问题遇到的现象和发生背景
问题相关代码,请勿粘贴截图
private void SelectResultForm_Load(object sender, EventArgs e)
{
string sql = "select ca.id,c.name as coures_name,t.real_name as teacher_name,ca.course_time,ca.course_place,ca.max_num";
sql += " from course_arrange ca,course c, teacher t where ca.course_id = c.id and ca.teacher_id = t.id";
DataSet ds = SQLHelper.GetData(sql);
courseArrangeGridView.DataSource = ds.Tables[0];
int firstArrangeId = (int)ds.Tables[0].Rows[0][0];
sql = "select * from select_result where course_arrange_id" + firstArrangeId;
DataSet resultDs = SQLHelper.GetData(sql);
ResultGridView.DataSource = resultDs.Tables[0];//出错
}
private void courseArrangeGridView_CellContentClick(object sender, DataGridViewCellEventArgs e)
{
int selectId = (int)courseArrangeGridView.SelectedRows[0].Cells[0].Value;
string sql = "select * from select_result where course_arrange_id" + selectId;
DataSet resultDs = SQLHelper.GetData(sql);
ResultGridView.DataSource = resultDs.Tables[0];//出错
}
运行结果及报错内容
“System.NullReferenceException:未将对象引用设置到对象的实例“