C#杂乱知识汇总

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• - 我们在做http请求的时候如果想让返回的格式以json字符串返回: httpClient.DefaultRequestHeaders.Add("Accept","application/json;odata=verbose");

• HttpClient中有有参构造函数，其中的有参构造函数包括有参数HttpMessageHandler,该参数可以自定义逻辑实现

• VS2017快捷键:
  Ctrl+F12从任何基类型或基成员转到各种实现;  转到全部（Ctrl+T 或 Ctrl+,):直接转到任何文件/类型/成员/符号声明。可以使用此功能顶部的一排图标，以筛选结果列表或使用查询语法（例如，对文件使用“f searchTerm”、对类型使用“t searchTerm”等）.

• 事务处理
  <1>事务有事务管理器来管理和协调。每个影响事务结果的资源都由一个资源管理器来管理。事务管理器与资源管理器通信，以定义事务的结果。

  <2>ADO.NET事务不支持跨多个连接的事务，它总是关联到一个连接上的本地事务。

  <3>通过System.EnterpriseServices使用事务的优点是，不需要显式地进行事务处理，运行库会自动创建事务，只需要给有事务处理要求的类添加[Transaction]特性即可。[AutoComplete]特性把方法标记为自动设置事务的状态位:如果该方法成功，就设置成功位，因此可以提交事务，如果发生异常，就终止事务。使用System.EnterpriseServices创建事务的一大优点是，多个对象能轻松地运行在同一个事务中，事务还可以自动登记。缺点是它需要COM+主机模型，使用这个技术的类必须派生自基类ServiceComponent

  <4>System.Transactions
  CommittableTransaction是唯一一个支持提交的事务类，这个类有一个Commit方法，所有其他事务类都只能执行回滚。DependentTransaction类用于依赖于其他事务的事务，依赖的事务可以依赖从可提交的事务中创建的事务。

  System.Transactions支持可升级的事务处理，当多个SqlServer数据库连接添加到事务中时，就会进行这种升级，事务开始时是一个本地事务，之后升级为分布式事务。事务的升级需要启动分布式事务协调器(DTC)。如果在系统中升级事务时失败，就应验证DTC服务是否启动，

  System.Transactions的一大优点是环境事务，就不需要手动用连接登记事务，在支持环境事务的资源中，这是自动实现的。

  创建环境事务的一种方式是创建一个CommittableTransaction对象，把它赋予Transaction.Current属性，以初始化环境事务。初始化环境事务的另一种方式是使用TransactionScope类，TransactionScope类的构造函数会创建一个环境事务。

  要在另一个线程中使用同一个环境事务，就需要使用依赖事务。