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Frequently Asked Questions

This page describes how to perform various functions using the Rhodes / RhoSync frameworks and RhoHub.

How do I write “Hello, world” in Rhodes?

Edit the app/index.erb to create some content:

<div class="toolbar">
  <h1 id="pageTitle">
    Small demo app

<ul id="home" selected="true" title="Hello">
  <li><a href="another.erb">Hello, world which links to another page</a></li>

How do I add an OK button to my app?

The generated code from running (rhodes model <modelname> <attributelist>) contains several samples. Here’s a smaller fragment.

<form method="POST" action="<%= url_for(:action =>:update) %>">
<input type="submit" value="OK"/>

How do I insert a picture icon next to an element?

Adding to the above example:

<ul id="home" selected="true" title="Hello">
  <li><a href="another.erb"><img src="/public/images/bluebutton.png"></a></li>

How do I call a web service and process the returned data?

This is done with AsyncHttp. You will then use either JSON (if its a JSON web service) or REXML (if the web service returns XML) to process the data.

See the AsyncHttp example code which connects to an XML feed at and parses it with rexml.

How do I make a POST request to web service?

To make a POST request, use the AsyncHttp.post method. See the AsyncHttp.post docs here.

Can I process XML with Rhodes?

Yes, first add the following to your build.yml:

extensions: ["rexml", "set"]

Now parse the xml in your controller action:

require 'rexml/document'
file = File.new("bibliography.xml")
doc = REXML::Document.new(file)
puts doc

If you are planning to run your app on Blackberry, you should use the RhoXml extension. It has the same syntax as rexml, but has limited functionality and a much smaller memory footprint. Enable it in your application by adding to build.yml:

extensions: ["rhoxml"]

Now parse the xml in your controller action:

require 'rexml/document'
file = File.new("bibliography.xml")
doc = REXML::Document.new(file)
puts doc

If you have a very large XML document to parse, you should use the XML stream parser extension.

How can I seed a large amount of data into my application with Rhom?

You can either use the built-in Rhom functions or use a database transaction:

db = ::Rho::RHO.get_src_db('Model')
  items.each do |item|
    # create hash of attribute/value pairs
    data = {
      :field1 => item['value1'], 
      :field2 => item['value2'] 
    # Creates a new Model object and saves it
    new_item = Model.create(data)

If ::Rho::RHO.get_src_db(‘Model’) return nil, it means that you never call this models methods before(models are loaded by demand). To fix it call ‘require_source’:

require_source 'Model'  

How can I create a lot of objects in controller action?

When controller action is called Ruby Garbage Collector is disabled. If you create a lot of objects enable GC at the beginning of action:

def my_objects_generator
    #Do some heavy operations

To avoid UI block while controller action is performed, use AsyncHttp to make operation asynchronously (Local server will be blocked, but Html and JavaScript are not):

def start_objects_generator
    #callback has to be provided, otherwise operation will be synchronized
    AsyncHttp.get( :url => url_for(:action => do_objects_generation), :callback => (url_for :action => :generation_callback) )
    render page_with_progress_updated_by_javascript

def do_objects_generation
    #Do some heavy operations

    #do not call render here, call WebView.navigate or do it in  generation_callback      

def generation_callback
    WebView.navigate ( url_for :action => :show_results  )

How do I customize the app name and icons?

Follow the build section on setting the application name and icon.

How to improve application performance on Blackberry?

  • Before test application for performance set warning log level in rhoconfig.txt:

      MinSeverity = 3
  • Database is most critical part for performance improvement. See Database Performance Tips

  • If possible, do not use complex regular expressions – they slow works slow on Blackberry
  • If possible, do not use images in html body(single or tiled) – use solid color
  • If possible, do not use Exceptions to implement application logic. Add check for null parameters instead of catch Exception.
  • If possible, do not use Date/Time parse method. Use strptime instead. Use time as number when possible
  • Move require of big ruby files to methods when they used. This is true for locally used classes. Add system check for platform dependent code.
  • Exclude unused files from build(images, libraries etc). It will decrease application size and improve startup performance.Edit build.yml:
    - public/images/iphone
    - public/images/android
  • To parse XML use Stream parser: XML handling:XML Stream parser see – Rhodes Extensions

White screen between pages

It takes a bit of time for WebView to load and parse html/css of your page; meanwhile WebView show empty page which is white by default. Try setting default background color of the toolbar to the color of your pages:

Rho::NativeToolbar.create( :buttons => toolbar, 
    :background_color => 0x0000FF )

Please see more details about toolbar here

If you are loading JavaScript, consider doing it at the very end of your page; this way WebView will not wait for JS before parsing css and showing html.

