最典型的android项目框架，如微信，陌陌，淘宝等大型项目都是类似此结构，本例实现其底部的菜单导航，是初学者最好的资料，简单易懂！-The most typical android fr a mework of the project, such as the micro-channel, street street, Taobao and other large projects are similar to this struct