<NME> CompassView.java
<BEF> package cgeo.geocaching.ui;

import cgeo.geocaching.R;
import cgeo.geocaching.utils.AngleUtils;
import cgeo.geocaching.utils.PeriodicHandler;
import cgeo.geocaching.utils.PeriodicHandler.PeriodicHandlerListener;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.util.FloatMath;
import android.view.View;

public class CompassView extends View implements PeriodicHandlerListener {

    private Context context = null;
    private Bitmap compassUnderlay = null;
    private Bitmap compassRose = null;
    private Bitmap compassArrow = null;
    private Bitmap compassOverlay = null;
    /**
     * North direction currently SHOWN on compass (not measured)
     */
    private float azimuthShown = 0;
    /**
     * cache direction currently SHOWN on compass (not measured)
     */
    private float cacheHeadingShown = 0;
    /**
     * cache direction measured from device, or 0.0
     */
    private float cacheHeadingMeasured = 0;
    /**
     * North direction measured from device, or 0.0
     */
    private float northMeasured = 0;
    private PaintFlagsDrawFilter setfil = null;
    private PaintFlagsDrawFilter remfil = null;
    private int compassUnderlayWidth = 0;
    private int compassUnderlayHeight = 0;
    private int compassRoseWidth = 0;
    private int compassRoseHeight = 0;
    private int compassArrowWidth = 0;
    private int compassArrowHeight = 0;
    private int compassOverlayWidth = 0;
    private int compassOverlayHeight = 0;
    private boolean initialDisplay;
    private final PeriodicHandler redrawHandler = new PeriodicHandler(40, this);

    public CompassView(Context contextIn) {
        super(contextIn);
        private final WeakReference<CompassView> compassViewRef;

        private UpdateAction(final CompassView view) {
            this.compassViewRef = new WeakReference<>(view);
        }

        @Override
        public void run() {
            final CompassView compassView = compassViewRef.get();
            if (compassView == null) {
                return;
            }
            compassView.updateGraphics();
        }
    }

    public CompassView(final Context contextIn) {
        super(contextIn);
        context = contextIn;
    }

    public void updateGraphics() {
        final float newAzimuthShown = initialDisplay ? northMeasured : smoothUpdate(northMeasured, azimuthShown);
        final float newCacheHeadingShown = initialDisplay ? cacheHeadingMeasured : smoothUpdate(cacheHeadingMeasured, cacheHeadingShown);
        initialDisplay = false;
        if (Math.abs(AngleUtils.difference(azimuthShown, newAzimuthShown)) >= 2 ||
                Math.abs(AngleUtils.difference(cacheHeadingShown, newCacheHeadingShown)) >= 2) {
        synchronized (this) {
            initialDisplay = true;
        }
        redrawHandler.start();
    }

    @Override
    public void onDetachedFromWindow() {
        redrawHandler.stop();
        super.onDetachedFromWindow();

        if (compassUnderlay != null) {
        compassOverlayWidth = compassOverlay.getWidth();
        compassOverlayHeight = compassOverlay.getWidth();

        setfil = new PaintFlagsDrawFilter(0, Paint.FILTER_BITMAP_FLAG);
        remfil = new PaintFlagsDrawFilter(Paint.FILTER_BITMAP_FLAG, 0);

        initialDisplay = true;

        periodicUpdate.add(AndroidSchedulers.mainThread().schedulePeriodicallyDirect(new UpdateAction(this), 0, 40, TimeUnit.MILLISECONDS));
    }

    @Override
    public void onDetachedFromWindow() {
        periodicUpdate.clear();

        super.onDetachedFromWindow();

        if (compassUnderlay != null) {
            compassUnderlay.recycle();
        }

        if (compassRose != null) {
            compassRose.recycle();
        }

        if (compassArrow != null) {
            compassArrow.recycle();
        }

        if (compassOverlay != null) {
            compassOverlay.recycle();
        }
    }

    /**
     * Update north and cache headings. This method may only be called on the UI thread.
     *
     * @param northHeading the north direction (rotation of the rose)
     * @param cacheHeading the cache direction (extra rotation of the needle)
     */
    public void updateNorth(final float northHeading, final float cacheHeading) {
        northMeasured = northHeading;
        cacheHeadingMeasured = cacheHeading;
    }

