# Sensor Development


## When to Use

- Data provided by the compass sensor denotes the current orientation of the user device, which helps your application accurately navigate for the user.

- Data provided by the proximity sensor denotes the distance between the device and a visible object, which enables the device to automatically turn on or off its screen accordingly to prevent accidental touch on the screen.

- Data provided by the barometer sensor helps your application accurately determine the altitude of the device.

- Data provided by the ambient light sensor helps your device automatically adjust its backlight.

- Data provided by the Hall effect sensor implements the smart cover mode of your device.

- Data provided by the heart rate sensor helps your application track the heart health of a user.

- Data provided by the pedometer sensor helps your application obtain the number of steps a user has walked.

- Data provided by the wear detection sensor helps your application detect whether a user is wearing a wearable device.


## Available APIs

| Module| API| Description|
| -------- | -------- | -------- |
| ohos.sensor | sensor.on(sensorType, callback:AsyncCallback<Response>): void | Subscribes to data changes of a type of sensor.|
| ohos.sensor | sensor.once(sensorType, callback:AsyncCallback<Response>): void | Subscribes to only one data change of a type of sensor.|
| ohos.sensor | sensor.off(sensorType, callback:AsyncCallback<void>): void | Unsubscribes from sensor data changes.|


## How to Develop

1. To obtain data from a type of sensor, configure the requested permissions in the **config.json** file.  
  
   ```
   "reqPermissions":[
     {
        "name":"ohos.permission.ACCELEROMETER",
        "reason":"", 
        "usedScene":{
         "ability": ["sensor.index.MainAbility",".MainAbility"],
         "when":"inuse"
       }
     },
     {
        "name":"ohos.permission.GYROSCOPE",
        "reason":"", 
        "usedScene":{
         "ability": ["sensor.index.MainAbility",".MainAbility"],
         "when":"inuse"
       }
     },
     {
        "name":"ohos.permission.ACTIVITY_MOTION",
        "reason":"ACTIVITY_MOTION_TEST", 
        "usedScene":{
         "ability": ["sensor.index.MainAbility",".MainAbility"],
         "when":"inuse"
       }
     },
     {
        "name":"ohos.permission.READ_HEALTH_DATA",
        "reason":"HEALTH_DATA_TEST", 
        "usedScene":{
         "ability": ["sensor.index.MainAbility",".MainAbility"],
         "when":"inuse"
       }
     },
   ]
   ```
   
2. Subscribe to data changes of a type of sensor.
  
   ```
   import sensor from "@ohos.sensor"
   sensor.on(sensor.sensorType.SENSOR_TYPE_ACCELEROMETER,function(data){
          console.info("Subscription succeeded. data = "+ data); // The call is successful, and the obtained sensor data is printed.
     }
   );
   ```
   
   The following figure shows the successful call result when **SensorType** is **SENSOR_TYPE_ID_ACCELEROMETER**.
   
   ![en-us_image_0000001241693881](figures/en-us_image_0000001241693881.png)

3. Unsubscribe from sensor data changes.
  
   ```
   import sensor from "@ohos.sensor"
   sensor.off(sensor.sensorType.SENSOR_TYPE_ACCELEROMETER,function() {
       console.info("Succeeded in unsubscribing from acceleration sensor data."); // The unsubscription is successful, and the result is printed.
     }
   );
   ```
   
   The following figure shows the successful call result when **SensorType** is **SENSOR_TYPE_ID_ACCELEROMETER**.
   
   ![en-us_image_0000001196654004](figures/en-us_image_0000001196654004.png)

4. Subscribe to only one data change of a type of sensor.
  
   ```
   import sensor from "@ohos.sensor"
   sensor.once(sensor.sensorType.SENSOR_TYPE_ACCELEROMETER,function(data) {
           console.info("Data obtained successfully. data=" + data); // The call is successful, and the obtained sensor data is printed.
     }
   );
   ```
   
   The following figure shows the successful call result when **SensorType** is **SENSOR_TYPE_ID_ACCELEROMETER**.
   
   ![en-us_image_0000001241733907](figures/en-us_image_0000001241733907.png)

   If the API fails to be called, you are advised to use the **try/catch** statement to capture error information that may occur in the code. Example:

    ```
    try {
      sensor.once(sensor.sensorType.SENSOR_TYPE_ACCELEROMETER,function(data) {
          console.info("Data obtained successfully. data=" + data); // The call is successful, and the obtained sensor data is printed.
      });
    } catch (error) {
      console.error(error);
    }
    ```