在应用程序会话中两次调用相同的查询方法时，我得到“DBCommandExcept”
作为一个实验，我决定在方法结束时处理连接对象，看看这是否是问题所在。
我不再得到 DBCommandExcept 错误消息，而是得到“连接字符串属性尚未初始化”。
IOW，目前有点像第 22 条军规。相关代码是：
string query = "SELECT Bla FROM Blah";
SqlCeCommand cmd = new SqlCeCommand(query);
cmd.CommandType = CommandType.Text;
SqlCeConnection conn = dbconn.GetConnection();
cmd.CommandType = CommandType.Text;//probably unnecessary
cmd.Connection = conn;
SqlCeDataReader myReader = cmd.ExecuteReader(CommandBehavior.SingleRow);
try
{
if (myReader.Read())
{
itemID = myReader.GetString(ITEMID_INDEX);
packSize = myReader.GetString(PACKSIZE_INDEX);
recordFound = true;
}
}
catch (Exception ex)
{
RRDR.LogMsgs.Append(string.Format("Exception in PopulateControlsIfVendorItemsFound(): {0}", ex.Message));
}
finally
{
myReader.Close();
//if (null != conn)
//{
// conn.Dispose();
//}
}
// Re: 上面注释掉的块：当它处于活动状态时，没有看到DBCommandExcept问题；但是，然后我得到“连接字符串属性尚未初始化”
我认为上面唯一的非 SQL-CE 标准位是 dbConn.GetConnection()。这是其中的一些代码：
SqlCeConnection objCon = null;
. . .
public SqlCeConnection GetConnection()
{
return objCon;
}
private DBConnection() // class constructor
{
try
{
. . .
objCon = new SqlCeConnection(conStr);
objCon.Open();
. . .
同样，在应用程序的一次运行期间，仅通过此方法第二次看到错误（任何一个，无论我“选择”拥有哪个） 。第一次工作正常。
更新
我添加了下面的代码，评论讲述了悲惨的故事：
// With conn check only, still get two consecutive DBCommandExcepts
// With cmd check only, still get two consecutive DBCommandExcepts
// With both, still get two consecutive DBCommandExcepts; IOW, all have the same effect
if (null != conn)
{
conn.Close();
}
if (null != cmd)
{
cmd.Dispose();
}
更新 2
根据 unicron 的建议，我尝试使用“使用”。
在这三种情况中的两种（SqlCeCommand 和 SqlCeDataReader）中，转换为“使用”没有差异；在另一个（SqlCeConnection）中，它引发了错误消息，“ ConnectionString 属性尚未初始化。 ”
尽管如此，这两种用法的代码还是更简洁，因此感谢您在最佳实践方向上的推动。
这是它现在的样子：
private bool PopulateControlsIfPlatypusItemsFound()
{
const int ITEMID_INDEX = 0;
const int PACKSIZE_INDEX = 1;
bool recordFound = false;
try
{
string PlatypusId = txtPlatypus.Text.ToString().Trim();
string PlatypusItemId = txtUPC.Text.ToString().Trim();
string itemID = string.Empty;
string packSize = string.Empty;
string query = string.Format("SELECT ItemID, PackSize FROM PlatypusItems WHERE PlatypusID = {0} AND PlatypusItemID = {1}", PlatypusId, PlatypusItemId);
using (SqlCeCommand cmd = new SqlCeCommand(query))
{
cmd.CommandType = CommandType.Text;
SqlCeConnection conn = dbconn.GetConnection();
if ((null != conn) && (!conn.State.Equals(ConnectionState.Open)))
{
conn.Open();
TTBT.LogMsgs.Append("Connection opened");
}
cmd.CommandType = CommandType.Text;//probably unnecessary
cmd.Connection = conn;
using (SqlCeDataReader myReader = cmd.ExecuteReader(CommandBehavior.SingleRow))
{
if (myReader.Read())
{
itemID = myReader.GetString(ITEMID_INDEX);
packSize = myReader.GetString(PACKSIZE_INDEX);
recordFound = true;
}
}
txtID.Text = itemID;
txtSize.Text = packSize;
return recordFound;
}
}
catch (Exception ex)
{
TTBT.LogMsgs.Append(string.Format("Exception in PopulateControlsIfPlatypusItemsFound: {0} - {1}\r\n", ex.Message, ex.InnerException));
return recordFound;
}
}
更新 3
通过用通用排序替换自定义连接代码，我已经更接近常态，添加另一个“使用”到组合中：
private bool PopulateControlsIfVendorItemsFound()
{
const int ITEMID_INDEX = 0;
const int PACKSIZE_INDEX = 1;
bool recordFound = false;
DUCKBILL.LogMsgs.Append("Made it into frmEntry.PopulateControlsIfVendorItemsFound()\r\n");
try
{
string vendorId = txtVendor.Text.ToString().Trim();
string vendorItemId = txtUPC.Text.ToString().Trim();
string itemID = string.Empty;
string packSize = string.Empty;
if ( dbconn.isValidTable( "VendorItems" ) == -1 )
{
DUCKBILL.LogMsgs.Append("VendorItems not a valid table");//do not see this msg; good! VendorItems is seen as valid...
return false;
}
string query = string.Format("SELECT ItemID, PackSize FROM VendorItems WHERE VendorID = {0} AND VendorItemID = {1}", vendorId, vendorItemId);
using (SqlCeCommand cmd = new SqlCeCommand(query))
{
cmd.CommandType = CommandType.Text;
using (SqlCeConnection conn = new SqlCeConnection())
{
string filename = "\\badPlace2B\\CCRDB.SDF";
conn.ConnectionString = string.Format("Data Source = {0}", filename);
cmd.CommandType = CommandType.Text;//probably unnecessary/moot
cmd.Connection = conn;
conn.Open();
using (SqlCeDataReader myReader = cmd.ExecuteReader(CommandBehavior.SingleRow))
{
if (myReader.Read())
{
itemID = myReader.GetString(ITEMID_INDEX);
packSize = myReader.GetString(PACKSIZE_INDEX);
recordFound = true;
}
}
}
txtID.Text = itemID;
txtSize.Text = packSize;
return recordFound;
}
}
catch (Exception ex)
{
DUCKBILL.LogMsgs.Append(string.Format("Exception in PopulateControlsIfVendorItemsFound: {0} - {1}\r\n", ex.Message, ex.InnerException));
return recordFound;
}
}
...但我仍然得到“DBCommandExcept”...
至于“停止打开连接”，是不是必须这样做？上面的代码怎么可能/应该有所不同？
更新 4
更奇怪的是，现在我的调试日志文件已经停止写入了。我一直在全局异常处理程序和主窗体的 Closed event() 中写出它，并且它总是（直到现在）至少有几个条目，但在代码的最后几次更新中，它不是写多了……？？？
两个地方都是全局异常处理程序和主窗体的 Closed event()，代码是这样的：
public static bool inDebugMode = true;
. . .
if (CCR.inDebugMode)
{
DateTime dt = DateTime.Now;
string timeAsStr = string.Format("{0}_{1}_{2}_{3}.txt", dt.Hour, dt.Minute, dt.Second, dt.Millisecond);
using (StreamWriter file = new StreamWriter(timeAsStr))
{
// If the app closes normally, this is how the file is written; if it doesn't,
// (it crashed) it's written in PDAClient.ExceptionHandler()
file.WriteLine(SSCS.LogMsgs.ToString());
}
}
