Add logger for debugging (#25)

* Add logger for debugging

* Update CameraLogger.java

* Fix #27

* More log messages

README.md

@@ -305,7 +305,7 @@ Most camera parameters can be controlled through XML attributes or linked method
 |[`cameraFlash`](#cameraflash)|`setFlash()`|`off` `on` `auto` `torch`|`off`|
 |[`cameraGrid`](#cameragrid)|`setGrid()`|`off` `draw3x3` `draw4x4` `drawPhi`|`off`|
 |[`cameraCropOutput`](#cameracropoutput)|`setCropOutput()`|`true` `false`|`false`|
-|[`cameraJpegQuality`](#camerajpegquality)|`setJpegQuality()`|`0 <= n <= 100`|`100`|
+|[`cameraJpegQuality`](#camerajpegquality)|`setJpegQuality()`|`0 < n <= 100`|`100`|
 |[`cameraVideoQuality`](#cameravideoquality)|`setVideoQuality()`|`lowest` `highest` `maxQvga` `max480p` `max720p` `max1080p` `max2160p`|`max480p`|
 |[`cameraWhiteBalance`](#camerawhitebalance)|`setWhiteBalance()`|`auto` `incandescent` `fluorescent` `daylight` `cloudy`|`auto`|
 |[`cameraHdr`](#camerahdr)|`setHdr()`|`off` `on`|`off`|
@@ -427,7 +427,7 @@ Other APIs not mentioned above are provided, and are well documented and comment
 |`getSnapshotSize()`|Returns `getPreviewSize()`, since a snapshot is a preview frame.|
 |`getPictureSize()`|Returns the size of the output picture. The aspect ratio is consistent with `getPreviewSize()`.|
 
-Take also a look at public methods in `CameraUtils`, `CameraOptions`, `ExtraProperties`.
+Take also a look at public methods in `CameraUtils`, `CameraOptions`, `ExtraProperties`, `CameraLogger`.
 
 ## Permissions behavior
 
@@ -464,6 +464,7 @@ This is what was done since the library was forked. I have kept the original str
 
 - *a huge number of serious bugs fixed*
 - *decent orientation support for both pictures and videos*
+- *less dependencies*
 - *EXIF support*
 - *real tap-to-focus support*
 - *pinch-to-zoom support*
@@ -477,30 +478,23 @@ This is what was done since the library was forked. I have kept the original str
 - *smart measuring and sizing behavior, replacing bugged `adjustViewBounds`*
 - *measure `CameraView` as center crop or center inside*
 - *add multiple `CameraListener`s for events*
-- *gesture framework support*
+- *gesture framework support, map gestures to camera controls*
+- *pinch gesture support*
+- *tap & long tap gesture support*
 - *scroll gestures support*
 - *MediaActionSound support*
 - *Hdr controls*
+- *zoom and exposure correction controls*
+- *Tests!*
+- *`CameraLogger` APIs for logging and bug reports*
+- *Better threading, start() in worker thread and callbacks in UI*
 
 These are still things that need to be done, off the top of my head:
 
-- [x] fix CropOutput class presumably not working on rotated pictures
-- [x] test video and 'frame' capture behavior, I expect some bugs there
-- [x] simple APIs to draw grid lines
-- [x] check focus, not sure it exposes the right part of the image
-- [x] replace setCameraListener() with addCameraListener()
-- [x] better threading, for example ensure callbacks are called in the ui thread
-- [x] pinch to zoom support
-- [x] exposure correction APIs
-- [x] change demo app icon
-- [x] refactor package name
-- [x] new Gestures framework to map gestures to camera controls
-- [x] heavily reduced dependencies
 - [ ] `Camera2` integration
-- [x] publish to bintray
 - [ ] check onPause / onStop / onSaveInstanceState consistency
 - [ ] add a `setPreferredAspectRatio` API to choose the capture size. Preview size will adapt, and then, if let free, the CameraView will adapt as well
 - [ ] animate grid lines similar to stock camera app
 - [ ] add onRequestPermissionResults for easy permission callback
 - [ ] better error handling, maybe with a onError(e) method in the public listener, or have each public method return a boolean
-
+- [ ] decent code coverage

cameraview/src/androidTest/java/com/otaliastudios/cameraview/CameraLoggerTest.java

