這裏是我的代碼對象引用未設置到對象的實例在SQL ExecuteScalar方法
public string teacherfromdepart()
{
string programme = null;
this.obj = null;
using(SqlConnection con = new SqlConnection())
{
con.ConnectionString = Databaseconnection.ConnectionString;
con.Open();
using(SqlCommand cmd = new SqlCommand())
{
cmd.Connection = con;
cmd.CommandText = "Select [FID] FROM [NewFaculty] WHERE [FullName] =
'"+this.listBox1.Text+"'";
this.obj = cmd.ExecuteScalar();
cmd.CommandText = "SELECT [AssignedProgramme] FROM [Assignprogramme]" +
"WHERE ([FID] = '"+obj.ToString()+"')";
using(SqlDataReader dr = cmd.ExecuteReader())
{
while(dr.Read())
programme += dr["AssignedProgramme"].ToString() + ", ";
lblTeacherProgramme.Text = "This teacher Can teach " + programme;
return programme;
}
}
}
}
我正準備從數據庫系ID,並用它來獲取一些相關數據。 每當我關閉這個表格,並得到這個錯誤:http://prntscr.com/9y5jkr
沒有足夠的信息在這裏;什麼行引發異常?另外,使用參數。像這樣的查詢字符串是不好的,因爲SQL注入。 – Nikki9696
某些值爲空。在調試器中運行它並確定哪一個。或者看看發生錯誤的行,看看有什麼可能是空的。 –
http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it – Jens