C＃錯誤'對象引用未設置爲對象的實例'

我已閱讀關於此問題的其他問題，但沒有看到我的代碼拋出此錯誤的位置或原因。我的代碼如下，如果任何人都可以看到我要去哪裏錯了。C＃錯誤'對象引用未設置爲對象的實例'

private void btnSignIn_Click(object sender, EventArgs e) 
    { 
     sqlConnectionNW.ConnectionString = "Data Source=" + server + ";Initial Catalog=Northwind;Integrated Security=True"; 
     try 
     { 
      sqlConnectionNW.Open(); 
      String enteredDate = cmbDay.SelectedItem.ToString() + "/" + cmbMonth.SelectedItem.ToString() + "/" + cmbYear.SelectedItem.ToString(); 

      if ((txtEmployeeID.TextLength != 0) && (enteredDate.Length != 0)) 
      { 
       int ID = Convert.ToInt32(txtEmployeeID.Text); 
       employeesBindingSource.Filter = "EmployeeID ='" + txtEmployeeID.Text + "'"; 
       String birthDate; 
       birthDate = dsEmployees.Employees.FindByEmployeeID(ID).BirthDate.ToShortDateString(); 

       if (employeesBindingSource.Count > 0) //GETS TO HERE AND THEN GOES TO CATCH EX 
       { 
        sqlConnectionNW.Close(); 
        if (enteredDate.ToString() == birthDate.ToString()) 
        { 
         frmMenu frmMainMenu = new frmMenu(); 
         frmMainMenu.server = server; 
         frmMainMenu.employeeID = txtEmployeeID.Text; 
         MessageBox.Show("Welcome to the Northwind Ordering System"); 
         this.Hide(); 
         frmMainMenu.Show(); 
        } 
        else 
        { 
         MessageBox.Show("The birth date you have entered is incorrect"); 
        } 
       } 
       else 
       { 
        MessageBox.Show("The Employee ID you have entered does not exist"); 
       } 
      } 
     } 
     catch (Exception ex) 
     { 
      MessageBox.Show(ex.Message); 
     } 
     sqlConnectionNW.Close(); 
    }

來源

2011-03-25 6TTW014

你可以發佈堆棧跟蹤嗎？你知道哪一行是拋出錯誤嗎？ – Andy 2011-03-25 01:16:52

@Jon，編譯器如何幫助找到運行時異常的原因？ – 2011-03-25 01:19:27

已編輯帖子以顯示發生錯誤的位置。 – 6TTW014 2011-03-25 01:21:25

管理解決這個問題。我改變了這一點：

if ((txtEmployeeID.TextLength != 0) && (enteredDate.Length != 0)) 
      { 

       int ID = Convert.ToInt32(txtEmployeeID.Text); 

       employeesBindingSource.Filter = "EmployeeID ='" + txtEmployeeID.Text + "'"; 

       String birthDate; 

       birthDate = dsEmployees.Employees.FindByEmployeeID(ID).BirthDate.ToShortDateString(); // FROM HERE 

       if (employeesBindingSource.Count != 0) 
       { 

        sqlConnectionNW.Close();

要這樣：

IF（（txtEmployeeID.TextLength = 0）& &（enteredDate.Length = 0）！） {

   int ID = Convert.ToInt32(txtEmployeeID.Text); 

       employeesBindingSource.Filter = "EmployeeID ='" + txtEmployeeID.Text + "'"; 

       String birthDate; 

       if (employeesBindingSource.Count != 0) 
       { 
        birthDate = dsEmployees.Employees.FindByEmployeeID(ID).BirthDate.ToShortDateString(); //TO HERE 

        sqlConnectionNW.Close();

這是隻是在if語句之後放置「birthDate = ...」的情況。

來源

2011-03-25 12:18:06 6TTW014

C＃錯誤'對象引用未設置爲對象的實例'

回答

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