Added underscroll tracking within ForecastFragment for elevation control.

app/src/main/java/com/example/android/sunshine/app/ForecastFragment.java

@@ -25,10 +25,13 @@ import android.net.Uri;
 import android.os.Build;
 import android.os.Bundle;
 import android.preference.PreferenceManager;
+import android.support.design.widget.AppBarLayout;
+import android.support.design.widget.CoordinatorLayout;
 import android.support.v4.app.Fragment;
 import android.support.v4.app.LoaderManager;
 import android.support.v4.content.CursorLoader;
 import android.support.v4.content.Loader;
+import android.support.v4.view.ViewCompat;
 import android.support.v7.widget.LinearLayoutManager;
 import android.support.v7.widget.RecyclerView;
 import android.util.AttributeSet;
@@ -219,6 +222,24 @@ public class ForecastFragment extends Fragment implements LoaderManager.LoaderCa
             }
         }
 
+        final AppBarLayout appbarView = (AppBarLayout)rootView.findViewById(R.id.appbar);
+        if (null != appbarView) {
+            ViewCompat.setElevation(appbarView, 0);
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
+                mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
+                    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
+                    @Override
+                    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
+                        if (0 == mRecyclerView.computeVerticalScrollOffset()) {
+                            appbarView.setElevation(0);
+                        } else {
+                            appbarView.setElevation(appbarView.getTargetElevation());
+                        }
+                    }
+                });
+            }
+        }
+
         // If there's instance state, mine it for useful information.
         // The end-goal here is that the user never knows that turning their device sideways
         // does crazy lifecycle related things.  It should feel like some stuff stretched out,

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

@@ -30,7 +30,7 @@
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
-        app:elevation="0dp">
+        app:elevation="@dimen/appbar_elevation">
 
         <android.support.v7.widget.Toolbar
             android:id="@+id/toolbar"
@@ -46,11 +46,9 @@
                 android:layout_gravity="center_horizontal"
                 android:contentDescription="@string/app_name"
                 android:scaleType="center"
-                android:src="@drawable/ic_logo"
-                app:layout_scrollFlags="scroll|enterAlways" />
+                android:src="@drawable/ic_logo"/>
             </android.support.v7.widget.Toolbar>
 
-
     </android.support.design.widget.AppBarLayout>
 
     <android.support.v7.widget.RecyclerView