How to pre-populate client database

  • Run application on target emulator, insert objects to database(locally or get data from server)
  • Copy all files from ‘db’ folder on emulator to ‘/platform\shared\db\res\db’. Here is how to find ‘db’ emulator folder:
    • iPhone: look inside log to find paths with guid – this is where application store files on emulator. Or run search by ‘syncdbuser.sqlite’ from disk root
    • Android: difficult since emulator is virtual machine and files stored inside emulator. Use adb command line to find path to application package
    • Windows Mobile: open device explorer from ActiveSync or ‘Mobile Device center’, navigate to ‘Program Files//rho/db’
    • Blackberry: open on computer file system – ‘/components/simulator/sdcard/Rho//db
  • Build application, now all db files are in the application package

How to remove toolbar from top-level index.erb

Edit app/application.rb file: initialize method

class AppApplication < Rho::RhoApplication

  def initialize
    #To remove default toolbar uncomment next line:
    #it should be before super
    @@toolbar = nil    


How to define controller for top-level index.erb

There is no way to define controller for top-level index.erb, so create special model and put index.erb there:

  • Create special ‘Home’ model
  • in rhoconfig.txt modify ‘start_path’ :

      start_path = '/app/Home'
  • ‘Home’ model index method:

      def index
          #do something

How to print document in Rhodes

  • Prepare file with printed content (html, pdf, image, etc.)
  • Open this file by


  • Print document from document application

How to use native Google map view on Android

  • Get Google Maps API key
  • Add ‘mapping’ and ‘apikey’ parameters to your build.yml

          mapping: yes
          apikey: <YOUR-API-KEY>
  • Add ‘network_state’ to capabilities list in your build.yml.

          - network_state

How to optimize memory usage in Rhodes

There are several Rhodes components which consume system memory( list order by memory consumptions, bigger first):

Internet Browser

Use system memory and a lot of graphics objects to display content. Rhodes Turn on Cache in Browser for static files like images, css, JavaScript etc

Tips to optimize Browser performance and memory consumption:

  • Use simple css and JavaScript frameworks
  • Do not display big lists with images on one page: use pagination

Ruby Virtual Machine

Use system memory. Here is the notes about RubyVM memory usage:

  • When application bundle creates ruby files compiled to internal format(iseq), so at runtime RubyVM work with precompiled files and do not perform ruby text parsing
  • RubyVM hold required Ruby files in memory. All required files keeps in memory till application exit
  • RubyVM allocate memory application objects. All global and class variables will remain in memory till you nil them
  • Controller object allocates/deallocates for each controller method request. So you cannot keep persistent information in Controller object
  • Ruby Garbage Collector works automatically. But to improve performance and stability GC is disabled before controller action and enabled after controller action exit. So if you allocate/deallocate a lot of Ruby objects in controller action: call GC.enable at the beginning.
  • Rhodes loads only framework ruby files at startup, all other libraries loads by demand including models

Tips to optimize RubyVM performance and memory consumption:

  • Load only required libraries
  • Do not load all ruby files at start: it will slow down application startup time. Load them by demand
  • Do not use big global or class variables. Keep persistent objects in database

Sqlite database

Use system memory. Here is the notes about Sqlite memory usage:

  • In some cases it may take more memory then Ruby VM : it depends of the database size.
  • Rhodes use unchanged Sqlite, so all documentation about Sqlite memory usage are correct for Rhodes Sqlite database.
  • Here is the database performance tips

Native controls like TabBar, Toolbar, Map etc

Use System memory and graphics objects.

Tips to optimize Native Controls performance and memory consumption:

  • Use low resolution camera images
  • Do not put large amount of pins to one map view
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