@@ -0,0 +1,57 @@
+package com.otaliastudios.cameraview;
+
+
+import android.support.test.filters.SmallTest;
+import android.support.test.runner.AndroidJUnit4;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import static org.junit.Assert.*;
+
+@RunWith(AndroidJUnit4.class)
+@SmallTest
+public class CameraLoggerTest {
+
+    @Test
+    public void testLoggerLevels() {
+        CameraLogger logger = CameraLogger.create("logger");
+
+        // Verbose
+        CameraLogger.setLogLevel(CameraLogger.LEVEL_VERBOSE);
+        logger.i("i");
+        assertEquals(CameraLogger.lastMessage, "i");
+        logger.w("w");
+        assertEquals(CameraLogger.lastMessage, "w");
+        logger.e("e");
+        assertEquals(CameraLogger.lastMessage, "e");
+
+        // Warning
+        CameraLogger.lastMessage = null;
+        CameraLogger.setLogLevel(CameraLogger.LEVEL_WARNING);
+        logger.i("i");
+        assertNull(CameraLogger.lastMessage);
+        logger.w("w");
+        assertEquals(CameraLogger.lastMessage, "w");
+        logger.e("e");
+        assertEquals(CameraLogger.lastMessage, "e");
+
+        // Error
+        CameraLogger.lastMessage = null;
+        CameraLogger.setLogLevel(CameraLogger.LEVEL_ERROR);
+        logger.i("i");
+        assertNull(CameraLogger.lastMessage);
+        logger.w("w");
+        assertNull(CameraLogger.lastMessage);
+        logger.e("e");
+        assertEquals(CameraLogger.lastMessage, "e");
+    }
+
+    @Test
+    public void testLoggerObjectArray() {
+        CameraLogger.setLogLevel(CameraLogger.LEVEL_VERBOSE);
+        CameraLogger logger = CameraLogger.create("logger");
+        logger.i("test", "logger", 10, null);
+        assertEquals(CameraLogger.lastMessage, "test logger 10 null");
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/Camera1.java

@@ -26,6 +26,7 @@ import java.util.List;
 class Camera1 extends CameraController {
 
     private static final String TAG = Camera1.class.getSimpleName();
+    private static final CameraLogger LOG = CameraLogger.create(TAG);
 
     private int mCameraId;
     private Camera mCamera;
@@ -68,7 +69,7 @@ class Camera1 extends CameraController {
      */
     @Override
     public void onSurfaceAvailable() {
-        Log.e(TAG, "onSurfaceAvailable, size is "+mPreview.getSurfaceSize());
+        LOG.i("onSurfaceAvailable, size is", mPreview.getSurfaceSize());
         if (shouldSetup()) setup();
     }
 
@@ -78,7 +79,7 @@ class Camera1 extends CameraController {
      */
     @Override
     public void onSurfaceChanged() {
-        Log.e(TAG, "onSurfaceChanged, size is "+mPreview.getSurfaceSize());
+        LOG.i("onSurfaceChanged, size is", mPreview.getSurfaceSize());
         if (mIsSetup) {
             // Compute a new camera preview size.
             Size newSize = computePreviewSize();
@@ -358,8 +359,8 @@ class Camera1 extends CameraController {
                 }
                 onSurfaceChanged();
             }
-            Log.e(TAG, "captureSize: "+mCaptureSize);
+            LOG.i("captureSize: "+mCaptureSize);
-            Log.e(TAG, "previewSize: "+mPreviewSize);
+            LOG.i("previewSize: "+mPreviewSize);
         }
     }
 
