ConnectionString属性尚未初始化。 Winforms C＃.net

Question

我正在向已经建立的Winforms应用程序添加新表单。

我的表单上有一个DataGridView，后面的代码中的相关方法调用我的dbAPI DataTable方法。 我用与dbAPI类中使用的其他代码完全相同的代码编写了该方法但由于某种原因它没有初始化连接字符串...

 public DataTable getMyTable()
    {
        //used for populating the DataGridView
        SqlCommand _com = new SqlCommand(string.Format("select * from tab.myTable where Country = 'Angola' "), _conn);
        _com.CommandTimeout = _command_timeout;

        DataSet _ds = new DataSet();
        SqlDataAdapter _adapt = new SqlDataAdapter();
        try
        {
            _adapt.SelectCommand = _com;
            int i = _adapt.Fill(_ds, "Asset_Transactions");
            if (_ds.Tables.Count > 0)
            {
                return _ds.Tables[0];
            }
            else
            {
                return makeErrorTable("GetMyTable", "No Table Returned for myTable");
            }
        }
        catch (Exception e)
        {
            return makeErrorTable("GetMyTable", e.Message);
        }
    }

_conn是一个SQLConnection对象。 我的连接字符串在app.config中...

  class dbAPI
{
    Utils _utils = new Utils();

    //this is the API between the Application Code and the LDB Database
    string _ldb_connection_string = (string)dii.Properties.Settings.Default.connLDB; //connection string but with only one \ in settings as it gets converted to \\
    int _command_timeout = Convert.ToInt32((string)dii.Properties.Settings.Default.commandTimeOut); //Command time out
    SqlConnection _conn = new SqlConnection();

    public dbAPI()
    {
        //constructor
    }

    #region --------------- Database Connectivity Section
    public string openLocalDatabaseConnection()
    {
        try
        {
            //try to create the connection
            _conn = new SqlConnection(_ldb_connection_string);
            _conn.Open();
        }
        catch (Exception e)
        {
            return string.Concat("Can't connect to LDB with '", e.Message, "'");
        }

        return ""; //success
    }
    public string closeLocalDatabaseConnection()
    {
        _conn.Close();
        _conn.Dispose();

        return "";
    }

我得到一个空的连接字符串和'ConnectionString属性尚未初始化'异常抛出。 我不明白，因为我在课堂上有很多其他方法没有问题。 有任何想法吗？

谢谢

Answer 1

在继续进行之前，必须先调用openLocalDatabaseConnection（）函数，以便正确地使用连接字符串初始化SqlConnection对象。

代码：

        public DataTable getMyTable()
        {           
            openLocalDatabaseConnection();
            //used for populating the DataGridView
            SqlCommand _com = new SqlCommand(string.Format("select * from tab.myTable where Country = 'Angola' "), _conn);
            _com.CommandTimeout = _command_timeout;

            DataSet _ds = new DataSet();
            SqlDataAdapter _adapt = new SqlDataAdapter();
            try
            {
                _adapt.SelectCommand = _com;
                int i = _adapt.Fill(_ds, "Asset_Transactions");
                if (_ds.Tables.Count > 0)
                {
                    return _ds.Tables[0];
                }
                else
                {
                    return makeErrorTable("GetMyTable", "No Table Returned for myTable");
                }
            }
            catch (Exception e)
            {
                return makeErrorTable("GetMyTable", e.Message);
            }
        }

Answer 2

例如，将一个应用程序配置文件添加到您的项目中（或者在您拥有的项目内）并放置它（当然是您放置的名称和连接字符串）：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <connectionStrings>
    <add name ="MyConnection" connectionString ="your connection string here"/>
  </connectionStrings>
</configuration>

然后在你的_ldb_connection_string中：

string _ldb_connection_string = ConfigurationManager.ConnectionStrings["MyConnection"].ConnectionString;