黑马程序员学习日记----Close和Dispose区别

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简单的说：
    close:关闭以后还可以打开，
        Close()方法只是关闭了连接，然后这个连接被存储到连接池，所以在调用Close()方法以后，还是可以再通过

    dispose:直接销毁，不能再次利用！

   Close提供了一种即使在静态类中也能释放资源的方法（或者说约定）。而IDispose却只能用于非静态类或者说方法。
 由实现IDispose接口而生成的Dispose方法提供了一种简化代码编写的途径，如可以使用Using或者Foreach来释放。
Using在出了作用域后调用DIspose，SqlConnection.FileStream等内部都会做这样的判断：判断有没有close,如果
没有close就像dispose

 SqlConnection类的Dispose()方法是继承于Component类的，源代码是这样的：
        public void Dispose() { 
            Dispose(true); //调用Dispose的一个带参数的重载
            GC.SupPRessFinalize(this);  //请求系统不要调用指定对象的终结器。
        }
        protected virtual void Dispose(bool disposing) {
            if (disposing) { 
                lock(this) {
                    if (site != null && site.Container != null) {
                        site.Container.Remove(this);
                    } 
                    if (events != null) {
                        EventHandler handler = (EventHandler)events[EventDisposed]; 
                        if (handler != null) handler(this, EventArgs.Empty); 
                    }
                } 
            }
        }
SqlConnection类的Close()方法在MSDN中的说明是这样的：
关闭与数据库的连接。这是关闭任何打开连接的首选方法。 如果 SqlConnection 超出范围，则不会将其关闭。因
此，必须通过调用 Close 或 Dispose 显式关闭该连接。Close 和 Dispose 在功能上等效。如果连接池值 
Pooling 设置为 true 或 yes，则基础连接将返回到连接池。另一方面，如果 Pooling 设置为 false 或 no，则
会关闭到服务器的基础连接。 
看说明好象是Close()方法和Dispose()方法是类似的，实际上只是在关闭连接这个功能上等效，让我们看看Close
()方法的源代码：
        override public void Close() { 
            IntPtr hscp;
            Bid.ScopeEnter(out hscp, "<sc.SqlConnection.Close|API> %d#" , ObjectID);
            try {
                SqlStatistics statistics = null;

                RuntimeHelpers.PrepareConstrainedRegions(); 
                try {
#if DEBUG 
                    object initialReliabilitySlotValue = Thread.GetData(TdsParser.ReliabilitySlot); 

                    RuntimeHelpers.PrepareConstrainedRegions(); 
                    try {
                        Thread.SetData(TdsParser.ReliabilitySlot, true);
#endif //DEBUG
                        statistics = SqlStatistics.StartTimer(Statistics); 

                        // The lock here is to protect against the command.cancel / connection.close 

race condition 
                        // The SqlInternalConnectionTds is set to OpenBusy during close, once this 

happens the cast below will fail and 
                        // the command will no longer be cancelable.  It might be desirable to be 

able to cancel the close opperation, but this is
                        // outside of the scope of Whidbey RTM.  See (SqlCommand::Cancel) for other 

lock. 
                        lock (InnerConnection) {
                            InnerConnection.CloseConnection(this, ConnectionFactory);
                        }
                        // does not require GC.KeepAlive(this) because of OnStateChange 

                        if (null != Statistics) { 
                            ADP.TimerCurrent(out _statistics._closeTimestamp); 
                        }
#if DEBUG 
                    }
                    finally {
                        Thread.SetData(TdsParser.ReliabilitySlot, initialReliabilitySlotValue);
                    } 
#endif //DEBUG
                } 
                catch (System.OutOfMemoryException e) { 
                    Abort(e);
                    throw; 
                }
                catch (System.StackOverflowException e) {
                    Abort(e);
                    throw; 
                }
                catch (System.Threading.ThreadAbortException e) { 
                    Abort(e); 
                    throw;
                } 
                finally {
                    SqlStatistics.StopTimer(statistics);
                }
            } 
            finally {
                SqlDebugContext  sdc = _sdc; 
                _sdc = null; 
                Bid.ScopeLeave(ref hscp);
                if (sdc != null) { 
                   sdc.Dispose();
                }
            }
        } 
可以看到Close()方法并没有调用Dispose()方法，虽然有一行sdc.Dispose();，但是这只是释放SqlDebugContext
实例，和SqlConnection.Dispose()方法没有关系！

  
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