@@ -508,6 +509,8 @@ class Camera1 extends CameraController {
         if (mSessionType == SessionType.PICTURE) {
             // Choose the max size.
             List<Size> captureSizes = sizesFromList(params.getSupportedPictureSizes());
+            Size maxSize = Collections.max(captureSizes);
+            LOG.i("computeCaptureSize:", "computed", maxSize, "from", captureSizes);
             return Collections.max(captureSizes);
         } else {
             // Choose according to developer choice in setVideoQuality.
@@ -516,6 +519,7 @@ class Camera1 extends CameraController {
             List<Size> captureSizes = sizesFromList(params.getSupportedPictureSizes());
             CamcorderProfile profile = getCamcorderProfile(mVideoQuality);
             AspectRatio targetRatio = AspectRatio.of(profile.videoFrameWidth, profile.videoFrameHeight);
+            LOG.i("computeCaptureSize:", "videoQuality:", mVideoQuality, "targetRatio:", targetRatio);
             return matchSize(captureSizes, targetRatio, new Size(0, 0), true);
         }
     }
@@ -524,7 +528,9 @@ class Camera1 extends CameraController {
         Camera.Parameters params = mCamera.getParameters();
         List<Size> previewSizes = sizesFromList(params.getSupportedPreviewSizes());
         AspectRatio targetRatio = AspectRatio.of(mCaptureSize.getWidth(), mCaptureSize.getHeight());
-        return matchSize(previewSizes, targetRatio, mPreview.getSurfaceSize(), false);
+        Size biggerThan = mPreview.getSurfaceSize();
+        LOG.i("computePreviewSize:", "targetRatio:", targetRatio, "surface size:", biggerThan);
+        return matchSize(previewSizes, targetRatio, biggerThan, false);
     }
 
 
@@ -721,8 +727,8 @@ class Camera1 extends CameraController {
         double theta = ((double) displayToSensor) * Math.PI / 180;
         double sensorClickX = viewClickX * Math.cos(theta) - viewClickY * Math.sin(theta);
         double sensorClickY = viewClickX * Math.sin(theta) + viewClickY * Math.cos(theta);
-        // Log.e(TAG, "viewClickX:"+viewClickX+", viewClickY:"+viewClickY);
+        LOG.i("viewClickX:", viewClickX, "viewClickY:", viewClickY);
-        // Log.e(TAG, "sensorClickX:"+sensorClickX+", sensorClickY:"+sensorClickY);
+        LOG.i("sensorClickX:", sensorClickX, "sensorClickY:", sensorClickY);
 
         // Compute the rect bounds.
         Rect rect1 = computeMeteringArea(sensorClickX, sensorClickY, 150d);
@@ -743,7 +749,7 @@ class Camera1 extends CameraController {
         int bottom = (int) Math.min(centerY + delta, 1000);
         int left = (int) Math.max(centerX - delta, -1000);
         int right = (int) Math.min(centerX + delta, 1000);
-        // Log.e(TAG, "top:"+top+", left:"+left+", bottom:"+bottom+", right:"+right);
+        LOG.i("metering area:", "top:", top, "left:", left, "bottom:", bottom, "right:", right);
         return new Rect(left, top, right, bottom);
     }
 
@@ -762,6 +768,7 @@ class Camera1 extends CameraController {
         for (Camera.Size size : sizes) {
             result.add(new Size(size.width, size.height));
         }
+        LOG.i("sizesFromList:", result.toArray());
         return result;
     }
 
@@ -791,15 +798,20 @@ class Camera1 extends CameraController {
             }
         }
 
+        LOG.i("matchSize:", "found consistent:", consistent.size());
+        LOG.i("matchSize:", "found big enough and consistent:", bigEnoughAndConsistent.size());
+        Size result;
         if (biggestPossible) {
             if (bigEnoughAndConsistent.size() > 0) return Collections.max(bigEnoughAndConsistent);
             if (consistent.size() > 0) return Collections.max(consistent);
-            return Collections.max(sizes);
+            result = Collections.max(sizes);
         } else {
             if (bigEnoughAndConsistent.size() > 0) return Collections.min(bigEnoughAndConsistent);
             if (consistent.size() > 0) return Collections.max(consistent);
-            return Collections.max(sizes);
+            result = Collections.max(sizes);
         }
+        LOG.i("matchSize:", "returning result", result);
+        return result;
     }
 
