Android handler messaging mechanism

When the worker thread sends a message to the main thread, because the main thread is looper, there is no need to initialize the Looper, pay attention to who sends the message to associate whose handler, this time uses is the main thread handler

Handler will send the message to the MessageQueue queue, Looper will continue to traverse the MessageQueue queue, when there is a message will be callback handler method Handlemessage!

When the main thread sends a message to a worker, the handler of the child thread is associated, and the child thread is not looper. So we need to call Looper.prepare (), initialize a looper, put in threadlocal,

Finally call the Looper.loop method to start polling the messages inside the MessageQueue queue, and the mechanism is the callback mechanism!

Android handler messaging mechanism