Enable overriding ActionBar alpha value

library/src/com/manuelpeinado/fadingactionbar/FadingActionBarHelperBase.java

@@ -58,6 +58,7 @@ public abstract class FadingActionBarHelperBase {
     private boolean mFirstGlobalLayoutPerformed;
     private FrameLayout mMarginView;
     private View mListViewBackgroundView;
+    private int mActionBarAlpha = 255;
 
     public final <T extends FadingActionBarHelperBase> T actionBarBackground(int drawableResId) {
         mActionBarBackgroundResId = drawableResId;
@@ -173,7 +174,16 @@ public void initActionBar(Activity activity) {
         if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.JELLY_BEAN) {
             mActionBarBackgroundDrawable.setCallback(mDrawableCallback);
         }
-        mActionBarBackgroundDrawable.setAlpha(0);
+        setActionBarAlpha(0);
+    }
+
+    public int getActionbarAlpha(){
+        return mActionBarAlpha;
+    }
+
+    public void setActionBarAlpha(int alpha){
+        mActionBarBackgroundDrawable.setAlpha(alpha);
+        mActionBarAlpha = alpha;
     }
 
     protected abstract int getActionBarHeight();
@@ -310,7 +320,7 @@ private void onNewScroll(int scrollPosition) {
         int headerHeight = currentHeaderHeight - getActionBarHeight();
         float ratio = (float) Math.min(Math.max(scrollPosition, 0), headerHeight) / headerHeight;
         int newAlpha = (int) (ratio * 255);
-        mActionBarBackgroundDrawable.setAlpha(newAlpha);
+        setActionBarAlpha(newAlpha);
 
         addParallaxEffect(scrollPosition);
     }

samples/stock/res/layout/activity_navigation_drawer.xml

@@ -18,14 +18,21 @@
          The drawer is given a fixed width in dp and extends the full height of
          the container. A solid background is used for contrast
          with the content view. -->
-    <ListView
+    <LinearLayout
         android:id="@+id/left_drawer"
         android:paddingTop="?android:attr/actionBarSize"
         android:layout_width="240dp"
         android:layout_height="match_parent"
-        android:layout_gravity="start"
-        android:choiceMode="singleChoice"
-        android:divider="@android:color/transparent"
-        android:dividerHeight="0dp"
-        android:background="#111"/>
+        android:layout_gravity="start">
+
+        <ListView
+            android:id="@+id/left_drawer_list"
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"
+            android:choiceMode="singleChoice"
+            android:divider="@android:color/transparent"
+            android:dividerHeight="0dp"
+            android:background="#111"/>
+
+    </LinearLayout>
 </android.support.v4.widget.DrawerLayout>

samples/stock/src/com/manuelpeinado/fadingactionbar/demo/NavigationDrawerActivity.java

@@ -29,13 +29,20 @@
 import android.view.View;
 import android.widget.AdapterView;
 import android.widget.ArrayAdapter;
+import android.widget.LinearLayout;
 import android.widget.ListView;
 
 public class NavigationDrawerActivity extends Activity implements AdapterView.OnItemClickListener {
 
     private DrawerLayout mDrawerLayout;
+    private LinearLayout mDrawer;
     private ListView mDrawerList;
     private ActionBarDrawerToggle mDrawerToggle;
+    private ActionBarHolder mActionbarHolder;
+
+    private boolean mDrawerIsOpen = false;
+    private int mDrawerState = DrawerLayout.STATE_IDLE;
+    private int mOldAlpha = 0;
 
     private CharSequence mDrawerTitle;
     private CharSequence mTitle;
@@ -56,7 +63,8 @@ protected void onCreate(Bundle savedInstanceState) {
         }
         typedArray.recycle();
         mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
-        mDrawerList = (ListView) findViewById(R.id.left_drawer);
+        mDrawer = (LinearLayout) findViewById(R.id.left_drawer);
+        mDrawerList = (ListView) findViewById(R.id.left_drawer_list);
 
         // set a custom shadow that overlays the main content when the drawer opens
         mDrawerLayout.setDrawerShadow(R.drawable.drawer_shadow, GravityCompat.START);
@@ -80,10 +88,31 @@ protected void onCreate(Bundle savedInstanceState) {
         ) {
             public void onDrawerClosed(View view) {
                 getActionBar().setTitle(mTitle);
+                mDrawerIsOpen = false;
             }
 
             public void onDrawerOpened(View drawerView) {
                 getActionBar().setTitle(mDrawerTitle);
+                mDrawerIsOpen = true;
+            }
+
+            public void onDrawerStateChanged(int newState) {
+                super.onDrawerStateChanged(newState);
+
+                if (!mDrawerIsOpen && mDrawerState == DrawerLayout.STATE_IDLE && mActionbarHolder != null) {
+                    mOldAlpha = mActionbarHolder.getAlpha();
+                }
+
+                mDrawerState = newState;
+            }
+
+            public void onDrawerSlide(View drawerView, float slideOffset) {
+                super.onDrawerSlide(drawerView, slideOffset);
+
+                if (mActionbarHolder != null) {
+                    int newAlpha = Math.round(mOldAlpha + ((255 - mOldAlpha) * slideOffset));
+                    mActionbarHolder.overrideAlpha(newAlpha);
+                }
             }
         };
 
@@ -131,15 +160,26 @@ private void selectItem(int position) {
         FragmentManager fragmentManager = getFragmentManager();
         fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();
 
+        mActionbarHolder = (ActionBarHolder) fragment;
+        mOldAlpha = 0;
+
         // update selected item and title, then close the drawer
         mDrawerList.setItemChecked(position, true);
         setTitle(mCityNames[position]);
-        mDrawerLayout.closeDrawer(mDrawerList);
+        mDrawerLayout.closeDrawer(mDrawer);
     }
 
     @Override
     public void setTitle(CharSequence title) {
         mTitle = title;
         getActionBar().setTitle(mTitle);
     }
+
+    public interface ActionBarHolder {
+
+        public void overrideAlpha(int alpha);
+
+        public int getAlpha();
+    }
+
 }

samples/stock/src/com/manuelpeinado/fadingactionbar/demo/SampleFragment.java

@@ -26,7 +26,7 @@
 
 import com.manuelpeinado.fadingactionbar.FadingActionBarHelper;
 
-public class SampleFragment extends Fragment {
+public class SampleFragment extends Fragment implements NavigationDrawerActivity.ActionBarHolder {
     private FadingActionBarHelper mFadingHelper;
     private Bundle mArguments;
 
@@ -59,4 +59,20 @@ public void onAttach(Activity activity) {
             .lightActionBar(actionBarBg == R.drawable.ab_background_light);
         mFadingHelper.initActionBar(activity);
     }
+
+    @Override
+    public void overrideAlpha(int alpha) {
+        if (mFadingHelper != null){
+            mFadingHelper.setActionBarAlpha(alpha);
+        }
+    }
+
+    @Override
+    public int getAlpha(){
+        if (mFadingHelper != null){
+            return mFadingHelper.getActionbarAlpha();
+        } else {
+            return 0;
+        }
+    }
 }