我没有关闭以前的DataReader，但在哪里？ [英] I didn't close previous DataReader, but where?
问题描述
我，所以我没有使用'使用'改变了我以前的代码。早前工作，并在不同的类代码基本上是同样的东西，但它的工作。
我它已经盯着2小时，现在，我只是想不通。哪里出了问题，可能是
我只有一个读者，但我使用DisplayFileContent方法，我得到的错误每次：错误：有已经使用此命令，必须先关闭相关联的打开的DataReader。
//可能市民这样我们就可以显示
//文件的不同形式的内容。
公共无效DisplayFileContent（字符串文件路径）
{
//计数所有条目。
INT countEntries = 0;
//加密/解密数据。
EncryptDecrypt安全=新EncryptDecrypt（）;使用（OleDbConnection的连接=新的OleDbConnection（））
{
connection.ConnectionString =
供应商= Microsoft.ACE.OLEDB.12.0; +
数据源=+文件路径+; +
持续安全信息=假; +
的Jet OLEDB：数据库密码=+
hashPhrase.ShortHash（storedAuth.Password）+;;使用
（OleDbCommand的命令=新的OleDbCommand
（SELECT * FROM PersonalData连接））
{
OleDbDataReader读取;
试
{
//打开数据库连接。
connection.Open（）;
//创建一个数据读取器。
读= Command.ExecuteReader却（）;
//继续之前清除文本框。
txtDisplay.Text =的String.Empty;
//检查是否存在的文件中的任何数据。
如果（read.HasRows）
{
//从文件读取信息。
而（read.Read（））
{
//计数从阅读器读取的所有条目。
countEntries ++;
//从文件中读取字符串的所有值。
//虽然每个字符串加密，我们必须解密。
//用户名和密码是一样的用户提供的
//同时验证。
txtDisplay.Text + ====条目ID：+ read.GetValue（0）+
===+ Environment.NewLine;
txtDisplay.Text + =类型：+ security.Decrypt
（read.GetString（1），storedAuth.Password，
storedAuth.UserName）+ Environment.NewLine; （！read.IsDBNull（2））
如果
txtDisplay.Text + =URL：+
security.Decrypt（read.GetString（2），
storedAuth.Password ，storedAuth.UserName）+
Environment.NewLine;
如果
txtDisplay.Text + =软件名称：（read.IsDBNull（3）！）+
security.Decrypt（read.GetString（3），
storedAuth。密码，storedAuth.UserName）+
Environment.NewLine;
如果
txtDisplay.Text + =串行代码：（read.IsDBNull（4）！）+
security.Decrypt（read.GetString（4），
storedAuth。密码，storedAuth.UserName）+
Environment.NewLine;
如果
txtDisplay.Text + =用户名：（read.IsDBNull（5）！）+
security.Decrypt（read.GetString（5），
storedAuth。密码，storedAuth.UserName）+
Environment.NewLine; （！read.IsDBNull（6））
如果
txtDisplay.Text + =密码：+
security.Decrypt（read.GetString（6），
storedAuth.Password ，storedAuth.UserName）+
Environment.NewLine;
txtDisplay.Text + = Environment.NewLine;
}
}
，否则
{
txtDisplay.Text =没有什么可显示！+
：你必须之前，所以我可以添加的东西这里显示任何内容。;
}
//显示在状态栏条目数。
tsslStatus.Text =共有+ countEntries +的条目。
//选择0字符以确保文本
//没有完全地选择。
txtDisplay.SelectionStart = 0;
command.ExecuteNonQuery（）;
}
赶上（异常前）
{
MessageBox.Show（错误：+ ex.Message）;
}
}
}
}
您只是catch块之前调用command.ExecuteNonQuery。你需要先关闭您的DataReader
我建议包装，利用在使用块DataReader的反正代码：
使用（OleDbDatareader读= Command.ExecuteReader却（））
{
：
}
正如上面所指出的，command.ExecuteNonQuery（）是执行命令，你不期望从返回结果。这些通常是插入，更新或删除，但也可能包括存储过程调用，这样做，或者你不关心返回的结果。
I have changed my previous code so I am not using 'using'. It work earlier, and code in different class basically represent the same thing, but its working.
