Add a check to verify if the sensor exist

ExampleBehaviour/SensorBehaviour.cs

@@ -30,10 +30,12 @@ void Update ()
 	{
 #if UNITY_ANDROID
 		if (plugin != null) {
-			float[] sensorValue = plugin.Call<float[]>("getSensorValues", "accelerometer");
-			if (sensorValue != null) {
-				Debug.Log("sensorValue:" + string.Join(",", new List<float>(sensorValue).ConvertAll(i => i.ToString()).ToArray()));
-			}
+            if (plugin.Call<bool>("hasSensor", "accelerometer") == true) {
+			    float[] sensorValue = plugin.Call<float[]>("getSensorValues", "accelerometer");
+			    if (sensorValue != null) {
+				    Debug.Log("sensorValue:" + string.Join(",", new List<float>(sensorValue).ConvertAll(i => i.ToString()).ToArray()));
+			    }
+            }
 		}
 #endif
 	}

README.md

@@ -86,6 +86,15 @@ This makes enable more frequently method calling than game FPS.
         }
 ```
 
+Verify if a sensor exist
+```c#
+#if UNITY_ANDROID
+       if (plugin.Call<bool>("hasSensor", "accelerometer") == true) {
+                Debug.log("accelerometer exist");
+       }
+#endif
+```
+
 Available Sensors
 ----
 * accelerometer

library/src/main/java/jp/kshoji/unity/sensor/UnitySensorPlugin.java

@@ -47,6 +47,32 @@ public static UnitySensorPlugin getInstance() {
         return result;
     }
 
+    /**
+     * Get if the sensor is valid
+     * Called by Unity
+     *
+     * @param sensorKind sensor kind @see {@link Sensors}
+     * @return true if the sensor exist
+     */
+
+    public boolean hasSensor(String sensorKind) {
+
+        Sensors specifiedSensor;
+        try {
+            specifiedSensor = Sensors.valueOf(sensorKind);
+        } catch (IllegalArgumentException e) {
+            // valueOf failed
+            Log.e(getClass().getName(), "Bad sensor type: " + sensorKind + ", available types: " + Arrays.toString(Sensors.values()));
+            return false;
+        }
+
+       if( sensorManager.getDefaultSensor( specifiedSensor.getSensorType() ) == null) {
+              return false;
+       }
+
+        return true;
+    }
+
     /**
      * Terminates instance
      * Must be called on App's last use.
@@ -104,6 +130,22 @@ public void startSensorListening(String sensorKind) {
         addSensorEventListener(sensorKind, null, null);
     }
 
+    /**
+     * Stop to listen sensor
+     * Called by Unity
+     *
+     * @param sensorKind sensor kind @see {@link Sensors}
+     * @return true if the listener is destroyed
+     */
+    public boolean stopSensorListening(String sensorKind) {
+        String sensorKindConverted = convertSensorKind(sensorKind);
+        if(eventListeners.containsKey(sensorKindConverted)) {
+            eventListeners.remove(sensorKindConverted);
+            return true;
+        }
+        return false;
+    }
+
     /**
      * Add sensor listener with callback
      * Called by Unity