 

cameraview/src/main/java/com/otaliastudios/cameraview/Camera2.java

@@ -107,7 +107,6 @@ class Camera2 extends CameraController {
         try {
             ids = mCameraManager.getCameraIdList();
         } catch (CameraAccessException e) {
-            Log.e("CameraKit", e.toString());
             return;
         }
 

cameraview/src/main/java/com/otaliastudios/cameraview/CameraView.java

@@ -44,6 +44,8 @@ import static android.view.ViewGroup.LayoutParams.MATCH_PARENT;
 public class CameraView extends FrameLayout {
 
     private final static String TAG = CameraView.class.getSimpleName();
+    private static final CameraLogger LOG = CameraLogger.create(TAG);
+
     public final static int PERMISSION_REQUEST_CODE = 16;
 
     final static int DEFAULT_JPEG_QUALITY = 100;
@@ -215,7 +217,7 @@ public class CameraView extends FrameLayout {
     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
         Size previewSize = getPreviewSize();
         if (previewSize == null) {
-            Log.e(TAG, "onMeasure, surface is not ready. Calling default behavior.");
+            LOG.w("onMeasure:", "surface is not ready. Calling default behavior.");
             super.onMeasure(widthMeasureSpec, heightMeasureSpec);
             return;
         }
@@ -234,18 +236,18 @@ public class CameraView extends FrameLayout {
         final ViewGroup.LayoutParams lp = getLayoutParams();
         if (widthMode == AT_MOST && lp.width == MATCH_PARENT) widthMode = EXACTLY;
         if (heightMode == AT_MOST && lp.height == MATCH_PARENT) heightMode = EXACTLY;
-        Log.e(TAG, "onMeasure, requested dimensions are (" +
+        LOG.i("onMeasure:", "requested dimensions are",
-                widthValue + "[" + ms(widthMode) + "]x" +
+                "(" + widthValue + "[" + ms(widthMode) + "]x" +
                 heightValue + "[" + ms(heightMode) + "])");
-        Log.e(TAG, "onMeasure, previewSize is (" + previewWidth + "x" + previewHeight + ")");
+        LOG.i("onMeasure:",  "previewSize is", "(" + previewWidth + "x" + previewHeight + ")");
 
