三层实例(C#) 其实三层理解起来很简单，就是把不同的责任划分到不同的层，以达到解耦的目的。分层的目的就是为了让程序变得高内聚、低耦合，使代码更加灵活、易扩展，让代码更具有易用性等等。-The three-tier instance (C#) is actually three layers to understand very simple, is divided into different responsibilities to different layers in order to a