The DialogueRunner class is used to execute the dialogue at runtime. If you think of a YarnProject as a dialogue program consisting of multiple Nodes as “functions”, then a DialogueRunner is the virtual machine that can run a single “function” within that “program”.

A single DialogueRunner may only execute one dialogue Node at a time. It is an error to try to run another Node before the first one concludes. However, it is possible to create multiple DialogueRunners for the same YarnProject, and then they would be able to execute multiple dialogues simultaneously (for example, in a crowded room there could be multiple dialogues occurring at once with different groups of people).

The job of a DialogueRunner is to fetch the dialogue lines in the correct order and at the appropriate pace, to execute the logic in dialogue scripts, and to branch according to user input in DialogueChoices. The output of a DialogueRunner, therefore, is a stream of dialogue statements that need to be presented to the player. Such presentation, is handled by the DialogueViews.


The constructor takes two required parameters:

yarnProject YarnProject

The YarnProject which the dialogue runner will be executing.

dialogueViews List<DialogueView>

The list of DialogueViews that will be presenting the dialogue within the game. Each of these DialogueViews can only be assigned to a single DialogueRunner at a time.


project YarnProject

The YarnProject within which the dialogue runner is running.


startDialogue(String nodeName)

Executes the node with the given name, and returns a future that completes only when the dialogue finishes running (which may be a while). A single DialogueRunner can only run one node at a time.

sendSignal(dynamic signal)

Delivers the given signal to all dialogue views, in the form of a DialogueView method onLineSignal(line, signal). This can be used, for example, as a means of communication between the dialogue views.

The signal object here is completely arbitrary, and it is up to the implementations to decide which signals to send and to receive. Implementations should ignore any signals they do not understand.


Requests (via onLineStop()) that the presentation of the current line be finished as quickly as possible. The dialogue will then proceed normally to the next line.

Execution model

The DialogueRunner uses futures as a main mechanism for controlling the timing of the dialogue progression. For each event, the dialogue runner will invoke the corresponding callback on all its DialogueViews, and each of those callbacks may return a future. The dialogue runner then awaits on all of these futures (in parallel), before proceeding to the next event.

For a simple .yarn script like this

title: main
-> Hi
-> Go away
   <<jump Away>>

title: Away

the sequence of emitted events will be as follows (assuming the second option is selected):

  • onDialogueStart()

  • onNodeStart(Node("main"))

  • onLineStart(Line("Hello"))

  • onLineFinish(Line("Hello"))

  • onChoiceStart(Choice(["Hi", "Go away"]))

  • onChoiceFinish(Option("Go away"))

  • onNodeFinish(Node("main"))

  • onNodeStart(Node("Away"))

  • onCommand(Command("OhNo"))

  • onNodeFinish(Node("Away"))

  • onDialogueFinish()


Keep in mind that if a DialogueError is thrown while running the dialogue, then the dialogue will terminate immediately and none of the *Finish callbacks will run.