未将对象引用设置到对象的实例

Question

  public static class DBHelper
    {        private static SqlConnection connection;
        public static SqlConnection Connection
        {
            get 
            {
                string connectionString = ConfigurationManager.ConnectionStrings["MyOfficeConnectionString"].ConnectionString;//这句说是  未将对象引用设置到对象的实例。
              if (connection == null)
                {
                    connection = new SqlConnection(connectionString);
                    connection.Open();
                }
                else if (connection.State == System.Data.ConnectionState.Closed)
                {
                    connection.Open();
                }
                else if (connection.State == System.Data.ConnectionState.Broken)
                {
                    connection.Close();
                    connection.Open();
                }
                return connection;
            }
        }

Answer 1

看下web.config文件中有没有MyOfficeConnectionString的连接字符串配置项，或者你写到AppSettings中去了

Answer 2

web.config中没有找到MyOfficeConnectionString结点，所以
ConfigurationManager.ConnectionStrings["MyOfficeConnectionString"]这个对象是NULl类型的
获取其属性就会出错

Answer 3

保证这个project的debug目录下有web.config文件。
web.config 里面有MyOfficeConnectionString的连接字符串配置项

Answer 4

web.config文件中没有MyOfficeConnectionString

Answer 5

看看 MyOfficeConnectionString是不是在<connectionStrings>这个节点之下
再看看名字有没有弄错 最好是复制过来

Answer 6

web.config里面怎么写的
你应该这样写
<connectionStrings>
  <add name="MyOfficeConnectionString" connectionString="Data Source=.;Initial Catalog=数据库名称;Integrated Security=True"
   providerName="System.Data.SqlClient" />
 </connectionStrings>