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我正在向已建立的 Winforms 应用程序添加新表单。

我的表单上有一个 DataGridView 和调用我的 dbAPI DataTable 方法的代码中的相关方法。我用与 dbAPI 类中使用的许多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，并抛出“ConnectionString 属性尚未初始化”异常。我不明白，因为我在课堂上还有许多其他方法可以正常工作。有任何想法吗？

谢谢

4

2 回答 2

2

在继续之前，您必须调用 openLocalDatabaseConnection() 函数，以便您的 SqlConnection 对象将正确地使用连接字符串初始化。

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);
            }
        }
于 2013-11-06T13:18:37.897 回答
0

例如，将应用程序配置文件添加到您的项目（或在您拥有的项目中）并放置（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>

然后在您的 _ldb_connection_string 中：

string _ldb_connection_string = ConfigurationManager.ConnectionStrings["MyConnection"].ConnectionString;
于 2013-11-06T13:33:43.920 回答