Communication between ArkTS and CPP

ArkTS-to-CPP

Sending a Message on ArkTS

On ArkTS, you can obtain the rnInstance instance and call rnInstance.postMessageToCpp(name: string, payload: any) to send a message to CPP. This method has two parameters:

• name: message name, which is used to distinguish different messages during broadcast.
• payload: message content to be sent.

this.ctx.rnInstance.postMessageToCpp("SAMPLE_MESSAGE", payload);

To send a message from ArkTS to Component or TurboModule, use any of the following methods to send a message to CPP:

Receiving a Message on CPP

• Method 1: Use onMessageReceived to receive a message.

  1. ComponentInstance needs to inherit ArkTSMessageHub::Observer to receive a message.

     class xxxComponentInstance
     : public CppComponentInstance<facebook::react::xxxShadowNode>,
       public ArkTSMessageHub::Observer
     

  2. Construct ArkTSMessageHub::Observer in the constructor.

     xxxComponentInstance::xxxComponentInstance(Context context)
         : CppComponentInstance(std::move(context)),
           ArkTSMessageHub::Observer(m_deps->arkTSMessageHub) {
             ···
     }
     

  3. Implement the onMessageReceived method in ComponentInstance to receive a message. After a message is received, determine whether to handle the message based on the message name.

     void xxxViewComponentInstance::onMessageReceived(
         ArkTSMessage const& message) {
       if (message.name == "SAMPLE_MESSAGE") {
         ···
       }
     }
     

• Method 2: Use handleArkTSMessage to receive a message.

  1. Create and implement the ArkTSMessageHandler class in Package, and implement the handleArkTSMessage method to handle the message.

     class SampleArkTSMessageHandler : public ArkTSMessageHandler {
       void handleArkTSMessage(const Context& ctx) override {
         ···
       };
     };
     

  2. Override the createArkTSMessageHandlers method of the Package object to return the ArkTSMessageHandler class.

     std::vector<ArkTSMessageHandler::Shared> SamplePackage::createArkTSMessageHandlers() {
       return {std::make_shared<SampleArkTSMessageHandler>()};
     }
     

CPP-to-ArkTS

Using postMessageToArkTS to Send a Message

1. Sending a message on CPP
   CPP uses the postMessageToArkTS method of the rnInstance object to send an event to ArkTS. This method has two parameters:

   • name: string, which is the name of the message to be sent.
   • payload: folly::dynamic, which is the data to be sent.

   m_deps->rnInstance.lock()->postMessageToArkTS(messageName, messagePayload);
   

2. Receiving a message on ArkTS
   On ArkTS, you can subscribe to the message sent from CPP by using cppEventEmitter in rnInstance and handle the message.

   const unsubscribe = rnInstance.cppEventEmitter.subscribe("SAMPLE_MESSAGE", (value: object) => {
     ···
     unsubscribe();
   })
   

Using TurboModule to Send a Message (Not Recommended)

1. Create TurboModule on ArkTS and implement the corresponding API.
2. CPP obtains the TurboModule object. On CPP, you can obtain the TurboModule object by using the getTurboModule method of the rnInstance object and convert this object to ArkTSTurboModule.

   auto TurboModule = m_deps->rnInstance.lock()->getTurboModule<xxxTurboModule>("moduleName");
   auto arkTsTurboModule = std::dynamic_pointer_cast<rnoh::ArkTSTurboModule>(turboModule);
   

3. Handle parameters and call the corresponding method on ArkTS.

   folly::dynamic payload = folly::dynamic::object;
   arkTsTurboMOudle->callSync(functionName, payload);