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      1 /*
      2  * Copyright (C) 2015 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.deskclock.widget;
     18 
     19 import android.content.Context;
     20 import android.support.v4.view.ViewPager;
     21 import android.text.TextUtils;
     22 import android.util.AttributeSet;
     23 import android.view.View;
     24 
     25 import java.util.Locale;
     26 
     27 /**
     28  * A {@link ViewPager} that's aware of RTL changes when used with FragmentPagerAdapter.
     29  */
     30 public final class RtlViewPager extends ViewPager {
     31 
     32     /**
     33      * Callback interface for responding to changing state of the selected page.
     34      * Positions supplied will always be the logical position in the adapter -
     35      * that is, the 0 index corresponds to the left-most page in LTR and the
     36      * right-most page in RTL.
     37      */
     38     private OnPageChangeListener mListener;
     39 
     40     public RtlViewPager(Context context) {
     41         this(context, null /* attrs */);
     42     }
     43 
     44     public RtlViewPager(Context context, AttributeSet attrs) {
     45         super(context, attrs);
     46         addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
     47             @Override
     48             public void onPageScrolled(int position, float offset, int offsetPixels) {
     49                 // Do nothing
     50             }
     51 
     52             @Override
     53             public void onPageSelected(int position) {
     54                 if (mListener != null) {
     55                     mListener.onPageSelected(getRtlAwareIndex(position));
     56                 }
     57             }
     58 
     59             @Override
     60             public void onPageScrollStateChanged(int state) {
     61                 // Do nothing
     62             }
     63         });
     64     }
     65 
     66     @Override
     67     public int getCurrentItem() {
     68         return getRtlAwareIndex(super.getCurrentItem());
     69     }
     70 
     71     @Override
     72     public void setCurrentItem(int item) {
     73         super.setCurrentItem(getRtlAwareIndex(item));
     74     }
     75 
     76     @Override
     77     public void setOnPageChangeListener(OnPageChangeListener unused) {
     78         throw new UnsupportedOperationException("Use setOnRTLPageChangeListener instead");
     79     }
     80 
     81     /**
     82      * Get a "RTL friendly" index. If the locale is LTR, the index is returned as is.
     83      * Otherwise it's transformed so view pager can render views using the new index for RTL. For
     84      * example, the second view will be rendered to the left of first view.
     85      *
     86      * @param index The logical index.
     87      */
     88     public int getRtlAwareIndex(int index) {
     89         if (TextUtils.getLayoutDirectionFromLocale(Locale.getDefault()) ==
     90                 View.LAYOUT_DIRECTION_RTL) {
     91             return getAdapter().getCount() - index - 1;
     92         }
     93         return index;
     94     }
     95 
     96     /**
     97      * Sets a {@link OnPageChangeListener}. The listener will be called when a page is selected.
     98      */
     99     public void setOnRTLPageChangeListener(OnPageChangeListener listener) {
    100         mListener = listener;
    101     }
    102 }
    103