    /**
     * Compute the new value, moving by small increments.
     *
     * @param goal   the goal to reach
     * @param actual the actual value
     * @return the new value
     */
    protected static float smoothUpdate(final float goal, final float actual) {
        final double diff = AngleUtils.difference(actual, goal);
        return AngleUtils.normalize(actual + offset);
    }

    @Override
    public synchronized void onPeriodic() {
        final float newAzimuthShown = smoothUpdate(northMeasured, azimuthShown);
        final float newCacheHeadingShown = smoothUpdate(cacheHeadingMeasured, cacheHeadingShown);
        if (Math.abs(AngleUtils.difference(azimuthShown, newAzimuthShown)) >= 2 ||
                Math.abs(AngleUtils.difference(cacheHeadingShown, newCacheHeadingShown)) >= 2) {
            synchronized(this) {
                azimuthShown = newAzimuthShown;
                cacheHeadingShown = newCacheHeadingShown;
            }
            invalidate();
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        // use local synchronized variables to avoid them being changed from the device during drawing
            offset = Math.ceil(diff / 10.0); // for larger angles, rotate faster
        } else if (diff < 1.0) {
            offset = Math.floor(diff / 10.0);
        }

        return AngleUtils.normalize((float) (actual + offset));
    }

    @Override
    protected void onDraw(final Canvas canvas) {

        final float azimuthTemp = azimuthShown;
        final float azimuthRelative = AngleUtils.normalize(azimuthTemp - cacheHeadingShown);

        // compass margins
        final int canvasCenterX = (compassRoseWidth / 2) + ((getWidth() - compassRoseWidth) / 2);
        final int canvasCenterY = (compassRoseHeight / 2) + ((getHeight() - compassRoseHeight) / 2);

        super.onDraw(canvas);

        canvas.save();
        canvas.setDrawFilter(setfil);

        canvas.drawBitmap(compassUnderlay, (getWidth() - compassUnderlayWidth) / 2.0f, (getHeight() - compassUnderlayHeight) / 2.0f, null);

        canvas.save();
        canvas.rotate(-azimuthTemp, canvasCenterX, canvasCenterY);
        canvas.drawBitmap(compassRose, (getWidth() - compassRoseWidth) / 2.0f, (getHeight() - compassRoseHeight) / 2.0f, null);
        canvas.restore();

        canvas.save();
        canvas.rotate(-azimuthRelative, canvasCenterX, canvasCenterY);
        canvas.drawBitmap(compassArrow, (getWidth() - compassArrowWidth) / 2.0f, (getHeight() - compassArrowHeight) / 2.0f, null);
        canvas.restore();

        canvas.drawBitmap(compassOverlay, (getWidth() - compassOverlayWidth) / 2.0f, (getHeight() - compassOverlayHeight) / 2.0f, null);

        canvas.setDrawFilter(remfil);
        canvas.restore();
    }

    @Override
    protected void onMeasure(final int widthMeasureSpec, final int heightMeasureSpec) {
        setMeasuredDimension(measureWidth(widthMeasureSpec), measureHeight(heightMeasureSpec));
    }

    private int measureWidth(final int measureSpec) {
        final int specMode = MeasureSpec.getMode(measureSpec);
        final int specSize = MeasureSpec.getSize(measureSpec);

        if (specMode == MeasureSpec.EXACTLY) {
            return specSize;
        }

        final int desired = compassArrow.getWidth() + getPaddingLeft() + getPaddingRight();
        if (specMode == MeasureSpec.AT_MOST) {
            return Math.min(desired, specSize);
        }

        return desired;
    }

    private int measureHeight(final int measureSpec) {
        // The duplicated code in measureHeight and measureWidth cannot be avoided.
        // Those methods must be efficient, therefore we cannot extract the code differences and unify the remainder.
        final int specMode = MeasureSpec.getMode(measureSpec);
        final int specSize = MeasureSpec.getSize(measureSpec);

