Class Overview 类简介
A Handler allows you to send and process Message and Runnable objects associated with a thread'sMessageQueue.
Handler允许你去发送和处理与thread的MessageQueue有关的Message和Runnable对象
Each Handler instance is associated with a single thread and that thread's message queue.
每一个Handler实例是与一个单独的thread和这个thread的message queue有关的
When you create a new Handler, it is bound to the thread / message queue of the thread that is creating it -- from that point on, it will deliver messages and runnables to that message queue and execute them as they come out of the message queue.
当你创建了一个新的Handler时，这个Handler一定会绑定一个thread或message queue。从那时起，Handler将会发送message和runnables到message queue，并且在它们从message queue中出来时，执行它们。
