這里，我們考慮一個問題，Android中的應(yīng)用是一個looper線程，沒有任務(wù)時就阻塞著，其他線程通過handler調(diào)用等方式向主線程looper發(fā)送任務(wù)，

如果點(diǎn)擊應(yīng)用上的按鈕，應(yīng)用是怎么及時響應(yīng)的呢，

是專門啟動了一個額外的線程去監(jiān)控input事件么？

這里直接給出答案，input事件傳送給了系統(tǒng)IMS，IMS通過inputchannel把input傳送給應(yīng)用，而應(yīng)用中的主線程looper監(jiān)控了inputchannel的fd，

這里看一下主線程looper是怎么實(shí)現(xiàn)的監(jiān)控inputchannel的fd。

在應(yīng)用創(chuàng)建的時候，會調(diào)用ViewRootImpl的serView方法，

frameworks/base/core/java/android/view/ViewRootImpl.java

setView

mInputEventReceiver = new?WindowInputEventReceiver(inputChannel,

Looper.myLooper());

這里傳入了主線程的looper給WindowInputEventReceiver

這個構(gòu)造方法，調(diào)用其父類的構(gòu)造

public?InputEventReceiver(InputChannel?inputChannel, Looper?looper) {

if?(inputChannel?== null) {

throw?new?IllegalArgumentException("inputChannel must not be null");

}

if?(looper?== null) {

throw?new?IllegalArgumentException("looper must not be null");

}

mInputChannel?= inputChannel;

mMessageQueue?= looper.getQueue();

mReceiverPtr?= nativeInit(new?WeakReference<InputEventReceiver>(this),

mInputChannel, mMessageQueue);

mCloseGuard.open("InputEventReceiver.dispose");

}

static?jlong?nativeInit(JNIEnv* env, jclass?clazz, jobject?receiverWeak,

jobject?inputChannelObj, jobject?messageQueueObj) {

std::shared_ptr<InputChannel> inputChannel?=

android_view_InputChannel_getInputChannel(env, inputChannelObj);

if?(inputChannel?==?nullptr) {

jniThrowRuntimeException(env, "InputChannel is not initialized.");

return?0;

}

sp<MessageQueue> messageQueue?= android_os_MessageQueue_getMessageQueue(env, messageQueueObj);

if?(messageQueue?==?nullptr) {

jniThrowRuntimeException(env, "MessageQueue is not initialized.");

return?0;

}

sp<NativeInputEventReceiver> receiver?= new?NativeInputEventReceiver(env,

receiverWeak, inputChannel, messageQueue);

status_t?status?= receiver->initialize();

其中，receiver->initialize();

調(diào)用到

status_t?NativeInputEventReceiver::initialize() {

setFdEvents(ALOOPER_EVENT_INPUT);

return?OK;

}

void?NativeInputEventReceiver::setFdEvents(int?events) {

if?(mFdEvents?!= events) {

mFdEvents?= events;

auto&& fd?= mInputConsumer.getChannel()->getFd();

if?(events) {

mMessageQueue->getLooper()->addFd(fd.get(), 0, events, this, nullptr);

} else?{

mMessageQueue->getLooper()->removeFd(fd.get());

}

}

這里，打不過就加入，把inputchannel的fd也加入到主線程looper的epool監(jiān)控之中。文章來源地址http://www.zghlxwxcb.cn/news/detail-816053.html

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