未将对象引用设置为对象的实例

Dim In_Total As Integer = 0 
    Dim Ph_Total As Integer = 0 

    Dim Day_In_Total As Integer = 0 
    Dim Day_Ph_Total As Integer = 0 
    Dim Course_Names1(1) As String 

    Qry = "SELECT DISTINCT Course_Name,Course_ID FROM Courses WHERE (Course_ID IN (SELECT Course_Id FROM Student_Courses_Pref WHERE student_Id IN (SELECT student_Id FROM Student_Info WHERE Inserted_date >= '" + Now.Month.ToString() + "-1-" + Now.Year.ToString() + "' and Inserted_date <= '" + Now.Date + "' and Branch_Code = '" + BName + "') and Branch_Code = '" + BName + "')) and Branch_Code = '" + BName + "' and Active = 'Y' order by Course_Id" 
    str = str + "<br> <br> <center><font face ='Verdana' size='+1'><B><U> Summary Report of " + MonthName(Now.Month()).ToString() + "," + Now.Year.ToString() + "</B></U> <br><br>" 
    com.CommandText = Qry 
    com.Connection = con 
    dr = com.ExecuteReader 

    str = str + "<table align='center' style='FONT-FAMILY: Verdana' bgcolor='#336699' width='100%'>" 
    str = str + "<tr style='FONT-WEIGHT: bold; FONT-SIZE: x-small;FONT-FAMILY: Verdana' bgColor='#b9ceee'><td align='center' width='3%'> Date </td>" 
    i = 0 

    While dr.Read 
     str = str + "<td align='Center' colspan='2' width='30%'>" + dr(0).ToString() + "</td>" 
     ReDim Preserve Course_Names1(i) 
     Course_Names1(i) = dr(1) 
     i = i + 1 
    End While 
    dr.Close() 
    str = str + "<td colspan ='2'>Total</td></tr>" 
    For i = 0 To Now.Day 
     If i = 1 Then 
      str = str + "<tr style='FONT-SIZE: x-small;FONT-FAMILY: Verdana' bgColor='#b9ceee'><td>" + i.ToString() + "<sup>st</sup>" + MonthName(Now.Month()).Substring(0, 3) + "</td>" 
     ElseIf i = 2 Then 
      str = str + "<tr style='FONT-SIZE: x-small;FONT-FAMILY: Verdana' bgColor='#b9ceee'><td>" + i.ToString() + "<sup>nd</sup>" + MonthName(Now.Month()).Substring(0, 3) + "</td>" 
     ElseIf i = 3 Then 
      str = str + "<tr style='FONT-SIZE: x-small;FONT-FAMILY: Verdana' bgColor='#b9ceee'><td>" + i.ToString() + "<sup>rd</sup>" + MonthName(Now.Month()).Substring(0, 3) + "</td>" 
     Else 
      str = str + "<tr style='FONT-SIZE: x-small;FONT-FAMILY: Verdana' bgColor='#b9ceee'><td>" + i.ToString() + "<sup>th</sup>" + MonthName(Now.Month()).Substring(0, 3) + "</td>" 
     End If 
     Qry = "" 
     For j = 0 To Course_Names1.Length - 1 'Here i got the error 
      Qry = "select count(student_id),enquiry_by from student_info where inserted_date = '" + MonthName(Now.Month).ToString() + " " + i.ToString() + "," + Now.Year.ToString() + "' and student_id in (select student_id from student_courses_pref where branch_code = '" + BName + "' and Course_id = '" + Course_Names1(j).ToString() + "') and branch_code ='" + BName + "' group by Enquiry_By " 
      com.CommandText = Qry 
      dr = com.ExecuteReader 
      While dr.Read() 
       If dr.HasRows Then 
        If UCase(dr(1).ToString()) = "I" Then 
         'str = str + "<td width='15%' bgcolor='#ffffff'>" + dr(0).ToString() + "</td><td width='15%' bgcolor='#c2ffc8'></td>" 
         In_Total += dr(0) 
        ElseIf UCase(dr(1).ToString()) = "P" Then 
         'str = str + "<td width='15%'bgcolor='#ffffff'></td><td width='15%' bgcolor='#c2ffc8'>" + dr(0).ToString() + "</td>" 
         Ph_Total += dr(0) 
        End If 
       Else 
        'str = str + "<td width='15%' bgcolor='#ffffff'></td><td width='15%' bgcolor='#c2ffc8'></td>" 
       End If 
      End While 
      If In_Total <> 0 Then 
       str = str + "<td width='15%' bgcolor='#ffffff'>" + In_Total.ToString() + "</td>" 
      Else 
       str = str + "<td width='15%' bgcolor='#ffffff'> </td>" 
      End If 

      If Ph_Total <> 0 Then 
       str = str + "<td width='15%' bgcolor='#c2ffc8'>" + Ph_Total.ToString() + "</td>" 
      Else 
       str = str + "<td width='15%' bgcolor='#c2ffc8'> </td>" 
      End If 
      dr.Close() 
      Day_In_Total += In_Total 
      Day_Ph_Total += Ph_Total 

      In_Total = 0 
      Ph_Total = 0 
     Next 
     str = str + "<td>" + Day_In_Total.ToString() + "</td><td>" + Day_Ph_Total.ToString() + "</td></tr>" 
     Day_In_Total = 0 
     Day_Ph_Total = 0 
    Next 
    str = str + "</tr></table>"

来源

2011-05-30 Naresh

这可能意味着j为null，或者Course_Names1为null，这是什么？ – 2011-05-30 10:25:30

哪里定义了str？是否用Dim str as string=""初始化？

str = str + "<br> <br>...

来源

2011-05-30 10:23:24

雅这是字符串 dim str as String =“” – Naresh 2011-05-30 11:17:27

未将对象引用设置为对象的实例

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