Storyboard Lua Android Integration

On Android target platforms Storyboard provides an additional level of platform integration. In order to access the native Java service API on Android platforms Storyboard has incorporated the LuaJava module to provide a bridge from Storyboard Lua script functions to the Android Java API.

Access to the LuaJava bridge is through the luajava Lua variable. On non-Android platforms, this variable will not be defined and this can be used to provide alternate or simulated behavior.

    function my_callback(mapargs)
        if(luajava == nil) then
            print("LuaJava bridge not available")
            return
        end

        -- LuaJava available for use ...
    end

The general mapping of standard Lua/Java types such as strings and numbers is handled transparently so that Lua strings can be used in Java constructors and methods in the same way that the Java String class would normally be used and similarly for Lua numbers and vice/versa.

When a Lua variable is created that is a reference or proxy to a Java object, then access to the methods of that object are performed using the colon (:) notation with the Lua variable, lua_variable:method_name() notation. When accessing static member variables of an object, this can be performed using the traditional dot (.) notation lua_variable.member_variable_name. This is further demonstrated in the examples shown below.

In order to access a nested Java class for instantiation or binding, the dollar sign ($) must be used as a separator. For instance, if the Java class Bar is a nested class of Foo, then binding would work as follows: luajava.bindClass("Foo$Bar"). This is further demonstrated in the examples below.

A description of the complete Android Java API is beyond the scope of this document. For a complete coverage of the Android API refer to http://developer.android.com/reference/packages.html Depending on the functionality that your application is going to access, there may be additional restrictions that must be explicitly declared in the AndroidManifest.xml file. Permissions can be added in the Advanced Options section when exporting your Android project. The android:debuggable option has been changed to false by default. To change this, you will need to use your own custom manifest file. Export your manifest file to view it by clicking the Export button under the Manifest File tab. You can make changes to this file and then select it as a custom manifest file when exporting to ensure the manifest file is setup the way you want it to be.

Within the Android environment the Storyboard Engine execution takes place outside of the main Android/Java event loop. When integrating with the Android API's developers should always consider that they are using the Android API as if they were executing in a background thread and act accordingly. This may require the creation of additional Looper message event handlers if callback event handlers are being used. For more information on Android process model and multi-threading considerations, refer to the Android documentation: http://developer.android.com/guide/components/processes-and-threads.html.

Android Lua Java API

The mapping of Lua referenced objects to Android Java objects is relatively straightforward. All of the API functionality is accessed via the luajava Lua global variable. This variable provides four functions that can be used to access and manipulate standard Java objects and one variable that provides the Android Activity that is required.

luajava.newInstance(className, ...) This function creates a new Java object based on the fully qualified class name. Any additional parameters that are provided are passed through to the standard Java constructor.

The return value is a Lua variable that is a proxy to the Java object or nil if the class could not be instantiated.

    -- Create an instance of a Java string tokenizer
    local strTk = luajava.newInstance("java.util.
    StringTokenizer","a,b,c,d", ",")
    while strTk:hasMoreTokens() do
        print(strTk:nextToken())
    end

    -- Create a new Android Intent object (unpopulated)
    local intent = luajava.newInstance
    ("android.content.Intent")

luajava.bindClass(className) This function creates a reference to a Java class based on a fully qualified class name. This is different from newInstance() in that a new Java object is not created and the constructor is not invoked, but simply a reference to the class is returned. Use this when you need access to static fields or methods of a Java object.

The return value is a Lua variable that is a proxy to the Java Class object specified or nil if the class could not be found.

    -- Get the current system time
    local sys = luajava.bindClass("java.lang.System")
    print ( sys:currentTimeMillis() )

    -- Parse a string into an Android Uri
    local uriClass = luajava.bindClass("android.net.Uri")
    local phoneURI = uriClass:parse("tel:6135951999")

luajava.new(classObject, ....) This function is similar to the newInstance() function but rather than taking a fully qualified class name it takes an existing Class reference, generally obtained from calling bindClass(). Additional parameters can be passed to the Java constructor..

The return value is a Lua variable that is a proxy to the Java object or nil if the class could not be instantiated.

    -- Create a new string instance
    str = luajava.bindClass("java.lang.String")
    strInstance = luajava.new(str)

luajava.createProxy(interfaceNames, luaObject) If a Java API requires an interface to be implemented or provided as a set of callbacks, then it is where the createProxy() function can be used. The interfaceNames parameter is a comma separated list of fully qualified Java interfaces that will be implemented by the Lua variable luaObject. The names of the interface methods must be present in the luaObject variable.

