需求
最近公司來了一個需求，需要將touch事件轉成key事件，只針對滑動事件與觸摸事件。
需求分析
首先這個需求是可以在kernel裏面做的，由於我們沒有kernel代碼，因此這個方案就被pass掉了。第二個想到的是在java層做，想找一個攔截touch事件的方法，類似PhoneWindowMananger中攔截key事件的方法，可是沒找到，找到的地方都已經到app層了，這樣就可能有點晚了（也可能java層有，只是我還沒找到合適的地方）。最後沒辦法將android事件分發機制重新看了一遍，決定直接在native層做，也就是讀取event的地方----InputReader.cpp中。
具體實現
這個需求裏面最重要的就是找到合適的地方攔截touch然後轉成key。
touch事件分發的函數：
void TouchInputMapper::dispatchMotion(nsecs_t when, uint32_t policyFlags, uint32_t source,
int32_t action, int32_t actionButton, int32_t flags,
int32_t metaState, int32_t buttonState, int32_t edgeFlags,
const PointerProperties* properties, const PointerCoords* coords,
const uint32_t* idToIndex, BitSet32 idBits, int32_t changedId,
float xPrecision, float yPrecision, nsecs_t downTime) {
PointerCoords pointerCoords[MAX_POINTERS];
PointerProperties pointerProperties[MAX_POINTERS];
uint32_t pointerCount = 0;
while (!idBits.isEmpty()) {
uint32_t id = idBits.clearFirstMarkedBit();
uint32_t index = idToIndex[id];
pointerProperties[pointerCount].copyFrom(properties[index]);
pointerCoords[pointerCount].copyFrom(coords[index]);
if (changedId >= 0 && id == uint32_t(changedId)) {
action |= pointerCount << AMOTION_EVENT_ACTION_POINTER_INDEX_SHIFT;
}
pointerCount += 1;
}
ALOG_ASSERT(pointerCount != 0);
if (changedId >= 0 && pointerCount == 1) {
// Replace initial down and final up action.
// We can compare the action without masking off the changed pointer index
// because we know the index is 0.
if (action == AMOTION_EVENT_ACTION_POINTER_DOWN) {
action = AMOTION_EVENT_ACTION_DOWN;
} else if (action == AMOTION_EVENT_ACTION_POINTER_UP) {
action = AMOTION_EVENT_ACTION_UP;
} else {
// Can't happen.
ALOG_ASSERT(false);
}
}
NotifyMotionArgs args(when, getDeviceId(), source, policyFlags,
action, actionButton, flags, metaState, buttonState, edgeFlags,
mViewport.displayId, pointerCount, pointerProperties, pointerCoords,
xPrecision, yPrecision, downTime);
getListener()->notifyMotion(&args);
}可以看到dispatchMotion這個函數的最後，構建了一個NotifyMotionArgs，然後通過getListener()->notifyMotion(&args)函數分發，NotifyMotionArgs這個類構造函數中的參數就是touch事件的參數，比如eventTime（也就是when）、action、xy座標等等都是後面我們要用的。
InputReader.cpp中也有key事件的分發函數，我們可以利用這個函數來轉key事件：
void KeyboardInputMapper::processKey(nsecs_t when, bool down, int32_t scanCode,
int32_t usageCode) {
int32_t keyCode;
int32_t keyMetaState;
uint32_t policyFlags;
if (getEventHub()->mapKey(getDeviceId(), scanCode, usageCode, mMetaState,
&keyCode, &keyMetaState, &policyFlags)) {
keyCode = AKEYCODE_UNKNOWN;
keyMetaState = mMetaState;
policyFlags = 0;
}
if (down) {
// Rotate key codes according to orientation if needed.
if (mParameters.orientationAware && mParameters.hasAssociatedDisplay) {
keyCode = rotateKeyCode(keyCode, mOrientation);
}
// Add key down.
ssize_t keyDownIndex = findKeyDown(scanCode);
if (keyDownIndex >= 0) {
// key repeat, be sure to use same keycode as before in case of rotation
keyCode = mKeyDowns.itemAt(keyDownIndex).keyCode;
} else {
// key down
if ((policyFlags & POLICY_FLAG_VIRTUAL)
&& mContext->shouldDropVirtualKey(when,
getDevice(), keyCode, scanCode)) {
return;
}
if (policyFlags & POLICY_FLAG_GESTURE) {
mDevice->cancelTouch(when);
}
mKeyDowns.push();
KeyDown& keyDown = mKeyDowns.editTop();
keyDown.keyCode = keyCode;
keyDown.scanCode = scanCode;
}
mDownTime = when;
} else {
// Remove key down.
ssize_t keyDownIndex = findKeyDown(scanCode);
if (keyDownIndex >= 0) {
// key up, be sure to use same keycode as before in case of rotation
keyCode = mKeyDowns.itemAt(keyDownIndex).keyCode;
mKeyDowns.removeAt(size_t(keyDownIndex));
} else {
// key was not actually down
ALOGI("Dropping key up from device %s because the key was not down. "
"keyCode=%d, scanCode=%d",
getDeviceName().string(), keyCode, scanCode);
return;
}
}
if (updateMetaStateIfNeeded(keyCode, down)) {
// If global meta state changed send it along with the key.
// If it has not changed then we'll use what keymap gave us,
// since key replacement logic might temporarily reset a few
// meta bits for given key.
keyMetaState = mMetaState;
}
nsecs_t downTime = mDownTime;
// Key down on external an keyboard should wake the device.
// We don't do this for internal keyboards to prevent them from waking up in your pocket.
// For internal keyboards, the key layout file should specify the policy flags for
// each wake key individually.
// TODO: Use the input device configuration to control this behavior more finely.
if (down && getDevice()->isExternal()) {
policyFlags |= POLICY_FLAG_WAKE;
}
if (mParameters.handlesKeyRepeat) {
policyFlags |= POLICY_FLAG_DISABLE_KEY_REPEAT;
}
if (down && !isMetaKey(keyCode)) {
getContext()->fadePointer();
}
NotifyKeyArgs args(when, getDeviceId(), mSource, policyFlags,
down ? AKEY_EVENT_ACTION_DOWN : AKEY_EVENT_ACTION_UP,
AKEY_EVENT_FLAG_FROM_SYSTEM, keyCode, scanCode, keyMetaState, downTime);
getListener()->notifyKey(&args);
}函數的最後我們可以看到一個與touch事件類似的分發調用，getListener()->notifyKey(&args)。
補充：其實這個getListener就是InputDispatcher對象。
總結
找到這兩個地方，轉換的需求也就簡單了，就是在TouchInputMapper::dispatchMotion中攔截touch事件，然後構建一個NotifyKeyArgs對象，通過調用getListener()->notifyKey(&args)來轉發key事件。代碼涉及到公司私密的邏輯我就不貼出來了，大概就是根據滑動的座標轉成相應的鍵值再轉發key事件。