摘要:在CSDN论坛上看到下列问题，如果把DataReader当作DataGrid的DataSource，在DataGrid.DataBind()之后，在下列两种情形下，DataReader的IsClosed的值是不同的
1.IDataReader reader = SomeDBCommand.ExecuteReader();DataGrid1.DataSource = reader;DataGrid1.DataBind();
在这里，reader的IsClosed的值是false
2.IDataReader reader = SomeDBCommand.ExecuteReader(CommandBehavior.CloseConnection);DataGrid1.DataSource = reader;DataGrid1.DataBind();
在这里，reader的IsClosed的值是true
结论是，如果DataReader的CommandBehavior是CloseConnection的话，DataGrid1.DataBind()在某种(也许是非直接的)方式下，调用了DataReader的Close方法。在网上找到了一个类似的讨论，但他们没有给出原因。
把DataReader作为DataGrid的DataSource时，DataReader是当作IEnumerable来看待的，从IEnumerable可以获取IEnumerator，然后可以用它的MoveNext/Current来依次获取每个记录，难道MoveNext调用了DataReader的Close方法？做了个试验
using System;using System.Data;using System.Data.OleDb;using System.Data.SqlClient;using System.Collections;
class TestClose{ static void Main() { SqlConnection conn = new SqlConnection("server=localhost;database=pubs;uid=sa;pwd=;"); SqlCommand cmd = new SqlCommand("select * from authors", conn);
conn.Open(); SqlDataReader reader = cmd.ExecuteReader(CommandBehavior.CloseConnection); TestRead(reader); reader.Close();
conn.Open(); reader = cmd.ExecuteReader(CommandBehavior.CloseConnection); TestMoveNext(reader); reader.Close();
}
static void TestRead(IDataReader reader) { while (reader.Read()); Console.WriteLine("after Read(), reader is closed? {0}", reader.IsClosed); }
static void TestMoveNext(IDataReader reader) { IEnumerator e = ((IEnumerable)reader).GetEnumerator(); while (e.MoveNext()); Console.WriteLine("after MoveNext(), reader is closed?{0}", reader.IsClosed); }
}
输出是after Read(), reader is closed? Falseafter MoveNext(), reader is closed? True
果不其然啊，用Lutz Roeder的Reflector(大力推荐！)工具看了一下.NET里SqlDataReader的实现
IEnumerator System.Collections.IEnumerable.GetEnumerator(){ return new DbEnumerator(this, (CommandBehavior.Default != (CommandBehavior.CloseConnection & this._behavior)));}
可见SqlDataReader的CommandBehavior确实是传进去的，再看DbEnumerator的实现
public DbEnumerator(IDataReader reader, bool closeReader){ if (reader == null) { throw ADP.ArgumentNull("reader"); } this._reader......[
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