCommand.CommandType = CommandType.StoredProcedure; 

         DataSet ds = new DataSet(); 
    *****************da.SelectCommand.Parameters.AddWithValue("@QueueID", comboBoxLocation.SelectedValue.ToString());***** //ERROR HERE 
         da.Fill(ds); 

         DataTable dt = new DataTable(); 
         dt = ds.Tables[0]; 


         foreach (DataRow dr2 in dt.Rows) 
         { 
          id = dr2["id"].ToString(); 
          announce = Convert.ToDouble(id); 
          ticketNum = dr2["ticket_number"].ToString(); 
          station = dr2["station"].ToString(); 
          //transcodevoiced = dr2["transcodevoiced"].ToString(); 
          displaynum = dr2["displaynum"].ToString(); 
          SplitString splitter = new SplitString(displaynum); 
          splitter.Split(); 

          if (announceID == announce) 
          { 
           // Set a value for the speaking rate. 
           reader.Rate = -4; 
           // Set the volume of the SpeechSynthesizer's ouput. 
           reader.Volume = 85; 
           //String that will be spoken 
           speak = "Now, " + displaynum + ", at #" + station; 

           //The problem with the Speak() function is that it is not threaded, so we use SpeakAsync(). It means that you cannot perform any other function in your windows form until the "reader" object has completed the speech. 
           reader.SpeakAsync(speak); 
           //Pauses system for 1 seconds after voice completion 
           Thread.Sleep(3000); 

           //Deletes record from Database table tblAnnounce 
           SqlCommand delete = new SqlCommand("DELETE FROM tblAnnounce WHERE AnnounceID = @announceID ", connStr); 
           delete.Parameters.AddWithValue("@announceID", announceID); 
           delete.ExecuteNonQuery(); 
           reader.Resume(); 
          } 
         }            
        } 
        connStr.Close(); 
       }      
       dr.Close(); 
      } 
     } 
    } 
    catch(Exception ex) 
    { 
     string exception = ex.Message; 
    } 
} 

Answer 1

理清你的问题，Invoke应该把以低于行：

comboBoxLocation.Invoke(
new Action(() => branch = comboBoxLocation.SelectedValue.ToString()); 

希望这有助于。

Answer 2

您正在通过窗体而不是控件调用。

使用此：

comboBoxLocation.Invoke(new MethodInvoker(delegate() 
{ 
    da.SelectCommand.Parameters.AddWithValue("@QueueID", comboBoxLocation.SelectedValue.ToString()); 
})); 

通过代替控制调用。

这是关于Microsoft线程安全调用的一个很好的资源。

http://msdn.microsoft.com/en-us/library/ms171728(v=vs.80).aspx

为了提高在你的代码，你也可以检查，看看是否需要调用或没有这样做之前。示例：

if (comboBoxLocation.InvokeRequired) 
{ 
    comboBoxLocation.Invoke(
      (MethodInvoker) 
       delegate { 
        da.SelectCommand.Parameters.AddWithValue("@QueueID", comboBoxLocation.SelectedValue.ToString()); 
}); 
else 
{ 
    da.SelectCommand.Parameters.AddWithValue("@QueueID", comboBoxLocation.SelectedValue.ToString()); 
}