I have stared at it for 2 hours now and I just can't figure out where the problems might be.
I have only one reader but each time I am using DisplayFileContent method I am getting the error: Error: There is already an open DataReader associated with this command which must be closed first.
// May be public so we can display
// content of file from different forms.
public void DisplayFileContent(string filePath)
{
// Counting all entries.
int countEntries = 0;
// Encrypting/Decrypting data.
EncryptDecrypt security = new EncryptDecrypt();
using (OleDbConnection connection = new OleDbConnection())
{
connection.ConnectionString =
"Provider=Microsoft.ACE.OLEDB.12.0;" +
"Data Source=" + filePath + ";" +
"Persist Security Info=False;" +
"Jet OLEDB:Database Password=" +
hashPhrase.ShortHash(storedAuth.Password) + ";";
using (OleDbCommand command = new OleDbCommand
("Select * FROM PersonalData", connection))
{
OleDbDataReader read;
try
{
// Open database connection.
connection.Open();
// Create a data reader.
read = command.ExecuteReader();
// Clearing the textbox before proceeding.
txtDisplay.Text = string.Empty;
// Checking if there is any data in the file.
if (read.HasRows)
{
// Reading information from the file.
while (read.Read())
{
// Count all entries read from the reader.
countEntries++;
// Reading all values from the file as string.
// While each string is encrypted, we must decrypt them.
// User name and password is the same as user provided
// while authentication.
txtDisplay.Text += "=== Entry ID: " + read.GetValue(0) +
" ===" + Environment.NewLine;
txtDisplay.Text += "Type: " + security.Decrypt
(read.GetString(1), storedAuth.Password,
storedAuth.UserName) + Environment.NewLine;
if (!read.IsDBNull(2))
txtDisplay.Text += "URL: " +
security.Decrypt(read.GetString(2),
storedAuth.Password, storedAuth.UserName) +
Environment.NewLine;
if (!read.IsDBNull(3))
txtDisplay.Text += "Software Name: " +
security.Decrypt(read.GetString(3),
storedAuth.Password, storedAuth.UserName) +
Environment.NewLine;
if (!read.IsDBNull(4))
txtDisplay.Text += "Serial Code: " +
security.Decrypt(read.GetString(4),
storedAuth.Password, storedAuth.UserName) +
Environment.NewLine;
if (!read.IsDBNull(5))
txtDisplay.Text += "User Name: " +
security.Decrypt(read.GetString(5),
storedAuth.Password, storedAuth.UserName) +
Environment.NewLine;
if (!read.IsDBNull(6))
txtDisplay.Text += "Password: " +
security.Decrypt(read.GetString(6),
storedAuth.Password, storedAuth.UserName) +
Environment.NewLine;
txtDisplay.Text += Environment.NewLine;
}
}
else
{
txtDisplay.Text = "There is nothing to display! " +
"You must add something before so I can display anything here.";
}
// Displaying number of entries in the status bar.
tsslStatus.Text = "A total of " + countEntries + " entries.";
// Selecting 0 character to make sure text
// isn't completly selected.
txtDisplay.SelectionStart = 0;
command.ExecuteNonQuery();
}
catch (Exception ex)
{
MessageBox.Show("Error: " + ex.Message);
}
}
}
}
You are calling command.ExecuteNonQuery just before the catch block. You'll need to close your DataReader first.
I'd recommend wrapping the code that utilizes the datareader in a using block anyway:
using(OleDbDatareader read = command.ExecuteReader())
{
...
}
As pointed out above, command.ExecuteNonQuery() is for executing commands that you don't expect a return result from. These typically are inserts, updates or deletes, but may also include stored proc calls that do the same, or where you don't care about the returned result
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