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.Bundle;
23import android.os.Parcelable;
24import android.support.v4.app.FragmentPagerAdapter;
25import android.support.v4.view.PagerAdapter;
26import android.util.Log;
27import android.view.View;
28import android.view.ViewGroup;
29
30import java.util.ArrayList;
31
32/**
33 * Implementation of {@link android.support.v4.view.PagerAdapter} that
34 * uses a {@link Fragment} to manage each page. This class also handles
35 * saving and restoring of fragment's state.
36 *
37 * <p>This version of the pager is more useful when there are a large number
38 * of pages, working more like a list view.  When pages are not visible to
39 * the user, their entire fragment may be destroyed, only keeping the saved
40 * state of that fragment.  This allows the pager to hold on to much less
41 * memory associated with each visited page as compared to
42 * {@link FragmentPagerAdapter} at the cost of potentially more overhead when
43 * switching between pages.
44 *
45 * <p>When using FragmentPagerAdapter the host ViewPager must have a
46 * valid ID set.</p>
47 *
48 * <p>Subclasses only need to implement {@link #getItem(int)}
49 * and {@link #getCount()} to have a working adapter.
50 *
51 * <p>Here is an example implementation of a pager containing fragments of
52 * lists:
53 *
54 * {@sample development/samples/Support4Demos/src/com/example/android/supportv4/app/FragmentStatePagerSupport.java
55 *      complete}
56 *
57 * <p>The <code>R.layout.fragment_pager</code> resource of the top-level fragment is:
58 *
59 * {@sample development/samples/Support4Demos/res/layout/fragment_pager.xml
60 *      complete}
61 *
62 * <p>The <code>R.layout.fragment_pager_list</code> resource containing each
63 * individual fragment's layout is:
64 *
65 * {@sample development/samples/Support4Demos/res/layout/fragment_pager_list.xml
66 *      complete}
67 */
68public abstract class FragmentStatePagerAdapter extends PagerAdapter {
69    private static final String TAG = "FragmentStatePagerAdapter";
70    private static final boolean DEBUG = false;
71
72    private final FragmentManager mFragmentManager;
73    private FragmentTransaction mCurTransaction = null;
74
75    private ArrayList<Fragment.SavedState> mSavedState = new ArrayList<Fragment.SavedState>();
76    private ArrayList<Fragment> mFragments = new ArrayList<Fragment>();
77    private Fragment mCurrentPrimaryItem = null;
78
79    public FragmentStatePagerAdapter(FragmentManager fm) {
80        mFragmentManager = fm;
81    }
82
83    /**
84     * Return the Fragment associated with a specified position.
85     */
86    public abstract Fragment getItem(int position);
87
88    @Override
89    public void startUpdate(ViewGroup container) {
90    }
91
92    @Override
93    public Object instantiateItem(ViewGroup container, int position) {
94        // If we already have this item instantiated, there is nothing
95        // to do.  This can happen when we are restoring the entire pager
96        // from its saved state, where the fragment manager has already
97        // taken care of restoring the fragments we previously had instantiated.
98        if (mFragments.size() > position) {
99            Fragment f = mFragments.get(position);
100            if (f != null) {
101                return f;
102            }
103        }
104
105        if (mCurTransaction == null) {
106            mCurTransaction = mFragmentManager.beginTransaction();
107        }
108
109        Fragment fragment = getItem(position);
110        if (DEBUG) Log.v(TAG, "Adding item #" + position + ": f=" + fragment);
111        if (mSavedState.size() > position) {
112            Fragment.SavedState fss = mSavedState.get(position);
113            if (fss != null) {
114                fragment.setInitialSavedState(fss);
115            }
116        }
117        while (mFragments.size() <= position) {
118            mFragments.add(null);
119        }
120        FragmentCompat.setMenuVisibility(fragment, false);
121        FragmentCompat.setUserVisibleHint(fragment, false);
122        mFragments.set(position, fragment);
123        mCurTransaction.add(container.getId(), fragment);
124
125        return fragment;
126    }
127
128    @Override
129    public void destroyItem(ViewGroup container, int position, Object object) {
130        Fragment fragment = (Fragment)object;
131
132        if (mCurTransaction == null) {
133            mCurTransaction = mFragmentManager.beginTransaction();
134        }
135        if (DEBUG) Log.v(TAG, "Removing item #" + position + ": f=" + object
136                + " v=" + ((Fragment)object).getView());
137        while (mSavedState.size() <= position) {
138            mSavedState.add(null);
139        }
140        mSavedState.set(position, mFragmentManager.saveFragmentInstanceState(fragment));
141        mFragments.set(position, null);
142
143        mCurTransaction.remove(fragment);
144    }
145
146    @Override
147    public void setPrimaryItem(ViewGroup container, int position, Object object) {
148        Fragment fragment = (Fragment)object;
149        if (fragment != mCurrentPrimaryItem) {
150            if (mCurrentPrimaryItem != null) {
151                FragmentCompat.setMenuVisibility(mCurrentPrimaryItem, false);
152                FragmentCompat.setUserVisibleHint(mCurrentPrimaryItem, false);
153            }
154            if (fragment != null) {
155                FragmentCompat.setMenuVisibility(fragment, true);
156                FragmentCompat.setUserVisibleHint(fragment, true);
157            }
158            mCurrentPrimaryItem = fragment;
159        }
160    }
161
162    @Override
163    public void finishUpdate(ViewGroup container) {
164        if (mCurTransaction != null) {
165            mCurTransaction.commitAllowingStateLoss();
166            mCurTransaction = null;
167            mFragmentManager.executePendingTransactions();
168        }
169    }
170
171    @Override
172    public boolean isViewFromObject(View view, Object object) {
173        return ((Fragment)object).getView() == view;
174    }
175
176    @Override
177    public Parcelable saveState() {
178        Bundle state = null;
179        if (mSavedState.size() > 0) {
180            state = new Bundle();
181            Fragment.SavedState[] fss = new Fragment.SavedState[mSavedState.size()];
182            mSavedState.toArray(fss);
183            state.putParcelableArray("states", fss);
184        }
185        for (int i=0; i<mFragments.size(); i++) {
186            Fragment f = mFragments.get(i);
187            if (f != null) {
188                if (state == null) {
189                    state = new Bundle();
190                }
191                String key = "f" + i;
192                mFragmentManager.putFragment(state, key, f);
193            }
194        }
195        return state;
196    }
197
198    @Override
199    public void restoreState(Parcelable state, ClassLoader loader) {
200        if (state != null) {
201            Bundle bundle = (Bundle)state;
202            bundle.setClassLoader(loader);
203            Parcelable[] fss = bundle.getParcelableArray("states");
204            mSavedState.clear();
205            mFragments.clear();
206            if (fss != null) {
207                for (int i=0; i<fss.length; i++) {
208                    mSavedState.add((Fragment.SavedState)fss[i]);
209                }
210            }
211            Iterable<String> keys = bundle.keySet();
212            for (String key: keys) {
213                if (key.startsWith("f")) {
214                    int index = Integer.parseInt(key.substring(1));
215                    Fragment f = mFragmentManager.getFragment(bundle, key);
216                    if (f != null) {
217                        while (mFragments.size() <= index) {
218                            mFragments.add(null);
219                        }
220                        FragmentCompat.setMenuVisibility(f, false);
221                        mFragments.set(index, f);
222                    } else {
223                        Log.w(TAG, "Bad fragment at key " + key);
224                    }
225                }
226            }
227        }
228    }
229}
230