VibeCoding/.agents/skills/camerax/references/immutability.md

Many Android APIs are designed with immutability in mind to prevent race conditions in async environments. However, this often trips up developers used to mutable builder patterns.

Common immutable classes

The following classes use fluent APIs that return a new instance. You must reassign the variable.

Class	Methods that return a new instance	Result if not reassigned
PendingRecording	withAudioEnabled, asPersistentRecording	Audio isn't recorded.
ImageCapture.Builder	setTargetRotation, setTargetResolution	The output has the wrong orientation.
Recorder.Builder	setQualitySelector, setExecutor	The recording uses the default quality.
Viewport.Builder	setScaleType, setLayoutDirection	The viewfinder is stretched.

Use standard patterns

CameraX video recording

To set up video recording, use the following code:

// WRONG
run {
  val pending = recorder.prepareRecording(context, opts)
  pending.withAudioEnabled() // This returns a new instance which is ignored
  val active = pending.start(exec, listener)
}

// CORRECT
run {
  val pending = recorder.prepareRecording(context, opts)
      .withAudioEnabled() // Chaining works
  val active = pending.start(exec, listener)
}

// ALSO CORRECT
run {
  var pending = recorder.prepareRecording(context, opts)
  pending = pending.withAudioEnabled() // Reassignment
  val active = pending.start(exec, listener)
}

Viewport construction

To set up the viewport, use the following code:

val viewport = ViewPort.Builder(Rational(width, height), displayRotation)
    .setScaleType(ViewPort.FILL_CENTER)
    .build()