Settings ViewPager now correctly handles RTL mode

Previously, the settings and support tabs were incorrectly orderded,
and had inverted transitions on click and on swipe.
Ordering of tabs now correctly displays All Settings as the default,
right tab, and the Support tab to its left. The tab headers also now
function properly in transition, and onclick.

Change-Id: Iab499ee13433cb78941bc33cbb0e99ffe2937174
Fixes: 30079049

src/com/android/settings/widget/RtlCompatibleViewPager.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.widget;
+
+import android.content.Context;
+import android.support.v4.view.ViewPager;
+import android.text.TextUtils;
+import android.util.AttributeSet;
+import android.view.View;
+
+import java.util.Locale;
+
+/**
+ * A {@link ViewPager} that's aware of RTL changes when used with FragmentPagerAdapter.
+ */
+public final class RtlCompatibleViewPager extends ViewPager {
+
+    /**
+     * Callback interface for responding to changing state of the selected page.
+     * Positions supplied will always be the logical position in the adapter -
+     * that is, the 0 index corresponds to the left-most page in LTR and the
+     * right-most page in RTL.
+     */
+
+    public RtlCompatibleViewPager(Context context) {
+        this(context, null /* attrs */);
+    }
+
+    public RtlCompatibleViewPager(Context context, AttributeSet attrs) {
+        super(context, attrs);
+    }
+
+    @Override
+    public int getCurrentItem() {
+        return getRtlAwareIndex(super.getCurrentItem());
+    }
+
+    @Override
+    public void setCurrentItem(int item) {
+        super.setCurrentItem(getRtlAwareIndex(item));
+    }
+
+    /**
+     * Get a "RTL friendly" index. If the locale is LTR, the index is returned as is.
+     * Otherwise it's transformed so view pager can render views using the new index for RTL. For
+     * example, the second view will be rendered to the left of first view.
+     *
+     * @param index The logical index.
+     */
+    public int getRtlAwareIndex(int index) {
+        // Using TextUtils rather than View.getLayoutDirection() because LayoutDirection is not
+        // defined until onMeasure, and this is called before then.
+        if (TextUtils.getLayoutDirectionFromLocale(Locale.getDefault())
+                == View.LAYOUT_DIRECTION_RTL) {
+            return getAdapter().getCount() - index - 1;
+        }
+        return index;
+    }
+}

src/com/android/settings/widget/SlidingTabLayout.java

@@ -18,7 +18,6 @@ package com.android.settings.widget;
 
 import android.content.Context;
 import android.support.v4.view.PagerAdapter;
-import android.support.v4.view.ViewPager;
 import android.util.AttributeSet;
 import android.view.Gravity;
 import android.view.LayoutInflater;
@@ -39,7 +38,7 @@ public final class SlidingTabLayout extends FrameLayout implements View.OnClickL
     private final View mIndicatorView;
     private final LayoutInflater mLayoutInflater;
 
-    private ViewPager mViewPager;
+    private RtlCompatibleViewPager mViewPager;
     private int mSelectedPosition;
     private float mSelectionOffset;
 
@@ -58,7 +57,7 @@ public final class SlidingTabLayout extends FrameLayout implements View.OnClickL
      * Sets the associated view pager. Note that the assumption here is that the pager content
      * (number of tabs and tab titles) does not change after this call has been made.
      */
-    public void setViewPager(ViewPager viewPager) {
+    public void setViewPager(RtlCompatibleViewPager viewPager) {
         mTitleView.removeAllViews();
 
         mViewPager = viewPager;
@@ -87,8 +86,19 @@ public final class SlidingTabLayout extends FrameLayout implements View.OnClickL
             mTitleView.layout(0, 0, mTitleView.getMeasuredWidth(), mTitleView.getMeasuredHeight());
             final int indicatorBottom = getMeasuredHeight();
             final int indicatorHeight = mIndicatorView.getMeasuredHeight();
-            mIndicatorView.layout(0, indicatorBottom - indicatorHeight,
-                    mIndicatorView.getMeasuredWidth(), indicatorBottom);
+            final int indicatorWidth = mIndicatorView.getMeasuredWidth();
+            final int totalWidth = getMeasuredWidth();
+
+            // IndicatorView should start on the right when RTL mode is enabled
+            if (isRtlMode()) {
+                mIndicatorView.layout(totalWidth - indicatorWidth,
+                        indicatorBottom - indicatorHeight, totalWidth,
+                        indicatorBottom);
+            } else {
+
+                mIndicatorView.layout(0, indicatorBottom - indicatorHeight,
+                        indicatorWidth, indicatorBottom);
+            }
         }
     }
 
@@ -106,7 +116,9 @@ public final class SlidingTabLayout extends FrameLayout implements View.OnClickL
     private void onViewPagerPageChanged(int position, float positionOffset) {
         mSelectedPosition = position;
         mSelectionOffset = positionOffset;
-        mIndicatorView.setTranslationX(getIndicatorLeft());
+        // Translation should be reversed in RTL mode
+        final int leftIndicator = isRtlMode() ? -getIndicatorLeft() : getIndicatorLeft();
+        mIndicatorView.setTranslationX(leftIndicator);
     }
 
     private void populateTabStrip() {
@@ -135,7 +147,12 @@ public final class SlidingTabLayout extends FrameLayout implements View.OnClickL
         return left;
     }
 
-    private final class InternalViewPagerListener implements ViewPager.OnPageChangeListener {
+    private boolean isRtlMode() {
+        return getLayoutDirection() == LAYOUT_DIRECTION_RTL;
+    }
+
+    private final class InternalViewPagerListener implements
+            RtlCompatibleViewPager.OnPageChangeListener {
         private int mScrollState;
 
         @Override
@@ -154,7 +171,8 @@ public final class SlidingTabLayout extends FrameLayout implements View.OnClickL
 
         @Override
         public void onPageSelected(int position) {
-            if (mScrollState == ViewPager.SCROLL_STATE_IDLE) {
+            position = mViewPager.getRtlAwareIndex(position);
+            if (mScrollState == RtlCompatibleViewPager.SCROLL_STATE_IDLE) {
                 onViewPagerPageChanged(position, 0f);
             }
             final int titleCount = mTitleView.getChildCount();