Move the listener logic out of the Activity and into the View.

Change variable naming in ToggleScrollView to meet standard.
Cache the result of computeVerticalScrollRange() in ToggleScrollView.

src/com/fsck/k9/activity/MessageView.java

@@ -97,7 +97,6 @@ public class MessageView extends K9Activity implements OnClickListener {
     private Listener mListener = new Listener();
     private MessageViewHandler mHandler = new MessageViewHandler();
     private StorageManager.StorageListener mStorageListener = new StorageListenerImplementation();
-    private MessagingListener mLoadCompleteListener = new ScrollToLastLocationListener();
 
     /** this variable is used to save the calling AttachmentView
      *  until the onActivityResult is called.
@@ -111,11 +110,6 @@ public class MessageView extends K9Activity implements OnClickListener {
      */
     private String mDstFolder;
 
-    /**
-     * Used after restore/rotation to scroll our message to the last known location.
-     */
-    private double mScrollPercentage;
-
     private final class StorageListenerImplementation implements StorageManager.StorageListener {
         @Override
         public void onUnmount(String providerId) {
@@ -418,9 +412,8 @@ public class MessageView extends K9Activity implements OnClickListener {
 
         mMessageView.initialize(this);
 
-        // Add listener for message load completion.  We'll use this to scroll the page to user's last known
+        // Register the ScrollView's listener to handle scrolling to last known location on resume.
-        // location.
+        mController.addListener(mTopView.getListener());
-        mController.addListener(mLoadCompleteListener);
         mMessageView.setListeners(mController.getListeners());
 
         setTitle("");
@@ -430,6 +423,7 @@ public class MessageView extends K9Activity implements OnClickListener {
 
         Uri uri = intent.getData();
         if (icicle != null) {
+            // TODO This code seems unnecessary since the icicle should already be thawed in onRestoreInstanceState().
             mMessageReference = icicle.getParcelable(EXTRA_MESSAGE_REFERENCE);
             mMessageReferences = icicle.getParcelableArrayList(EXTRA_MESSAGE_REFERENCES);
             mPgpData = (PgpData) icicle.getSerializable(STATE_PGP_DATA);
@@ -543,9 +537,7 @@ public class MessageView extends K9Activity implements OnClickListener {
         outState.putParcelableArrayList(EXTRA_MESSAGE_REFERENCES, mMessageReferences);
         outState.putSerializable(STATE_PGP_DATA, mPgpData);
         outState.putBoolean(SHOW_PICTURES, mMessageView.showPictures());
-        if(mTopView != null) {
+        outState.putDouble(EXTRA_SCROLL_PERCENTAGE, mTopView.getScrollPercentage());
-            outState.putDouble(EXTRA_SCROLL_PERCENTAGE, mTopView.getScrollPercentage());
-        }
     }
 
     @Override
@@ -554,7 +546,7 @@ public class MessageView extends K9Activity implements OnClickListener {
         mPgpData = (PgpData) savedInstanceState.getSerializable(STATE_PGP_DATA);
         mMessageView.updateCryptoLayout(mAccount.getCryptoProvider(), mPgpData, mMessage);
         mMessageView.setLoadPictures(savedInstanceState.getBoolean(SHOW_PICTURES));
-        mScrollPercentage = savedInstanceState.getDouble(EXTRA_SCROLL_PERCENTAGE);
+        mTopView.setScrollPercentage(savedInstanceState.getDouble(EXTRA_SCROLL_PERCENTAGE));
     }
 
     private void displayMessage(MessageReference ref) {
@@ -674,13 +666,13 @@ public class MessageView extends K9Activity implements OnClickListener {
             onAccountUnavailable();
             return;
         }
-        mController.addListener(mLoadCompleteListener);
+        mController.addListener(mTopView.getListener());
         StorageManager.getInstance(getApplication()).addListener(mStorageListener);
     }
 
     @Override
     protected void onPause() {
-        mController.removeListener(mLoadCompleteListener);
+        mController.removeListener(mTopView.getListener());
         StorageManager.getInstance(getApplication()).removeListener(mStorageListener);
         super.onPause();
     }
@@ -893,7 +885,7 @@ public class MessageView extends K9Activity implements OnClickListener {
     @Override
     protected void onNext() {
         // Reset scroll percentage when we change messages
-        mScrollPercentage = 0;
+        mTopView.setScrollPercentage(0);
         if (mNextMessage == null) {
             Toast.makeText(this, getString(R.string.end_of_folder), Toast.LENGTH_SHORT).show();
             return;
@@ -910,7 +902,7 @@ public class MessageView extends K9Activity implements OnClickListener {
     @Override
     protected void onPrevious() {
         // Reset scroll percentage when we change messages
-        mScrollPercentage = 0;
+        mTopView.setScrollPercentage(0);
         if (mPreviousMessage == null) {
             Toast.makeText(this, getString(R.string.end_of_folder), Toast.LENGTH_SHORT).show();
             return;
@@ -1299,18 +1291,4 @@ public class MessageView extends K9Activity implements OnClickListener {
         // sometimes shows the original encrypted content
         mMessageView.loadBodyFromText(mAccount.getCryptoProvider(), mPgpData, mMessage, mPgpData.getDecryptedData(), "text/plain");
     }
-
-    /**
-     * This is a {@link MessagingListener} which listens for when the a message has finished being displayed on the
-     * screen.  We'll scroll the message to the user's last known location once it's done.
-     */
-    class ScrollToLastLocationListener extends MessagingListener {
-        public void messageViewFinished() {
-            // Don't scroll if our last position was at the top.
-            if(mTopView != null && mScrollPercentage != 0.0) {
-                Log.d(K9.LOG_TAG, "MessageView has finished loading, scrolling to last known location.");
-                mTopView.setScrollPercentage(mScrollPercentage);
-            }
-        }
-    }
 }

