SurfaceComposerClient::Transaction& SurfaceComposerClient::Transaction::addTransactionCallback(
        TransactionCompletedCallbackTakesContext callback, void* callbackContext,
        CallbackId::Type callbackType) {
    auto listener = TransactionCompletedListener::getInstance();

    auto callbackWithContext = std::bind(callback, callbackContext, std::placeholders::_1,
                                         std::placeholders::_2, std::placeholders::_3);
    const auto& surfaceControls =
            mListenerCallbacks[TransactionCompletedListener::getIInstance()].surfaceControls;

    CallbackId callbackId =
            listener->addCallbackFunction(callbackWithContext, surfaceControls, callbackType);

    mListenerCallbacks[TransactionCompletedListener::getIInstance()].callbackIds.emplace(
            callbackId);
    return *this;
}

• TransactionCompletedCallbackTakesContext 是一个函数类型。

  using TransactionCompletedCallbackTakesContext =
          std::function<void(void* /*context*/, nsecs_t /*latchTime*/,
                             const sp<Fence>& /*presentFence*/,
                             const std::vector<SurfaceControlStats>& /*stats*/)>;
  

• 绑定 TransactionCompletedCallbackTakesContext 函数的第一个参数 callbackContext，这样其余 3 个参数正好和 TransactionCompletedCallback 函数一致。

  • TransactionCompletedCallback 是函数类型。

    using TransactionCompletedCallback =
            std::function<void(nsecs_t /*latchTime*/, const sp<Fence>& /*presentFence*/,
                               const std::vector<SurfaceControlStats>& /*stats*/)>;
    

• 如果是从 BLASTBufferQueue::acquireNextBufferLocked() 调用的，则 callbackContext 是 BLASTBufferQueue 指针。

• 用 TransactionCompletedListener::addCallbackFunction() 设置 surfaceControls、callbackType 和 callbackFunction，返回 CallbackId。

• 把新的 callbackId 写入 Transaction::mListenerCallbacks。

通过 Transaction::apply() 把 callback 传给 SurafceFlinger。