The Main Thread of Android sends messages to child threads

We normally send messages from the child thread to the main thread, and the main thread already does Looper for us by default, so we can simply “create a Handler object and one thread sends messages and the other receives messages”… Let’s start by saying what a Looper is. It is like a Looper of a MessageQueue. A Message queue has only one Looper and manages the entire Message queue. A Message queue can hold multiple messages and workers can have multiple handlers. The butler sends them to perform tasks after storing or retrieving messages to the message queue;

So the number of them is as follows: Looper: 1; MessageQueue (MessageQueue) : 1; Message: You can have more than one; Worker (Handler) : Can be multiple;

New Thread(new Runnable() {@suppressLint ("HandlerLeak") @override public void run() { Our main thread is sending messages to child threads, so we need to keep the child thread immortal /** * 1. The Looper object is created, and MessageQueue * 2 is created in the Looper object. ThreadLocal */ looper.prepare (); ThreadLocal */ looper.prepare (); SubHandler = new Handler(){@override public void handleMessage(@nonnull MSG){if (msg.what==2) { Toast.maketext (mainactivity.this, "main thread: "+ msg.obj.tostring (), toast.length_short).show(); }}}; mLooper = Looper.myLooper(); /** * 1. Find the previously created Looper object from the current thread and then find MessageQueue * 2. */ looper.loop (); */ looper.loop (); Log.d(TAG, "run: loop() finished "); } }).start();Copy the code

@override protected void onDestroy() {super.ondestroy (); if (mLooper! =null) { mLooper.quit(); }}Copy the code

Reference: blog.csdn.net/iblade/arti…