Add ActionBar tab callback method onTabReselected

onTabReselected is called if an already-selected tab is chosen again.
For many apps this will be a no-op, but some may treat it as a signal
to return to the top level of a given navigation category.

Change-Id: Ic51fbe477b979562f2d848c4070b2016b217a90f

api/current.xml

@@ -19972,6 +19972,21 @@
  deprecated="not deprecated"
  visibility="public"
 >
+<method name="onTabReselected"
+ return="void"
+ abstract="true"
+ native="false"
+ synchronized="false"
+ static="false"
+ final="false"
+ deprecated="not deprecated"
+ visibility="public"
+>
+<parameter name="tab" type="android.app.ActionBar.Tab">
+</parameter>
+<parameter name="ft" type="android.app.FragmentTransaction">
+</parameter>
+</method>
 <method name="onTabSelected"
  return="void"
  abstract="true"

core/java/android/app/ActionBar.java

@@ -470,5 +470,15 @@ public abstract class ActionBar {
          *        will be executed in a single transaction.
          */
         public void onTabUnselected(Tab tab, FragmentTransaction ft);
+
+        /**
+         * Called when a tab that is already selected is chosen again by the user.
+         * Some applications may use this action to return to the top level of a category.
+         *
+         * @param tab The tab that was reselected.
+         * @param ft A {@link FragmentTransaction} for queuing fragment operations to execute
+         *        once this method returns.
+         */
+        public void onTabReselected(Tab tab, FragmentTransaction ft);
     }
 }

core/java/com/android/internal/app/ActionBarImpl.java

@@ -326,18 +326,21 @@ public class ActionBarImpl extends ActionBar {
 
     @Override
     public void selectTab(Tab tab) {
-        if (mSelectedTab == tab) {
-            return;
-        }
-
-        mActionView.setTabSelected(tab != null ? tab.getPosition() : Tab.INVALID_POSITION);
         final FragmentTransaction trans = mActivity.getFragmentManager().openTransaction();
-        if (mSelectedTab != null) {
-            mSelectedTab.getCallback().onTabUnselected(mSelectedTab, trans);
-        }
-        mSelectedTab = (TabImpl) tab;
-        if (mSelectedTab != null) {
-            mSelectedTab.getCallback().onTabSelected(mSelectedTab, trans);
+
+        if (mSelectedTab == tab) {
+            if (mSelectedTab != null) {
+                mSelectedTab.getCallback().onTabReselected(mSelectedTab, trans);
+            }
+        } else {
+            mActionView.setTabSelected(tab != null ? tab.getPosition() : Tab.INVALID_POSITION);
+            if (mSelectedTab != null) {
+                mSelectedTab.getCallback().onTabUnselected(mSelectedTab, trans);
+            }
+            mSelectedTab = (TabImpl) tab;
+            if (mSelectedTab != null) {
+                mSelectedTab.getCallback().onTabSelected(mSelectedTab, trans);
+            }
         }
 
         if (!trans.isEmpty()) {