1
我是新的C#開發,並嘗試創建一個簡單的應用程序,我遇到了一個問題。我想基於第一個ComboBox的SelectedIndexChanged屬性填充一個ComboBox。 Visual Studio在第二個cn.Open(在private void cboCities_SelectedIndexChanged)中聲明連接已經打開。但是,從我的代碼中我相信我已經關閉了它?我做錯了什麼?任何和所有的幫助是高度讚賞。謝謝!「連接已經打開(狀態=開)」
public partial class Form1 : Form
{
private SqlCeConnection cn = new SqlCeConnection(@"Data Source = \Program Files\ParkSurvey\ParkSurvey.sdf; Persist Security Info = False; Password = *");
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
cn.Open();
SqlCeCommand command = cn.CreateCommand();
command.CommandText = "SELECT Name FROM Cities ORDER BY Name ASC";
SqlCeDataAdapter da = new SqlCeDataAdapter(command);
DataSet ds = new DataSet();
da.Fill(ds);
cn.Close();
cboCities.ValueMember = "CityId";
cboCities.DisplayMember = "Name";
cboCities.DataSource = ds.Tables[0];
cboCities.SelectedIndex = -1;
}
private void cboCities_SelectedIndexChanged(object sender, EventArgs e)
{
if (cboCities.SelectedIndex > -1)
{
cn.Open();
string Cities = cboCities.SelectedValue.ToString();
SqlCeCommand command = cn.CreateCommand();
command.CommandText = "SELECT Name FROM Parks WHERE CityId ='" + Cities + "'";
SqlCeDataAdapter da = new SqlCeDataAdapter(command);
DataSet ds = new DataSet();
da.Fill(ds);
if (cn.State == ConnectionState.Open)
cn.Close();
cboParks.ValueMember = "ParkId";
cboParks.DisplayMember = "Name";
cboParks.DataSource = ds.Tables[0];
cboParks.SelectedIndex = -1;
}
}
}
你應該改變你的代碼以聲明每個方法一個新的連接,並在using語句包裹。然後它會自動關閉並處理。 – cadrell0 2012-04-27 19:25:22
如果您從「SelectedIndexChanged」中刪除打開的命令,它將不會拍攝任何內容?或者數據庫連接看起來像是打開的? – 2012-04-27 19:26:02
您正在嘗試複製ConnectionPool的工作。所以遵循@ cadrell0的建議:保持每個方法的本地連接。 – 2012-04-27 19:36:15