1/*
2 * Copyright (C) 2011 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
17package android.support.v13.app;
18
19import android.app.Fragment;
20import android.app.FragmentManager;
21import android.app.FragmentTransaction;
22import android.os.Parcelable;
23import android.support.v4.app.FragmentStatePagerAdapter;
24import android.support.v4.view.PagerAdapter;
25import android.util.Log;
26import android.view.View;
27import android.view.ViewGroup;
28
29/**
30 * Implementation of {@link android.support.v4.view.PagerAdapter} that
31 * represents each page as a {@link android.app.Fragment} that is persistently
32 * kept in the fragment manager as long as the user can return to the page.
33 *
34 * <p>This version of the pager is best for use when there are a handful of
35 * typically more static fragments to be paged through, such as a set of tabs.
36 * The fragment of each page the user visits will be kept in memory, though its
37 * view hierarchy may be destroyed when not visible.  This can result in using
38 * a significant amount of memory since fragment instances can hold on to an
39 * arbitrary amount of state.  For larger sets of pages, consider
40 * {@link FragmentStatePagerAdapter}.
41 *
42 * <p>When using FragmentPagerAdapter the host ViewPager must have a
43 * valid ID set.</p>
44 *
45 * <p>Subclasses only need to implement {@link #getItem(int)}
46 * and {@link #getCount()} to have a working adapter.
47 *
48 * <p>Here is an example implementation of a pager containing fragments of
49 * lists:
50 *
51 * {@sample development/samples/Support13Demos/src/com/example/android/supportv13/app/FragmentPagerSupport.java
52 *      complete}
53 *
54 * <p>The <code>R.layout.fragment_pager</code> resource of the top-level fragment is:
55 *
56 * {@sample development/samples/Support13Demos/res/layout/fragment_pager.xml
57 *      complete}
58 *
59 * <p>The <code>R.layout.fragment_pager_list</code> resource containing each
60 * individual fragment's layout is:
61 *
62 * {@sample development/samples/Support13Demos/res/layout/fragment_pager_list.xml
63 *      complete}
64 */
65public abstract class FragmentPagerAdapter extends PagerAdapter {
66    private static final String TAG = "FragmentPagerAdapter";
67    private static final boolean DEBUG = false;
68
69    private final FragmentManager mFragmentManager;
70    private FragmentTransaction mCurTransaction = null;
71    private Fragment mCurrentPrimaryItem = null;
72
73    public FragmentPagerAdapter(FragmentManager fm) {
74        mFragmentManager = fm;
75    }
76
77    /**
78     * Return the Fragment associated with a specified position.
79     */
80    public abstract Fragment getItem(int position);
81
82    @Override
83    public void startUpdate(ViewGroup container) {
84    }
85
86    @Override
87    public Object instantiateItem(ViewGroup container, int position) {
88        if (mCurTransaction == null) {
89            mCurTransaction = mFragmentManager.beginTransaction();
90        }
91
92        final long itemId = getItemId(position);
93
94        // Do we already have this fragment?
95        String name = makeFragmentName(container.getId(), itemId);
96        Fragment fragment = mFragmentManager.findFragmentByTag(name);
97        if (fragment != null) {
98            if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
99            mCurTransaction.attach(fragment);
100        } else {
101            fragment = getItem(position);
102            if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
103            mCurTransaction.add(container.getId(), fragment,
104                    makeFragmentName(container.getId(), itemId));
105        }
106        if (fragment != mCurrentPrimaryItem) {
107            FragmentCompat.setMenuVisibility(fragment, false);
108            FragmentCompat.setUserVisibleHint(fragment, false);
109        }
110
111        return fragment;
112    }
113
114    @Override
115    public void destroyItem(ViewGroup container, int position, Object object) {
116        if (mCurTransaction == null) {
117            mCurTransaction = mFragmentManager.beginTransaction();
118        }
119        if (DEBUG) Log.v(TAG, "Detaching item #" + getItemId(position) + ": f=" + object
120                + " v=" + ((Fragment)object).getView());
121        mCurTransaction.detach((Fragment)object);
122    }
123
124    @Override
125    public void setPrimaryItem(ViewGroup container, int position, Object object) {
126        Fragment fragment = (Fragment)object;
127        if (fragment != mCurrentPrimaryItem) {
128            if (mCurrentPrimaryItem != null) {
129                FragmentCompat.setMenuVisibility(mCurrentPrimaryItem, false);
130                FragmentCompat.setUserVisibleHint(mCurrentPrimaryItem, false);
131            }
132            if (fragment != null) {
133                FragmentCompat.setMenuVisibility(fragment, true);
134                FragmentCompat.setUserVisibleHint(fragment, true);
135            }
136            mCurrentPrimaryItem = fragment;
137        }
138    }
139
140    @Override
141    public void finishUpdate(ViewGroup container) {
142        if (mCurTransaction != null) {
143            mCurTransaction.commitAllowingStateLoss();
144            mCurTransaction = null;
145            mFragmentManager.executePendingTransactions();
146        }
147    }
148
149    @Override
150    public boolean isViewFromObject(View view, Object object) {
151        return ((Fragment)object).getView() == view;
152    }
153
154    @Override
155    public Parcelable saveState() {
156        return null;
157    }
158
159    @Override
160    public void restoreState(Parcelable state, ClassLoader loader) {
161    }
162
163    /**
164     * Return a unique identifier for the item at the given position.
165     *
166     * <p>The default implementation returns the given position.
167     * Subclasses should override this method if the positions of items can change.</p>
168     *
169     * @param position Position within this adapter
170     * @return Unique identifier for the item at position
171     */
172    public long getItemId(int position) {
173        return position;
174    }
175
176    private static String makeFragmentName(int viewId, long id) {
177        return "android:switcher:" + viewId + ":" + id;
178    }
179}