Adjust for unit mismatch: event.timestamp is in nanoseconds, not milliseconds

app/src/main/java/cse340/sensing/SensorActivity.java

@@ -11,6 +11,7 @@ import android.hardware.SensorEvent;
 import android.hardware.SensorEventListener;
 import android.hardware.SensorManager;
 import android.os.Bundle;
+import android.os.SystemClock;
 import android.view.LayoutInflater;
 import android.view.Menu;
 import android.widget.TableLayout;
@@ -38,6 +39,9 @@ public class SensorActivity extends AbstractMainActivity implements SensorEventL
      */
     private static final int DELAY = SensorManager.SENSOR_DELAY_UI;
 
+    /** Minimum update time for _some_ of the sensors below, in nanoseconds. */
+    private static final long MIN_UPDATE_DELAY = 200 * 1000 * 1000;
+
     /**
      * Constants for creating the IDs for the table rows, and children in the row
      */
@@ -52,6 +56,9 @@ public class SensorActivity extends AbstractMainActivity implements SensorEventL
 
     /**
      * The last time the screen was updated - this is so we can actually see the values
+     * This is in nanoseconds since the time the device was booted.
+     *
+     * @see SystemClock#elapsedRealtimeNanos()
      */
     private long mLastUpdate;
 
@@ -82,7 +89,7 @@ public class SensorActivity extends AbstractMainActivity implements SensorEventL
         }
 
         // Start the clock
-        mLastUpdate = System.currentTimeMillis();
+        mLastUpdate = SystemClock.elapsedRealtimeNanos();
     }
 
     /**
@@ -280,9 +287,13 @@ public class SensorActivity extends AbstractMainActivity implements SensorEventL
         double accelerationSquareRoot = Math.sqrt(x * x + y * y + z * z);
 
         String output = "";
-        if (actualTime - mLastUpdate >= 200) {
+        if (actualTime - mLastUpdate >= MIN_UPDATE_DELAY) {
             if (accelerationSquareRoot >= 1) {
                 mLastUpdate = actualTime;
+
+                // Note: We _really_ should be using strings.xml here. This makes it possible to
+                //       translate them!
+                // OPTIONAL TODO: Move these to strings.xml!
                 output = String.format(Locale.ENGLISH, "Move: %.4f",
                         accelerationSquareRoot);
             } else {
@@ -306,11 +317,9 @@ public class SensorActivity extends AbstractMainActivity implements SensorEventL
         long actualTime = event.timestamp;
         String output = "";
 
-        if (actualTime - mLastUpdate >= 200) {
+        if (actualTime - mLastUpdate >= MIN_UPDATE_DELAY) {
             mLastUpdate = actualTime;
 
-            float[] values = event.values;
-
             // Axis of the rotation sample, not normalized.
             float axisX = event.values[0];
             float axisY = event.values[1];