Create Looper 的副业.md

blogs/Android/Framework/Interview/技巧心得相关/Looper 的副业.md

@@ -0,0 +1,26 @@
+---
+Looper 的副业
+---
+
+```c++
+int addFd(int fd, int ident, int events, sp<LooperCallback>& callback, ...){
+	epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, &eventItem);
+}
+void NativeMessageQueue::setFileDescriptorEvents(int fd, int events){
+    mLooper->addFd(fd, Looper::POLL_CALLBACK, looperEvents, this, reinterpret_cast<void*>(events));
+}
+void addOnFileDescriptorEventListener(FileDescriptor fd, int events, OnFileDescriptorEventListener listener){...}
+```
+
+Framework 里面有哪些地方用到了副业？
+
+```c++
+status_t NativeDisplayEventReceiver::initialize(){
+	mMessageQueue->getLooper()->addFd(mReceiver.getFd(), 0, EVENT_INPUT, this, NULL);
+}
+```
+
+#### 总结
+
+1. Looper 里可以监听其他描述符
+2. 创建管道，跨进程传数据，用 Looper 监听描述符事件