The return value is a Lua variable that can be passed to any function or method that requires an implementation of that interface. If the creation of the proxy fails, then nil is returned.

    -- Create a Lua variable with the same interface as an ActionListener
    local button_cb = {}
    function button_cb.actionPerformed(ev)
        -- I would do something interesting here ...
    end

    -- Map the Lua variable to the Java interface
    buttonProxy = luajava.createProxy("java.awt.ActionListener", button_cb)

    -- Use the newly created interface instance on a Java object
    button = luajava.newInstance("java.awt.Button", "execute")
    button:addActionListener(buttonProxy)

luajava.nativeActivity() All significant interaction on an Android system involves working with an Activity (see http://developer.android.com/reference/android/app/Activity.html) Storyboard applications that are deployed to Android devices run as native activities which is a special class of the general Activity that allows those applications to interact directly with the graphics context and are generally C/C++ applications rather than pure Java applications.

The return value of this function is a Lua variable that is a proxy for the NativeActivity Java class used by this application or nil if the class could not be instantiated.

    -- Start an activity specified by a previously created Intent object
    local na = luajava.nativeActivity()
    if(na ~= nil) then
        na:startActivity(intent)
    else
        print("No Native Activity")
    end

Storyboard Lua Android Example

This example demonstrates how a phone call could be invoked as part of a Lua callback. In order for this example to work, the AndroidManifest.xml file must be changed to give permission for calls to be made: %<uses-permission android:name="android.permission.CALL_PHONE"></uses-permission>

     -- Log message routine to route diagnostic messages
    local function lm(msg)
        print(msg)
    end

    -- Call a selected phone number using the Android API
    -- Input is the string number value that is to be called
    local function call_phone_number(number)
        if(luajava == nil) then
            lm("No luajava Lua object")
            return
        end

        local na = luajava.nativeActivity()
        if(na == nil) then
            lm("No native activity available")
            return
        end

        local uriClass = luajava.bindClass("android.net.Uri")
        if(uriClass == nil) then
            lm("No java.lang.String object")
            return
        end

        local phoneURI = uriClass:parse("tel:" .. tostring(number))
        if(phoneURI == nil) then
            lm("No java.net.URI object")
            return
        end

        local intentClass = luajava.bindClass("android.content.Intent")
        if(intentClass == nil) then
            lm("No intent class")
            return
        end

        local intent = luajava.newInstance("android.content.Intent",
        intentClass.ACTION_CALL, phoneURI)
        if(intent == nil) then
            lm("No intent object")
            return
        end

        lm("Calling " .. number)
        na:startActivity(intent)
    end

This example demonstrates how to create a new instance of a nested inner class of a Java class. This example gets media metadata from the android.provider.MediaStore.Audio.Media class, which is a nested class of android.provider.MediaStore.Audio, which in turn is a nested class of android.provider.MediaStore.

    -- In order to pass array's to any of the Android Java API's we must explicitly create
    -- a Java array from a Lua table and this function covers that work.
    function make_array(dataClass, values)
        local arrayClass = luajava.bindClass("java.lang.reflect.Array")
        if(arrayClass == nil) then
            print("Can't get array class")
            return nil
        end

        local newTypedArray = arrayClass:newInstance(dataClass, #values)
        if(newTypedArray == nil) then
            print("Can't get array class")
            return nil
        end

        for i=1,#values do
            arrayClass:set(newTypedArray, i-1, values[i])
        end

        return newTypedArray
    end

    function get_album_files(album_id)
        if (luajava == nil) then
            return
        end

        if (luajava.bindClass == nil) then
            return
        end
        local na = luajava.nativeActivity()

        local mediastore = luajava.newInstance("android.provider.
        MediaStore$Audio$Media")
        local externalURI = mediastore.EXTERNAL_CONTENT_URI
        local columns = {}
        columns[1] = mediastore.TITLE_KEY
        columns[2] = mediastore.DURATION
        columns[3] = mediastore.TITLE

        local stringClass = luajava.bindClass("java.lang.String")
        local array = make_array(stringClass, columns)
        local where = mediastore.ALBUM_KEY .. "=?"
        local what = {}
        what[1] = album_id
        local whatArray = make_array(stringClass, what)

        local cursor = na:managedQuery(externalURI, array, where, whatArray, nil);
        local res = cursor_to_table(cursor)
        return res
    end