Shake device to clear pattern protection

app/src/main/java/com/hippo/hardware/ShakeDetector.java

@@ -0,0 +1,73 @@
+package com.hippo.hardware;
+
+import android.hardware.Sensor;
+import android.hardware.SensorEvent;
+import android.hardware.SensorEventListener;
+import android.hardware.SensorManager;
+
+// http://jasonmcreynolds.com/?p=388
+public class ShakeDetector implements SensorEventListener {
+
+    /*
+     * The gForce that is necessary to register as shake.
+     * Must be greater than 1G (one earth gravity unit).
+     * You can install "G-Force", by Blake La Pierre
+     * from the Google Play Store and run it to see how
+     *  many G's it takes to register a shake
+     */
+    private static final float SHAKE_THRESHOLD_GRAVITY = 2.7F;
+    private static final int SHAKE_SLOP_TIME_MS = 500;
+    private static final int SHAKE_COUNT_RESET_TIME_MS = 3000;
+
+    private OnShakeListener mListener;
+    private long mShakeTimestamp;
+    private int mShakeCount;
+
+    public void setOnShakeListener(OnShakeListener listener) {
+        mListener = listener;
+    }
+
+    public interface OnShakeListener {
+        void onShake(int count);
+    }
+
+    @Override
+    public void onAccuracyChanged(Sensor sensor, int accuracy) {
+        // ignore
+    }
+
+    @Override
+    public void onSensorChanged(SensorEvent event) {
+
+        if (mListener != null) {
+            float x = event.values[0];
+            float y = event.values[1];
+            float z = event.values[2];
+
+            float gX = x / SensorManager.GRAVITY_EARTH;
+            float gY = y / SensorManager.GRAVITY_EARTH;
+            float gZ = z / SensorManager.GRAVITY_EARTH;
+
+            // gForce will be close to 1 when there is no movement.
+            float gForce = (float) Math.sqrt(gX * gX + gY * gY + gZ * gZ);
+
+            if (gForce > SHAKE_THRESHOLD_GRAVITY) {
+                final long now = System.currentTimeMillis();
+                // ignore shake events too close to each other (500ms)
+                if (mShakeTimestamp + SHAKE_SLOP_TIME_MS > now) {
+                    return;
+                }
+
+                // reset the shake count after 3 seconds of no shakes
+                if (mShakeTimestamp + SHAKE_COUNT_RESET_TIME_MS < now) {
+                    mShakeCount = 0;
+                }
+
+                mShakeTimestamp = now;
+                mShakeCount++;
+
+                mListener.onShake(mShakeCount);
+            }
+        }
+    }
+}