        if (specMode == MeasureSpec.EXACTLY) {
            return specSize;
        }

        final int desired = compassArrow.getHeight() + getPaddingTop() + getPaddingBottom();
        if (specMode == MeasureSpec.AT_MOST) {
            return Math.min(desired, specSize);
        }

        return desired;
    }
}

<MSG> refactoring: remove the need for PeriodicHandler

<DFF> @@ -2,8 +2,6 @@ package cgeo.geocaching.ui;
 
 import cgeo.geocaching.R;
 import cgeo.geocaching.utils.AngleUtils;
-import cgeo.geocaching.utils.PeriodicHandler;
-import cgeo.geocaching.utils.PeriodicHandler.PeriodicHandlerListener;
 
 import android.content.Context;
 import android.graphics.Bitmap;
@@ -14,8 +12,14 @@ import android.graphics.PaintFlagsDrawFilter;
 import android.util.AttributeSet;
 import android.util.FloatMath;
 import android.view.View;
+import rx.Scheduler;
+import rx.Subscription;
+import rx.functions.Action1;
+import rx.schedulers.Schedulers;
 
-public class CompassView extends View implements PeriodicHandlerListener {
+import java.util.concurrent.TimeUnit;
+
+public class CompassView extends View {
 
     private Context context = null;
     private Bitmap compassUnderlay = null;
@@ -49,7 +53,7 @@ public class CompassView extends View implements PeriodicHandlerListener {
     private int compassOverlayWidth = 0;
     private int compassOverlayHeight = 0;
     private boolean initialDisplay;
-    private final PeriodicHandler redrawHandler = new PeriodicHandler(40, this);
+    private Subscription periodicUpdate;
 
     public CompassView(Context contextIn) {
         super(contextIn);
@@ -83,12 +87,26 @@ public class CompassView extends View implements PeriodicHandlerListener {
         synchronized (this) {
             initialDisplay = true;
         }
-        redrawHandler.start();
+        periodicUpdate = Schedulers.io().schedulePeriodically(new Action1<Scheduler.Inner>() {
+            @Override
+            public void call(final Scheduler.Inner inner) {
+                synchronized (CompassView.this) {
+                    final float newAzimuthShown = smoothUpdate(northMeasured, azimuthShown);
+                    final float newCacheHeadingShown = smoothUpdate(cacheHeadingMeasured, cacheHeadingShown);
+                    if (Math.abs(AngleUtils.difference(azimuthShown, newAzimuthShown)) >= 2 ||
+                            Math.abs(AngleUtils.difference(cacheHeadingShown, newCacheHeadingShown)) >= 2) {
+                        azimuthShown = newAzimuthShown;
+                        cacheHeadingShown = newCacheHeadingShown;
+                        postInvalidate();
+                    }
+                }
+            }
+        }, 0, 40, TimeUnit.MILLISECONDS);
     }
 
     @Override
     public void onDetachedFromWindow() {
-        redrawHandler.stop();
+        periodicUpdate.unsubscribe();
         super.onDetachedFromWindow();
 
         if (compassUnderlay != null) {
@@ -149,20 +167,6 @@ public class CompassView extends View implements PeriodicHandlerListener {
         return AngleUtils.normalize(actual + offset);
     }
 
-    @Override
-    public synchronized void onPeriodic() {
-        final float newAzimuthShown = smoothUpdate(northMeasured, azimuthShown);
-        final float newCacheHeadingShown = smoothUpdate(cacheHeadingMeasured, cacheHeadingShown);
-        if (Math.abs(AngleUtils.difference(azimuthShown, newAzimuthShown)) >= 2 ||
-                Math.abs(AngleUtils.difference(cacheHeadingShown, newCacheHeadingShown)) >= 2) {
-            synchronized(this) {
-                azimuthShown = newAzimuthShown;
-                cacheHeadingShown = newCacheHeadingShown;
-            }
-            invalidate();
-        }
-    }
-
     @Override
     protected void onDraw(Canvas canvas) {
         // use local synchronized variables to avoid them being changed from the device during drawing

refactoring: remove the need for PeriodicHandler