Elevate

Stop scattering your domain logic across your view controller. Consolidate it to a single conceptual unit with Elevate.

Example

@login_task = async username: username.text, password: password.text do
  # This block runs on a background thread.
  task do
    # @username and @password correspond to the Hash keys provided to async.
    args = { username: @username, password: @password }

    credentials = Elevate::HTTP.post(LOGIN_URL, args)
    if credentials
      UserRegistration.store(credentials.username, credentials.token)
    end

    # Anything yielded from this block is passed to on_update
    yield "Logged in!"

    # Return value of block is passed back to on_finish
    credentials != nil
  end

  on_start do
    # This block runs on the UI thread after the operation has been queued.
    SVProgressHUD.showWithStatus("Logging In...")
  end

  on_update do |status|
    # This block runs on the UI thread with anything the task yields
    puts status
  end

  on_finish do |result, exception|
    # This block runs on the UI thread after the task block has finished.
    SVProgressHUD.dismiss

    if exception == nil
      if result
        alert("Logged in successfully!")
      else
        alert("Invalid username/password!")
      end
    else
      alert(exception)
    end
  end
end

Background

Many iOS/OS X apps have fairly simple domain logic that is obscured by several programming 'taxes':

• UI management
• asynchronous network requests
• I/O-heavy operations, such as storing large datasets to disk

These are necessary to ensure a good user experience, but they splinter your domain logic (that is, what your application does) through your view controller. Gross.

Elevate is a mini task queue for your app, much like Resque or Sidekiq. Rather than defining part of an operation to run on the UI thread, and a CPU-intensive portion on a background thread, Elevate is designed so you run the entire operation in the background, and receive notifications at various times. This has a nice side effect of consolidating all the interaction for a particular task to one place. The UI code is cleanly isolated from the non-UI code. When your tasks become complex, you can elect to extract them out to a service object.

In a sense, Elevate is almost a control-flow library: it bends the rules of app development a bit to ensure that the unique value your application provides is as clear as possible.

Tutorial

If you're new to Elevate, please start with the tutorial.

Installation

Update your Gemfile:

gem "elevate", "~> 0.6.0"

Bundle:

$ bundle install

Usage

Include the module in your view controller:

class ArtistsSearchViewController < UIViewController
  include Elevate

Launch an async task with the async method:

@track_task = async artist: searchBar.text do
  task do
    response = Elevate::HTTP.get("http://example.com/artists", query: { artist: @artist })

    artist = Artist.from_hash(response)
    ArtistDB.update(artist)

    response["name"]
  end

  on_start do
    SVProgressHUD.showWithStatus("Adding...")
  end

  on_finish do |result, exception|
    SVProgressHUD.dismiss
  end
end

If you might need to cancel the task later, call cancel on the object returned by async:

@track_task.cancel

Timeouts

Elevate 0.6.0 includes support for timeouts. Timeouts are declared using the timeout method within the async block. They start when an operation is queued, and automatically abort the task when the duration passes. If the task takes longer than the specified duration, the on_timeout callback is run.

Example:

async do
  timeout 0.1

  task do
    Elevate::HTTP.get("http://example.com/")
  end

  on_timeout do
    puts 'timed out'
  end

  on_finish do |result, exception|
    puts 'completed!'
  end
end

Caveats

• Must use Elevate's HTTP client instead of other iOS networking libs

Inspiration

• Hexagonal Architecture
• Android SDK's AsyncTask
• Go (asynchronous IO done correctly)

License

MIT License