UI features

part of kovenant-ui

Frameworks involving UIs are commonly implemented in a way that only one thread is allowed to interact with that UI. Android, Swing, AWT and JavaFX all use this strategy. For this reason Kovenant-UI offers a generic way for executing callbacks of promises on that specific UI thread.

UI callbacks

The most flexible way of interacting with the main thread is by using the extension methods. The kovenant-ui library provides successUi, failUi and alwaysUi. They operate just like their regular counterparts except their bodies are executed on the configured UI thread. Both type of callbacks can be mixed freely.

val promise = task {
    foo() //produces 'bar'

promise success {
    //no need to do this on the
    //main thread
    bar -> writeLog(bar)

promise successUi {
    //also update the interface
    bar -> updateUI(bar)

The huge advantage of this approach is that operations on the main thread are explicitly chosen.

Start on UI thread

You might want to do some preparations on the UI thread before you start your background work. This is what promiseOnUi does, it schedules a task on the UI thread and returns a Promise on which you can chain along.

promiseOnUi {
    //prepare the UI
} then {
    //do background work
} successUi {
    //post the results


Kovenant UI just requires a minimal setup: It needs to know where to dispatch the callback to. So all that is needed is configure it with a Dispatcher that operates on the desired thread, like this:

KovenantUi.uiContext {
    dispatcher = myUiDispatcher


When you configure Kovenant UI with a ProcessAwareDispatcher calls can sometimes be optimized. A ProcessAwareDispatcher knows which threads/tasks/processes it owns and therefor scheduling of tasks can sometimes be avoided. All the ui callbacks have a parameter alwaysSchedule, which is false by default, which tells whether a specific callback always gets scheduled/queued or that it may be optimized.