ImageTrigger.kt

/**
 * Execute a new capture request within the active session
 */

private fun triggerImageCapture() {
    try {
        val captureBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE)
        captureBuilder.addTarget(imageReader.getSurface())
        captureBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON)
        Log.d(TAG, "Capture request created.")
        captureSession.capture(captureBuilder.build(), captureCallback, null)
    } catch (cae: CameraAccessException) {
        Log.d(TAG, "camera capture exception")
    }
}

/**
 * Callback handling capture session events
 */

private val captureCallback = object : CameraCaptureSession.CaptureCallback() {
    override fun onCaptureProgressed(session: CameraCaptureSession,
                                     request: CaptureRequest,
                                     partialResult: CaptureResult) {
        Log.d(TAG, "Partial result")
    }

    override fun onCaptureCompleted(session: CameraCaptureSession,
                                    request: CaptureRequest,
                                    result: TotalCaptureResult) {
        session.close()
        captureSession = null
        Log.d(TAG, "CaptureSession closed")
    }
}