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

    All Methods Instance Methods Abstract Methods
    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 Detail

    - #### 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`