CoronaCards: Native/Lua Communication — Android

Overview

Communication between Lua and the Java environment is done through CoronaView instances which allow events to be sent from one environment to the other.

In Java, these events are represented by Hashtable instances. In Lua, they are basic Lua tables. Both follow the Corona convention for events with a required "name" key along with a string value that identifies the key. Further information can additionally be passed via a series of key-value pairs.

The central router for events between the two environments is the global Runtime object which exists on the Lua side.

Java to Lua

You can send events to Lua from Java by constructing a Corona-style event. In the example below, we create a custom event type ("pauseEvent") by instantiating an instance of HashMap. We fill this with the proper field (the key/value pair "name"/"pauseEvent") and a custom field "otherKey"/"otherValue". We then call the CoronaView method sendEvent, passing in the Hashtable. The CoronaView will automatically translate this to a Lua table and dispatch it to any Lua listener that has been registered with the global Runtime object.

// [Java]

CoronaView view = ...
Hashtable<Object, Object> event = new Hashtable<Object, Object>();
event.put("otherKey", "otherValue");
event.put("name", "pauseEvent");
view.sendEvent(event);

-- [Lua]

local function handlePause( event )

    if ( event.phase == "pause" ) then
        print( event.name ) --> pauseEvent
        print( event.otherKey ) --> otherValue
        --handle pause implementation here
    end
    return true
end

Runtime:addEventListener( "pauseEvent", handlePause )

Lua to Java

Lua code within a CoronaView instance can send events to the CoronaView. These events should be of the type coronaView and you must register a CoronaEventListener with setCoronaEventListener to listen for them. The Lua event table will be converted to a Hashtable by the time the listener is called.

// [Java]

coronaView.setCoronaEventListener(new CoronaEventListener() {
    @Override
    public Object onReceivedCoronaEvent(CoronaView view, Hashtable<Object, Object> event) {
        android.util.Log.i("Corona", event.get("message"));
        return "Nice to meet you CoronaCards!";
    }
});

-- [Lua]

local function pressMe( event )

    if ( event.phase == "ended" ) then
        local event = { name="coronaView", message="Hello from CoronaCards!" }
        -- Dispatch the event to the global Runtime object
        local result = Runtime:dispatchEvent( event )
        print( "Response: " .. result ) --> Response: Nice to meet you CoronaCards!
    end
    return true
end

local myObject:addEventListener( "touch", pressMe )