Android Framework层截获按键消息

代码位置：

frameworks/base/services/input/InputDispatcher.cpp

所在函数：

void InputDispatcher::notifyKey( const NotifyKeyArgs* args) {
#if DEBUG_INBOUND_EVENT_DETAILS
ALOGD( "notifyKey - eventTime=%lld, deviceId=%d, source=0x%x, policyFlags=0x%x, action=0x%x, "
"flags=0x%x, keyCode=0x%x, scanCode=0x%x, metaState=0x%x, downTime=%lld",
args->eventTime, args->deviceId, args->source, args->policyFlags,
args->action, args->flags, args->keyCode, args->scanCode,
args->metaState, args->downTime);
#endif
if (!validateKeyEvent(args->action)) {
return;
}

uint32_t policyFlags = args->policyFlags;
int32_t flags = args->flags;
int32_t metaState = args->metaState;
if ((policyFlags & POLICY_FLAG_VIRTUAL) || (flags & AKEY_EVENT_FLAG_VIRTUAL_HARD_KEY)) {
policyFlags |= POLICY_FLAG_VIRTUAL;
flags |= AKEY_EVENT_FLAG_VIRTUAL_HARD_KEY;
}
if (policyFlags & POLICY_FLAG_ALT) {
metaState |= AMETA_ALT_ON | AMETA_ALT_LEFT_ON;
}
if (policyFlags & POLICY_FLAG_ALT_GR) {
metaState |= AMETA_ALT_ON | AMETA_ALT_RIGHT_ON;
}
if (policyFlags & POLICY_FLAG_SHIFT) {
metaState |= AMETA_SHIFT_ON | AMETA_SHIFT_LEFT_ON;
}
if (policyFlags & POLICY_FLAG_CAPS_LOCK) {
metaState |= AMETA_CAPS_LOCK_ON;
}
if (policyFlags & POLICY_FLAG_FUNCTION) {
metaState |= AMETA_FUNCTION_ON;
}

policyFlags |= POLICY_FLAG_TRUSTED;

KeyEvent event;
event.initialize(args->deviceId, args->source, args->action,
flags, args->keyCode, args->scanCode, metaState, 0,
args->downTime, args->eventTime);

mPolicy->interceptKeyBeforeQueueing(&event, /*byref*/ policyFlags);

if (policyFlags & POLICY_FLAG_WOKE_HERE) {
flags |= AKEY_EVENT_FLAG_WOKE_HERE;
}

bool needWake;
{ // acquire lock
mLock.lock();

if (shouldSendKeyToInputFilterLocked(args)) {
mLock.unlock();

policyFlags |= POLICY_FLAG_FILTERED;
if (!mPolicy->filterInputEvent(&event, policyFlags)) {
return; // event was consumed by the filter
}

mLock.lock();
}

int32_t repeatCount = 0;
KeyEntry* newEntry = new KeyEntry(args->eventTime,
args->deviceId, args->source, policyFlags,
args->action, flags, args->keyCode, args->scanCode,
metaState, repeatCount, args->downTime);

needWake = enqueueInboundEventLocked(newEntry);
mLock.unlock();
} // release lock

if (needWake) {
mLooper->wake();
}
}

notifyKey这个函数是按键消息，包括鼠标，键盘，遥控器，游戏手柄，虚拟键值等等消息的中转站
所以，在这个函数里你可以截获任何的按键消息，如HOME键等等，可以说这个函数就是一个水龙头，具体要做什么，就看有什么需求了。