本文介绍了连接属性中的对象引用是否为空?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
OleDbConnection cn; public ExpireProduct() { InitializeComponent(); cn = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\MIS SYSTEM\AniPharmic\AniPharmic\MedicalDb.accdb;Jet OLEDB:Database Password=****"); } try { con.Open(); str = "select *from DatabaseLogin where user_id='" + textBox2.Text + "'"; com = new OleDbCommand(str, con); OleDbDataReader reader = com.ExecuteReader(); while (reader.Read()) { checkedListBox1.Items.Add(reader["stckdemge"]); } } catch (Exception ex) { MessageBox.Show(" " + ex); }
错误在第4行 -
Error is In this Line 4 -
con.Open();错误是: - 无法打开连接:System.NullReferenceException:Object Reference Not 设置为对象的实例。
推荐答案您已声明 cn 声明连接对象时。 使用它时,你写了 con 。将其更改为 cn 并查看错误是否仍然存在。 You have declared cn while declaring the connection object. While using it, you have written con. Change it to cn and see if the error is still there.
因为声明了 cn 所以你应该写 cn.open() 写这个... because declared cn so you should write cn.open() write this... try { cn.Open(); str = "select *from DatabaseLogin where user_id='" + textBox2.Text + "'"; com = new OleDbCommand(str, cn); OleDbDataReader reader = com.ExecuteReader(); while (reader.Read()) { checkedListBox1.Items.Add(reader["stckdemge"]); } } catch (Exception ex) { MessageBox.Show(" " + ex); }
快乐编码! :)
Happy Coding! :)
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连接属性中的对象引用是否为空?
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