src/com/fsck/k9/view/ToggleScrollView.java

@@ -7,6 +7,7 @@ import android.view.GestureDetector;
 import android.view.MotionEvent;
 import android.widget.ScrollView;
 import com.fsck.k9.K9;
+import com.fsck.k9.controller.MessagingListener;
 
 /**
  * An extension of {@link ScrollView} that allows scrolling to be selectively disabled.
@@ -14,7 +15,9 @@ import com.fsck.k9.K9;
 public class ToggleScrollView extends ScrollView {
     private GestureDetector mDetector;
     private boolean mScrolling = true;
-    private int currentYPosition;
+    private int mCurrentYPosition;
+    private double mScrollPercentage;
+    private ScrollToLastLocationListener mListener;
 
     public ToggleScrollView(Context context, AttributeSet attrs) {
         super(context, attrs);
@@ -72,20 +75,23 @@ public class ToggleScrollView extends ScrollView {
      * be 100, unless the screen is of 0 height...
      */
     public double getScrollPercentage() {
-        if(computeVerticalScrollRange() == 0) {
+        // We save only the Y coordinate instead of the percentage because I don't know how expensive the
+        // computeVerticalScrollRange() call is.
+        final int scrollRange = computeVerticalScrollRange();
+        if(scrollRange == 0) {
             return 0;
         }
-        return (double)currentYPosition / computeVerticalScrollRange();
+        return (double) mCurrentYPosition / scrollRange;
     }
 
     /**
-     * Scroll the screen to a specific percentage of the page.  This is based on the top edge of the page.
+     * Set the percentage by which we should scroll the page once we get the load complete event.  This is
+     * based on the top edge of the view.
      * @param percentage Percentage of page to scroll to.
      */
     public void setScrollPercentage(final double percentage) {
-        final int newY = (int)(percentage * computeVerticalScrollRange());
+        Log.d(K9.LOG_TAG, "ToggleView: Setting last scroll percentage to " + percentage);
-        Log.d(K9.LOG_TAG, "ToggleScrollView: requested " + (100 * percentage) + "%, scrolling to " + newY + "/" + computeVerticalScrollRange());
+        this.mScrollPercentage = percentage;
-        scrollTo(0, newY);
     }
 
     /**
@@ -101,8 +107,37 @@ public class ToggleScrollView extends ScrollView {
     protected void onScrollChanged(int x, int y, int oldx, int oldy) {
         super.onScrollChanged(x, y, oldx, oldy);
 
-        this.currentYPosition = y;
+        this.mCurrentYPosition = y;
         // I wish Android has a TRACE log level so I wouldn't have to comment this out.  This one is really noisy.
-        // Log.d(K9.LOG_TAG, "ToggleScrollView: currentYPosition=" + y + " scrollRange=" + computeVerticalScrollRange() + " pct=" + getScrollPercentage());
+        // Log.d(K9.LOG_TAG, "ToggleScrollView: mCurrentYPosition=" + y + " scrollRange=" + computeVerticalScrollRange() + " pct=" + getScrollPercentage());
+    }
+
+    /**
+     * This is a {@link MessagingListener} which listens for when the a message has finished being displayed on the
+     * screen.  We'll scroll the message to the user's last known location once it's done.
+     */
+    class ScrollToLastLocationListener extends MessagingListener {
+        public void messageViewFinished() {
+            // Don't scroll if our last position was at the top.
+            if(mScrollPercentage != 0.0) {
+                final int scrollRange = computeVerticalScrollRange();
+                final int newY = (int)(mScrollPercentage * scrollRange);
+                Log.d(K9.LOG_TAG, "ToggleScrollView: requested " + (100 * mScrollPercentage) + "%, " +
+                    "scrolling to " + newY + "/" + scrollRange);
+                scrollTo(0, newY);
+            }
+        }
+    }
+
+    /**
+     * Fetch the {@link MessagingListener} for this <code>ScrollView</code>.
+     * @return
+     */
+    public MessagingListener getListener() {
+        if(this.mListener != null) {
+            return this.mListener;
+        } else {
+            return this.mListener = new ScrollToLastLocationListener();
+        }
     }
 }