20101022被面试的一些题（.net）

1, foreach 遍历需要实现什么接口?

该类型需要实现IEnumerable 或者 定义GetEnumerator 方法.

 

2，打印1到100内的素数。 

int m, k, n = 0; for (m = 2; m <100; m ++) { for (k = 2; k < m; k++) if (m % k == 0) break; if (k >= m) { Console.WriteLine("{0}", m); if (++n % 10 == 0) Console.WriteLine("/n"); } }

 

 3，接口能不能继承接口？抽象类能不能实现接口。抽象类能不能继承实体类？

An interface itself can inherit from multiple interfaces.一个接口自身可以继承多个接口。

Interfaces describe a group of related functionalities that can belong to any class or struct. 接口可以被任何类或结构体实现。

 

另外：

An interface is like an abstract base class: any non-abstract type that implements the interface must implement all its members.
An interface cannot be instantiated directly.
Interfaces can contain events, indexers, methods, and properties.
Interfaces contain no implementation of methods.
Classes and structs can implement more than one interface.
An interface itself can inherit from multiple interfaces.

 

4，解释partial关键字。

 partial 类型可以使我们把对某个类，结构体，接口或方法的描述写在不同地方，甚至写到两个或多个不同的文件中去。

 

5，垃圾回收机制。

当你想让类的使用者指定什么时候释放对象占用的资源时，你需要实现IDisposable 接口，或重写Dispose()方法。

 

6，页面的生命周期。

下面的Table列出方法，以及该方法总是active还是仅仅在PostBack时active。

方法	Active
Constructor	Always
Construct	Always
TestDeviceFilter	Always
AddParsedSubObject	Always
DeterminePostBackMode	Always
OnPreInit	Always
LoadPersonalizationData	Always
InitializeThemes	Always
OnInit	Always
ApplyControlSkin	Always
ApplyPersonalization	Always
OnInitComplete	Always
LoadPageStateFromPersistenceMedium	PostBack
LoadControlState	PostBack
LoadViewState	PostBack
ProcessPostData1	PostBack
OnPreLoad	Always
OnLoad	Always
ProcessPostData2	PostBack
RaiseChangedEvents	PostBack
RaisePostBackEvent	PostBack
OnLoadComplete	Always
OnPreRender	Always
OnPreRenderComplete	Always
SavePersonalizationData	Always
SaveControlState	Always
SaveViewState	Always
SavePageStateToPersistenceMedium	Always
Render	Always
OnUnload	Always

7， MVC各指什么？及其相互关系。

MVC是三个单词的缩写,分别为： 模型(Model),视图(View)和控制Controller)。Model层实现系统中的业务逻辑。 View层用于与用户的交互。 Controller层是Model与View之间沟通的桥梁，它可以分派用户的请求并选择恰当的视图以用于显示，同时它也可以解释用户的输入并将它们映射为模型层可执行的操作。

 

8, 说说c#中的static关键字。

常量或类型声明隐式的为static成员。

声明为static的成员不能通过实例来引用，需要通过类型名来引用。

 

9，事务。

using (OleDbConnection connection = new OleDbConnection(connectionString)) { OleDbCommand command = new OleDbCommand(); OleDbTransaction transaction = null; // Set the Connection to the new OleDbConnection. command.Connection = connection; // Open the connection and execute the transaction. try { connection.Open(); // Start a local transaction with ReadCommitted isolation level. transaction = connection.BeginTransaction(IsolationLevel.ReadCommitted); // Assign transaction object for a pending local transaction. command.Connection = connection; command.Transaction = transaction; // Execute the commands. command.CommandText = "Insert into Region (RegionID, RegionDescription) VALUES (100, 'Description')"; command.ExecuteNonQuery(); command.CommandText = "Insert into Region (RegionID, RegionDescription) VALUES (101, 'Description')"; command.ExecuteNonQuery(); // Commit the transaction. transaction.Commit(); Console.WriteLine("Both records are written to database."); } catch (Exception ex) { Console.WriteLine(ex.Message); try { // Attempt to roll back the transaction. transaction.Rollback(); } catch { // Do nothing here; transaction is not active. } } // The connection is automatically closed when the // code exits the using block. }

 

10， ViewState的作用。

ViewState是一种asp.net页面的Form postback时保持状态变化的一种技术。页面的viewstate默认的保存在一个叫_VIEWSTATE的隐藏form field中。