Fixed incorrect visibilities of mini FABs for stopwatch page

app/src/main/java/com/philliphsu/clock2/BaseFragment.java

@@ -39,4 +39,15 @@ public abstract class BaseFragment extends Fragment {
         super.onDestroyView();
         ButterKnife.unbind(this); // Only for fragments!
     }
+
+    /**
+     * Callback invoked when this Fragment is part of a ViewPager and it has been
+     * selected, as indicated by {@link android.support.v4.view.ViewPager.OnPageChangeListener#onPageSelected(int)
+     * onPageSelected(int)}.
+     */
+    public void onPageSelected() {
+        // TODO: Consider making this abstract. The reason it wasn't abstract in the first place
+        // is not all Fragments in our ViewPager need to do things upon being selected. As such,
+        // those Fragments' classes would just end up stubbing this implementation.
+    }
 }

app/src/main/java/com/philliphsu/clock2/MainActivity.java

@@ -122,6 +122,10 @@ public class MainActivity extends BaseActivity {
                 if (position < mSectionsPagerAdapter.getCount() - 1) {
                     mFab.setImageDrawable(mAddItemDrawable);
                 }
+                Fragment f = mSectionsPagerAdapter.getFragment(mViewPager.getCurrentItem());
+                if (f instanceof BaseFragment) {
+                    ((BaseFragment) f).onPageSelected();
+                }
             }
 //            @Override
 //            public void onPageScrollStateChanged(int state) {

app/src/main/java/com/philliphsu/clock2/stopwatch/StopwatchFragment.java

@@ -99,23 +99,10 @@ public class StopwatchFragment extends RecyclerViewFragment<
         }
         // Hides the mini fabs prematurely, so when we actually display this tab
         // they won't show even briefly at all before hiding.
-        updateButtonControls();
+//        updateButtonControls();
         return view;
     }
 
-    @Override
-    public void onResume() {
-        super.onResume();
-        // FAB icon change won't happen when selecting this tab from multiple tabs away,
-        // because isResumed() and isVisible() both return false, respectively from
-        // setUserVisibleHint() and from updateButtonControls() when called by onCreateView().
-        // TODO: Since this is only called to change the FAB icon, just allow duplicate
-        // code and manipulate the FAB directly.
-        // TODO: This has the side effect of prematurely changing the icon for the
-        // page directly before this page.
-        updateButtonControls();
-    }
-
     /**
      * If the user navigates away, this is the furthest point in the lifecycle
      * this Fragment gets to. Here, the view hierarchy returned from onCreateView()
@@ -212,26 +199,8 @@ public class StopwatchFragment extends RecyclerViewFragment<
     }
 
     @Override
-    public void setUserVisibleHint(boolean isVisibleToUser) {
-        super.setUserVisibleHint(isVisibleToUser);
-        // We get called multiple times, even when we're not yet visible.
-        // This can be called before onCreateView() so widgets could be null, esp. if you had
-        // navigated more than one page away before returning here. That means onDestroyView()
-        // was called previously.
-        // We will get called again when we actually have this page selected, and by that time
-        // onCreateView() will have been called. Wait until we're resumed to call through.
-        if (isVisibleToUser && isResumed()) {
-            Log.d(TAG, "setUserVisibleHint called thru");
-            // At this point, the only thing this does is change the fab icon
-            // TODO: allow duplicate code and manipulate the fab icon directly?
-            // TODO: There is noticeable latency between showing this tab and
-            // changing the icon. Consider writing a callback for this Fragment
-            // that MainActivity can call in its onPageChangeListener. We don't merely
-            // want to call such a callback in onPageSelected, because that is fired
-            // when we reach an idle state, so we'd experience the same latency issue.
-            // Rather, we should animate the icon change during onPageScrolled.
-            updateButtonControls();
-        }
+    public void onPageSelected() {
+        updateButtonControls();
     }
 
     @Nullable
@@ -296,8 +265,9 @@ public class StopwatchFragment extends RecyclerViewFragment<
         int vis = started ? View.VISIBLE : View.INVISIBLE;
         mNewLapButton.setVisibility(vis);
         mStopButton.setVisibility(vis);
+        // TODO: We no longer call this method in lifecycle events where we aren't actually
+        // resumed/visible, so we can remove this check.
         if (isVisible()) { // avoid changing the icon prematurely, esp. when we're not on this tab
-            Log.d(TAG, "Fab icon changing");
             mActivityFab.get().setImageDrawable(mChronometer.isRunning() ? mPauseDrawable : mStartDrawable);
         }
     }

app/src/main/res/layout/fragment_stopwatch.xml

@@ -46,6 +46,7 @@
             android:layout_height="wrap_content"
             android:src="@drawable/ic_half_day_1_black_24dp"
             android:tint="@android:color/white"
+            android:visibility="invisible"
             app:layout_columnWeight="1"
             app:layout_gravity="center"
             app:fabSize="mini"
@@ -57,6 +58,7 @@
             android:layout_height="wrap_content"
             android:src="@drawable/ic_stop_24dp"
             android:tint="@android:color/white"
+            android:visibility="invisible"
             app:layout_columnWeight="1"
             app:layout_gravity="center"
             app:fabSize="mini"