 
         // If we have fixed dimensions (either 300dp or MATCH_PARENT), there's nothing we should do,
         // other than respect it. The preview will eventually be cropped at the sides (by PreviewImpl scaling)
         // except the case in which these fixed dimensions manage to fit exactly the preview aspect ratio.
         if (widthMode == EXACTLY && heightMode == EXACTLY) {
-            Log.e(TAG, "onMeasure, both are MATCH_PARENT or fixed value. We adapt. This means CROP_INSIDE. " +
+            LOG.w("onMeasure:", "both are MATCH_PARENT or fixed value. We adapt.",
-                    "(" + widthValue + "x" + heightValue + ")");
+                    "This means CROP_CENTER.", "(" + widthValue + "x" + heightValue + ")");
             super.onMeasure(widthMeasureSpec, heightMeasureSpec);
             return;
         }
@@ -253,8 +255,8 @@ public class CameraView extends FrameLayout {
         // If both dimensions are free, with no limits, then our size will be exactly the
         // preview size. This can happen rarely, for example in scrollable containers.
         if (widthMode == UNSPECIFIED && heightMode == UNSPECIFIED) {
-            Log.e(TAG, "onMeasure, both are completely free. " +
+            LOG.i("onMeasure:", "both are completely free.",
-                    "We respect that and extend to the whole preview size. " +
+                    "We respect that and extend to the whole preview size.",
                     "(" + previewWidth + "x" + previewHeight + ")");
             super.onMeasure(
                     MeasureSpec.makeMeasureSpec((int) previewWidth, EXACTLY),
@@ -279,7 +281,7 @@ public class CameraView extends FrameLayout {
                 width = widthValue;
                 height = (int) (width * ratio);
             }
-            Log.e(TAG, "onMeasure, one dimension was free, we adapted it to fit the aspect ratio. " +
+            LOG.i("onMeasure:", "one dimension was free, we adapted it to fit the aspect ratio.",
                     "(" + width + "x" + height + ")");
             super.onMeasure(MeasureSpec.makeMeasureSpec(width, EXACTLY),
                     MeasureSpec.makeMeasureSpec(height, EXACTLY));
@@ -299,8 +301,9 @@ public class CameraView extends FrameLayout {
                 width = widthValue;
                 height = Math.min((int) (width * ratio), heightValue);
             }
-            Log.e(TAG, "onMeasure, one dimension was EXACTLY, another AT_MOST. We have TRIED to fit " +
+            LOG.i("onMeasure:", "one dimension was EXACTLY, another AT_MOST.",
-                    "the aspect ratio, but it's not guaranteed. (" + width + "x" + height + ")");
+                    "We have TRIED to fit the aspect ratio, but it's not guaranteed.",
+                    "(" + width + "x" + height + ")");
             super.onMeasure(MeasureSpec.makeMeasureSpec(width, EXACTLY),
                     MeasureSpec.makeMeasureSpec(height, EXACTLY));
             return;
@@ -318,7 +321,8 @@ public class CameraView extends FrameLayout {
             height = heightValue;
             width = (int) (height / ratio);
         }
-        Log.e(TAG, "onMeasure, both dimension were AT_MOST. We fit the preview aspect ratio. " +
+        LOG.i("onMeasure:", "both dimension were AT_MOST.",
+                "We fit the preview aspect ratio.",
                 "(" + width + "x" + height + ")");
         super.onMeasure(MeasureSpec.makeMeasureSpec(width, EXACTLY),
                 MeasureSpec.makeMeasureSpec(height, EXACTLY));
@@ -406,13 +410,13 @@ public class CameraView extends FrameLayout {
         // Pass to our own GestureLayouts
         CameraOptions options = mCameraController.getCameraOptions(); // Non null
         if (mPinchGestureLayout.onTouchEvent(event)) {
-            // Log.e(TAG, "pinch!");
+            LOG.i("onTouchEvent", "pinch!");
             onGesture(mPinchGestureLayout, options);
         } else if (mScrollGestureLayout.onTouchEvent(event)) {
-            // Log.e(TAG, "scroll!");
+            LOG.i("onTouchEvent", "scroll!");
             onGesture(mScrollGestureLayout, options);
         } else if (mTapGestureLayout.onTouchEvent(event)) {
-            // Log.e(TAG, "tap!");
+            LOG.i("onTouchEvent", "tap!");
             onGesture(mTapGestureLayout, options);
         }
         return true;
@@ -545,10 +549,9 @@ public class CameraView extends FrameLayout {
                         return;
                     }
                 }
-                String message = "When the session type is set to video, the RECORD_AUDIO permission " +
+                LOG.e("Permission error:", "When the session type is set to video,",
-                        "should be added to the application manifest file.";
+                        "the RECORD_AUDIO permission should be added to the app manifest file.");
-                Log.w(TAG, message);
+                throw new IllegalStateException(CameraLogger.lastMessage);
-                throw new IllegalStateException(message);
             } catch (PackageManager.NameNotFoundException e) {
                 // Not possible.
             }
@@ -1217,6 +1220,7 @@ public class CameraView extends FrameLayout {
 
         // Outer listeners
         private ArrayList<CameraListener> mListeners = new ArrayList<>(2);
+        private CameraLogger mLogger = CameraLogger.create(CameraCallbacks.class.getSimpleName());
 
