Handing local files


A RhoMobile application typically contains two different sets of files – one comprises the code for the application and another contains assets of different types: images, data files, etc.

Files that are only needed for rendering as-is in the WebView (such as images or stylesheets) can be placed anywhere within the public folder and referenced in your layout or view files as appropriate.

Data files required by the application at runtime must be accessed in two steps:

  • obtain the path to the file
  • process the information as required

You should always use the Application.*Folder properties and RhoFile.join to construct file paths because some platforms will not allow you to access files outside of your application bundle. In particular:

  • do not hardcode paths such as `/sdcard/*‘ even if your application only runs on Android
  • do not concatenate strings with \ or / characters manually in order to build paths with several components – use RhoFile.join instead

Reading other files bundled with your application

The Application API allows you to find where each part of your application is stored on the filesystem. Together with RhoFile.join this lets you construct paths to all relevant files of your app.


# Get the various app folders
appFolder = Rho::Application.appBundleFolder
appsBundleFolder = Rho::Application.appsBundleFolder
databaseBlobFolder = Rho::Application.databaseBlobFolder
publicFolder = Rho::Application.publicFolder
userFolder = Rho::Application.userFolder


// Get the various app folders
var appFolder = Rho.Application.appBundleFolder;
var appsBundleFolder = Rho.Application.appsBundleFolder;
var databaseBlobFolder = Rho.Application.databaseBlobFolder;
var publicFolder = Rho.Application.publicFolder;
var userFolder = Rho.Application.userFolder;

Each folder stores a particular type of content:

  • appBundleFolder points to your application’s app folder
  • appsBundleFolder is one level up from app
  • databaseBlobFolder is where database blobs are stored (i.e. images and other binary content)
  • publicFolder is your public folder, every file found here (or in a subfolder) can be accessed directly by WebView
  • userFolder is the only folder where you have write permissions. You are free to create or delete as many files as you need inside userFolder

Once you know where a file is stored, you can read it with the RhoFile API, which allows you to work with text files from both Ruby and JavaScript (note that binary files are not supported)


filename = Rho::RhoFile.join(Rho::Application.publicFolder, 'sample.txt') # build the path
contents = Rho::RhoFile.read(filename) # read the file into a variable


filename = Rho.RhoFile.join(Rho.Application.publicFolder, 'sample.txt') // build the path
contents = Rho.RhoFile.read(filename) // read the file into a variable

Saving files from the network to the device

the only directory you have write rights to is userFolder – other folders may work on some platforms but not others; in particular, iOS restricts writing files to any folder other than userFolder.

You can download files from an external server and store them on your device. The Network API lets your application download files using the Network.downloadFile method:


def download_file
  #Download a file to the specified filename.
  downloadfileProps = Hash.new
  downloadfileProps["filename"] = Rho::RhoFile.join(Rho::Application.userFolder, "sample.png")
  downloadfileProps["overwriteFile"] = true
  Rho::Network.downloadFile(downloadfileProps, url_for(:action => :download_file_callback))

def download_file_callback
    if @params["status"] == "ok"
            :message => "Download Success. File saved to " + Rho::RhoFile.join(Rho::Application.userFolder, "sample.png"),
            :buttons => ["OK"]
            :message => "Download Failed",
            :buttons => ["OK"]


function download_file_callback(params) {
    if (params["status"] == "ok") {
        alert("Download Succeeded. File saved to "+Rho.RhoFile.join(Rho.Application.userFolder, "sample.png"));
    } else {
        alert("Download Failed");

function download_file() {
    // Download a file to the specified filename. Be careful with the overwriteFile parameter!
    downloadfileProps = {
        url: "http://www.google.com/images/icons/product/chrome-48.png",
        filename: Rho.RhoFile.join(Rho.Application.userFolder, "sample.png"),
        overwriteFile: true
    Rho.Network.downloadFile(downloadfileProps, download_file_callback);

Exporting the database for backup purposes

The Database API allows your application to export the contents of the current database to a zip archive which you can then upload to a server, copy to a memory card or otherwise make available for the user to backup.


# open default database
db = Rho::Database.new(Rho::Application.databaseFilePath("user"),"user")
# export database
export_path = db.export
  :message => "Export path - #{export_path}",
  :buttons => ["OK"]


// open default database
var db = new Rho.Database(Rho.Application.databaseFilePath('user'), 'user');
// export database
var db = open_db();
var export_path = db.export();
alert("Export path - " + export_path);

Zipping and unzipping files

RhoMobile has built-in support for zip archives. The System API helps your application to zip or unzip any files. Make sure to observe the restriction that you should not be writing outside Application.userFolder.


# zip list of files
local_path_to_zip = Rho::RhoFile.join(Rho::Application.userFolder, "sample.zip")
local_path_to_file = Rho::RhoFile.join(Rho::Application.publicFolder, "sample.txt")
Rho::System.zipFile(local_path_to_zip, local_path_to_file)

# unzip a file 
local_path_to_zip = Rho::RhoFile.join(Rho::Application.userFolder, "sample.zip")


// zip list of files
var local_path_to_zip = Rho.RhoFile.join(Rho.Application.userFolder, "sample.zip");
var local_path_to_file = Rho.RhoFile.join(Rho.Application.publicFolder, "sample.txt");
Rho.System.zipFile(local_path_to_zip, local_path_to_file);

// unzip a file 
var local_path_to_zip = Rho.RhoFile.join(Rho.Application.userFolder, "sample.zip");
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