Session State

A measuring session is always in a "state". The session transitions between possible states either by following an API action called by the application, or via internal logic that is intended to prepare the session for performing measurements. The session state diagram appears in the figure below.

Session States

The table below provides a description of each session state:

State Name	State Definition
INIT	The session is in its initial state, performing initialization actions. Please wait until you receive the message indicating that the session is in the ACTIVE state before starting to measure vital signs or before calling any session APIs.
ACTIVE	The session is now ready to be started. The application can display the camera preview, if using face measurements. Refer to the Creating a Preview page for detailed instructions.
MEASURING	The session is processing the data and calculating vital signs. For information on the handling of instantaneous vital signs, please refer to the Vital Signs page.
STOPPING	The session has been stopped, and the measurement results are being calculated. For information on the handling the final results, please see the Vital Signs page.
TERMINATED	The session has been gracefully terminated, and a new session can now be initiated.

Session State Transitions

The table below describes the actions that cause a transition between the states:

State	Next State	Trigger
INIT	ACTIVE	Once all initialization actions are completed, the session transitions to the ACTIVE state.
ACTIVE	MEASURING	Calling the start() method causes the session to transition to the MEASURING state.
MEASURING	STOPPING	The session will transition to the STOPPING state under the following circumstances: *The measurement ends gracefully either because it reached the defined duration or due to a manual invocation of the stop() method. *The measurement was stopped due to an error. Refer to the Alerts section for more information.
STOPPING	ACTIVE	The SDK has finished performing the vital sign calculations.
READY	TERMINATED	By calling the terminate() method, the session transitions to the TERMINATED state.

Note

The STOPPING state is a 'transition state' that end automatically after a short period. Do not call any session methods while the session is in transition.

Receiving Session State Updates

The application can receive session state updates by using OnStateChange callback:

TypeScript

import { 
    SessionState, 
} from '@biosensesignal/web-sdk';

const onStateChange = useCallback((state: SessionState) => {
    // Receive session state updates
}, []);

Handling State Transitions

The code below is a simple example for handling session transitions updates by using OnStateChange callback:

TypeScript

import { 
    SessionState, 
} from '@biosensesignal/web-sdk';

const onStateChange = useCallback((state: SessionState) => {
    switch (state) {
        case SessionState.INIT:
            console.log("Session is initializing and NOT ready");
            break;
        case SessionState.ACTIVE:
            console.log("Session is ready to start measuring");
            break;
        case SessionState.MEASURING:
            console.log("Session is measuring vital signs");
            break;
        case SessionState.STOPPING:
            console.log("Session is stopping the measuring of vital signs");
            break;
        case SessionState.TERMINATED:
            console.log("Session is terminated");
            break;
    }
}, []);