         // Orientation TODO: move this logic into OrientationHelper
         private Integer mDisplayOffset;
@@ -1226,6 +1230,7 @@ public class CameraView extends FrameLayout {
 
 
         public void dispatchOnCameraOpened(final CameraOptions options) {
+            mLogger.i("dispatchOnCameraOpened", options);
             mUiHandler.post(new Runnable() {
                 @Override
                 public void run() {
@@ -1238,6 +1243,7 @@ public class CameraView extends FrameLayout {
 
 
         public void dispatchOnCameraClosed() {
+            mLogger.i("dispatchOnCameraClosed");
             mUiHandler.post(new Runnable() {
                 @Override
                 public void run() {
@@ -1250,6 +1256,7 @@ public class CameraView extends FrameLayout {
 
 
         public void onCameraPreviewSizeChanged() {
+            mLogger.i("onCameraPreviewSizeChanged");
             // Camera preview size, as returned by getPreviewSize(), has changed.
             // Request a layout pass for onMeasure() to do its stuff.
             // Potentially this will change CameraView size, which changes Surface size,
@@ -1281,6 +1288,7 @@ public class CameraView extends FrameLayout {
          *                         because it was taken with the front camera.
          */
         public void processImage(final byte[] jpeg, final boolean consistentWithView, final boolean flipHorizontally) {
+            mLogger.i("processImage");
             mWorkerHandler.post(new Runnable() {
                 @Override
                 public void run() {
@@ -1291,8 +1299,8 @@ public class CameraView extends FrameLayout {
                         int w = consistentWithView ? getWidth() : getHeight();
                         int h = consistentWithView ? getHeight() : getWidth();
                         AspectRatio targetRatio = AspectRatio.of(w, h);
-                        // Log.e(TAG, "is Consistent? " + consistentWithView);
+                        mLogger.i("processImage", "is consistent?", consistentWithView);
-                        // Log.e(TAG, "viewWidth? " + getWidth() + ", viewHeight? " + getHeight());
+                        mLogger.i("processImage", "viewWidth?", getWidth(), "viewHeight?", getHeight());
                         jpeg2 = CropHelper.cropToJpeg(jpeg, targetRatio, mJpegQuality);
                     }
                     dispatchOnPictureTaken(jpeg2);
@@ -1302,6 +1310,7 @@ public class CameraView extends FrameLayout {
 
 
         public void processSnapshot(final YuvImage yuv, final boolean consistentWithView, boolean flipHorizontally) {
+            mLogger.i("processSnapshot");
             mWorkerHandler.post(new Runnable() {
                 @Override
                 public void run() {
@@ -1310,6 +1319,8 @@ public class CameraView extends FrameLayout {
                         int w = consistentWithView ? getWidth() : getHeight();
                         int h = consistentWithView ? getHeight() : getWidth();
                         AspectRatio targetRatio = AspectRatio.of(w, h);
+                        mLogger.i("processSnapshot", "is consistent?", consistentWithView);
+                        mLogger.i("processSnapshot", "viewWidth?", getWidth(), "viewHeight?", getHeight());
                         jpeg = CropHelper.cropToJpeg(yuv, targetRatio, mJpegQuality);
                     } else {
                         ByteArrayOutputStream out = new ByteArrayOutputStream();
@@ -1323,6 +1334,7 @@ public class CameraView extends FrameLayout {
 
 
         private void dispatchOnPictureTaken(byte[] jpeg) {
+            mLogger.i("dispatchOnPictureTaken");
             final byte[] data = jpeg;
             mUiHandler.post(new Runnable() {
                 @Override
@@ -1336,6 +1348,7 @@ public class CameraView extends FrameLayout {
 
 
         public void dispatchOnVideoTaken(final File video) {
+            mLogger.i("dispatchOnVideoTaken", video);
             mUiHandler.post(new Runnable() {
                 @Override
                 public void run() {
@@ -1348,6 +1361,7 @@ public class CameraView extends FrameLayout {
 
