Package org.apache.tapestry5.services

# Interface Heartbeat

All Known Implementing Classes:
  `HeartbeatImpl`

public interface Heartbeat
Allows for deferred execution of logic, useful when trying to get multiple components to coordinate behavior. A component may add a command to be executed "at the end of the heartbeat". The classic example of this is a Label and the field it labels; since we don't know which order the two will render, we can't tell if the field's id is correct until after both have rendered. The Heartbeat is injected into components via the `Environmental` annotation.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `begin()`
  Begins a new Heartbeat.
  `void`
  `defer(Runnable command)`
  Adds a new command to the current Heartbeat.
  `void`
  `end()`
  Executes all commands since the most recent `begin()`.

- ## Method Details

  - ### begin

    void begin()
    Begins a new Heartbeat. Heartbeats nest. Every call to begin() should be matched by a call to `end()`.

  - ### end

    void end()
    Executes all commands since the most recent `begin()`.

  - ### defer

    void defer(Runnable command)
    Adds a new command to the current Heartbeat. The command will be executed by `end()`.
    Parameters:
      `command` - command to be executed at the end of the heartbeat
    See Also:
      - `HeartbeatDeferred`