# Stationary Development


## When to Use

An application can call the **Stationary** module to obtain the device status, for example, whether the device is absolutely or relatively still.

For details about the APIs, see [Stationary](../reference/apis/js-apis-stationary.md).

## Device Status Type Parameters

| Name| Description|
| -------- | -------- |
| still | Absolutely still.|
| relativeStill | Relatively still.|

## Parameters for Subscribing to Device Status events

| Name                            | Value   | Description                                      |
| ------------------------------ | ---- | ---------------------------------------- |
| ENTER         | 1    | Event indicating entering device status.  |
| EXIT | 2   | Event indicating exiting device status.|
| ENTER_EXIT | 3   | Event indicating entering and exiting device status.|

## Returned Device Status Parameters

| Name                            | Value   | Description                                      |
| ------------------------------ | ---- | ---------------------------------------- |
| ENTER         | 1    | Entering device status.  |
| EXIT | 2   | Exiting device status.|

## Available APIs

| Module         | Name                                                      | Description                                                        |
| ------------- | ------------------------------------------------------------ | ------------------------------------------------------------ |
| ohos.stationary | on(activity: ActivityType, event: ActivityEvent, reportLatencyNs: number, callback: Callback<ActivityResponse>): void | Subscribes to the device status. This API uses an asynchronous callback to return the result.|
| ohos.stationary | once(activity: ActivityType, callback: Callback<ActivityResponse>): void | Obtains the device status. This API uses an asynchronous callback to return the result.|
| ohos.stationary | off(activity: ActivityType, event: ActivityEvent, callback?: Callback<ActivityResponse>): void | Unsubscribes from the device status.                                |

## Constraints

The device must support the acceleration sensor.

## How to Develop

1. Subscribe to the event indicating entering the absolute still state, and the event is reported every 1 second.

   ```js
   import stationary from '@ohos.stationary';
   var reportLatencyNs = 1000000000;
   try {
      stationary.on('still', stationary.ActivityEvent.ENTER, reportLatencyNs, (data) => {
         console.log('data='+ JSON.stringify(data));
      })
   } catch (err) {
      console.error('errCode: ' + err.code + ' ,msg: ' + err.message);
   }
   ```

2. Obtain the event indicating entering the absolute still state.

   ```js
   import stationary from '@ohos.stationary';
   try {
      stationary.once('still', (data) => {
         console.log('data='+ JSON.stringify(data));
      })
   } catch (err) {
      console.error('errCode: ' + err.code + ' ,msg: ' + err.message);
   }
   ```

3. Unsubscribe from the event indicating entering the absolute still state.

   ```js
   import stationary from '@ohos.stationary';
   try {
      stationary.off('still', stationary.ActivityEvent.ENTER, (data) => {
         console.log('data='+ JSON.stringify(data));
      })
   } catch (err) {
      console.error('errCode: ' + err.code + ' ,msg: ' + err.message);
   }
   ```