 
         public void dispatchOnFocusStart(@Nullable final Gesture gesture, final PointF point) {
+            mLogger.i("dispatchOnFocusStart", gesture, point);
             mUiHandler.post(new Runnable() {
                 @Override
                 public void run() {
@@ -1365,6 +1379,7 @@ public class CameraView extends FrameLayout {
 
         public void dispatchOnFocusEnd(@Nullable final Gesture gesture, final boolean success,
                                        final PointF point) {
+            mLogger.i("dispatchOnFocusEnd", gesture, success, point);
             mUiHandler.post(new Runnable() {
                 @Override
                 public void run() {
@@ -1386,6 +1401,7 @@ public class CameraView extends FrameLayout {
 
         @Override
         public void onDisplayOffsetChanged(int displayOffset) {
+            mLogger.i("onDisplayOffsetChanged", displayOffset);
             mCameraController.onDisplayOffset(displayOffset);
             mDisplayOffset = displayOffset;
             if (mDeviceOrientation != null) {
@@ -1396,6 +1412,7 @@ public class CameraView extends FrameLayout {
 
         @Override
         public void onDeviceOrientationChanged(int deviceOrientation) {
+            mLogger.i("onDeviceOrientationChanged", deviceOrientation);
             mCameraController.onDeviceOrientation(deviceOrientation);
             mDeviceOrientation = deviceOrientation;
             if (mDisplayOffset != null) {
@@ -1406,6 +1423,7 @@ public class CameraView extends FrameLayout {
 
 
         private void dispatchOnOrientationChanged(final int value) {
+            mLogger.i("dispatchOnOrientationChanged", value);
             mUiHandler.post(new Runnable() {
                 @Override
                 public void run() {
@@ -1418,6 +1436,7 @@ public class CameraView extends FrameLayout {
 
 
         public void dispatchOnZoomChanged(final float newValue, final PointF[] fingers) {
+            mLogger.i("dispatchOnZoomChanged", newValue);
             mUiHandler.post(new Runnable() {
                 @Override
                 public void run() {
@@ -1432,6 +1451,7 @@ public class CameraView extends FrameLayout {
         public void dispatchOnExposureCorrectionChanged(final float newValue,
                                                         final float[] bounds,
                                                         final PointF[] fingers) {
+            mLogger.i("dispatchOnExposureCorrectionChanged", newValue);
             mUiHandler.post(new Runnable() {
                 @Override
                 public void run() {
@@ -1444,16 +1464,19 @@ public class CameraView extends FrameLayout {
 
 
         private void addListener(@NonNull CameraListener cameraListener) {
+            mLogger.i("addListener");
             mListeners.add(cameraListener);
         }
 
 
         private void removeListener(@NonNull CameraListener cameraListener) {
+            mLogger.i("removeListener");
             mListeners.remove(cameraListener);
         }
 
 
         private void clearListeners() {
+            mLogger.i("clearListeners");
             mListeners.clear();
         }
     }

