Rhino模拟记录回放语法有趣地使用了using。

using关键字定义对象的作用域，然后在作用域完成时释放对象。为例。

using (Font font2 = new Font("Arial", 10.0f))
{
    // Use font2
}

请参阅这里关于c#使用关键字的MSDN文章。

在c#中using关键字有以下两种用法。

As a directive Generally we use the using keyword to add namespaces in code-behind and class files. Then it makes available all the classes, interfaces and abstract classes and their methods and properties in the current page. Example: using System.IO; As a statement This is another way to use the using keyword in C#. It plays a vital role in improving performance in garbage collection. The using statement ensures that Dispose() is called even if an exception occurs when you are creating objects and calling methods, properties and so on. Dispose() is a method that is present in the IDisposable interface that helps to implement custom garbage collection. In other words if I am doing some database operation (Insert, Update, Delete) but somehow an exception occurs then here the using statement closes the connection automatically. No need to call the connection Close() method explicitly. Another important factor is that it helps in Connection Pooling. Connection Pooling in .NET helps to eliminate the closing of a database connection multiple times. It sends the connection object to a pool for future use (next database call). The next time a database connection is called from your application the connection pool fetches the objects available in the pool. So it helps to improve the performance of the application. So when we use the using statement the controller sends the object to the connection pool automatically, there is no need to call the Close() and Dispose() methods explicitly. You can do the same as what the using statement is doing by using try-catch block and call the Dispose() inside the finally block explicitly. But the using statement does the calls automatically to make the code cleaner and more elegant. Within the using block, the object is read-only and cannot be modified or reassigned. Example: string connString = "Data Source=localhost;Integrated Security=SSPI;Initial Catalog=Northwind;"; using (SqlConnection conn = new SqlConnection(connString)) { SqlCommand cmd = conn.CreateCommand(); cmd.CommandText = "SELECT CustomerId, CompanyName FROM Customers"; conn.Open(); using (SqlDataReader dr = cmd.ExecuteReader()) { while (dr.Read()) Console.WriteLine("{0}\t{1}", dr.GetString(0), dr.GetString(1)); } }

在前面的代码中，我没有关闭任何连接;它会自动关闭。由于using语句(using (SqlConnection conn = new SqlConnection(connString))， using语句将自动调用conn. close()，对于SqlDataReader对象也是如此。并且如果发生任何异常，它将自动关闭连接。

有关更多信息，请参见在c#中使用的用法和重要性。

using的另一个重要用途是实例化一个模态对话框。

Using frm as new Form1

    Form1.ShowDialog

    ' Do stuff here

End Using

using可以用来调用IDisposable。它还可以用于别名类型。

using (SqlConnection cnn = new SqlConnection()) { /* Code */}
using f1 = System.Windows.Forms.Form;

Interestingly, you can also use the using/IDisposable pattern for other interesting things (such as the other point of the way that Rhino Mocks uses it). Basically, you can take advantage of the fact that the compiler will always call .Dispose on the "used" object. If you have something that needs to happen after a certain operation ... something that has a definite start and end ... then you can simply make an IDisposable class that starts the operation in the constructor, and then finishes in the Dispose method.

这允许您使用非常好的使用语法来指示所述操作的显式开始和结束。这也是系统如何。事务处理可以工作。