cameraview/src/main/utils/com/otaliastudios/cameraview/CameraLogger.java

@@ -0,0 +1,92 @@
+package com.otaliastudios.cameraview;
+
+import android.support.annotation.IntDef;
+import android.util.Log;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+/**
+ * Utility class that can log traces and info.
+ */
+public final class CameraLogger {
+
+    public final static int LEVEL_VERBOSE = 0;
+    public final static int LEVEL_WARNING = 1;
+    public final static int LEVEL_ERROR = 2;
+
+    @IntDef({LEVEL_VERBOSE, LEVEL_WARNING, LEVEL_ERROR})
+    @Retention(RetentionPolicy.SOURCE)
+    @interface LogLevel {}
+
+    private static int level = LEVEL_ERROR;
+
+    public static void setLogLevel(int logLevel) {
+        level = logLevel;
+    }
+
+    static String lastMessage;
+    static String lastTag;
+
+    static CameraLogger create(String tag) {
+        return new CameraLogger(tag);
+    }
+
+    private String mTag;
+
+    private CameraLogger(String tag) {
+        mTag = tag;
+    }
+
+    public void i(String message) {
+        if (should(LEVEL_VERBOSE)) {
+            Log.i(mTag, message);
+            lastMessage = message;
+            lastTag = mTag;
+        }
+    }
+
+    public void w(String message) {
+        if (should(LEVEL_WARNING)) {
+            Log.w(mTag, message);
+            lastMessage = message;
+            lastTag = mTag;
+        }
+    }
+
+    public void e(String message) {
+        if (should(LEVEL_ERROR)) {
+            Log.w(mTag, message);
+            lastMessage = message;
+            lastTag = mTag;
+        }
+    }
+
+    private boolean should(int messageLevel) {
+        return level <= messageLevel;
+    }
+
+    private String string(int messageLevel, Object... ofData) {
+        String message = "";
+        if (should(messageLevel)) {
+            for (Object o : ofData) {
+                message += String.valueOf(o);
+                message += " ";
+            }
+        }
+        return message.trim();
+    }
+
+    public void i(Object... data) {
+        i(string(LEVEL_VERBOSE, data));
+    }
+
+    public void w(Object... data) {
+        w(string(LEVEL_WARNING, data));
+    }
+
+    public void e(Object... data) {
+        e(string(LEVEL_ERROR, data));
+    }
+}
+

cameraview/src/main/views/com/otaliastudios/cameraview/ScrollGestureLayout.java

@@ -14,6 +14,8 @@ import android.widget.ImageView;
 
 class ScrollGestureLayout extends GestureLayout {
 
+    private static final String TAG = ScrollGestureLayout.class.getSimpleName();
+    private static final CameraLogger LOG = CameraLogger.create(TAG);
 
     private GestureDetector mDetector;
     private boolean mNotify;
@@ -33,7 +35,7 @@ class ScrollGestureLayout extends GestureLayout {
             @Override
             public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
                 boolean horizontal;
-                // Log.e("ScrollGestureLayout", "onScroll, distanceX="+distanceX+", distanceY="+distanceY);
+                LOG.i("onScroll:", "distanceX="+distanceX, "distanceY="+distanceY);
                 if (e1.getX() != mPoints[0].x || e1.getY() != mPoints[0].y) {
                     // First step. We choose now if it's a vertical or horizontal scroll, and
                     // stick to it for the whole gesture.
@@ -71,7 +73,7 @@ class ScrollGestureLayout extends GestureLayout {
         mDetector.onTouchEvent(event);
 
         // Keep notifying CameraView as long as the gesture goes.
-        // if (mNotify) Log.e("ScrollGestureLayout", "notifying a gesture "+mType.name());
+        if (mNotify) LOG.i("Notifying a gesture of type", mType.name());
         return mNotify;
     }
 
@@ -91,7 +93,7 @@ class ScrollGestureLayout extends GestureLayout {
         float newValue = currValue + delta;
         if (newValue < minValue) newValue = minValue;
         if (newValue > maxValue) newValue = maxValue;
-        // Log.e("ScrollGestureLayout", "curr="+currValue+", min="+minValue+", max="+maxValue+", out="+newValue);
+        LOG.i("curr="+currValue, "min="+minValue, "max="+maxValue, "out="+newValue);
         return newValue;
     }
 

demo/src/main/java/com/otaliastudios/cameraview/demo/MainActivity.java

@@ -15,6 +15,7 @@ import android.widget.TextView;
 import android.widget.Toast;
 
 import com.otaliastudios.cameraview.CameraListener;
+import com.otaliastudios.cameraview.CameraLogger;
 import com.otaliastudios.cameraview.CameraView;
 import com.otaliastudios.cameraview.Grid;
 import com.otaliastudios.cameraview.SessionType;
@@ -83,6 +84,7 @@ public class MainActivity extends AppCompatActivity implements View.OnLayoutChan
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         ButterKnife.bind(this);
+        CameraLogger.setLogLevel(CameraLogger.LEVEL_VERBOSE);
 
         parent.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
             @Override