1/*
2 * Copyright 2018 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 androidx.fragment.app;
18
19import android.os.Bundle;
20import android.os.Parcelable;
21import android.util.Log;
22import android.view.View;
23import android.view.ViewGroup;
24
25import androidx.viewpager.widget.PagerAdapter;
26
27import java.util.ArrayList;
28
29/**
30 * Implementation of {@link PagerAdapter} that
31 * uses a {@link Fragment} to manage each page. This class also handles
32 * saving and restoring of fragment's state.
33 *
34 * <p>This version of the pager is more useful when there are a large number
35 * of pages, working more like a list view.  When pages are not visible to
36 * the user, their entire fragment may be destroyed, only keeping the saved
37 * state of that fragment.  This allows the pager to hold on to much less
38 * memory associated with each visited page as compared to
39 * {@link FragmentPagerAdapter} at the cost of potentially more overhead when
40 * switching between pages.
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 frameworks/support/samples/Support13Demos/src/main/java/com/example/android/supportv13/app/FragmentStatePagerSupport.java
52 *      complete}
53 *
54 * <p>The <code>R.layout.fragment_pager</code> resource of the top-level fragment is:
55 *
56 * {@sample frameworks/support/samples/Support13Demos/src/main/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 frameworks/support/samples/Support13Demos/src/main/res/layout/fragment_pager_list.xml
63 *      complete}
64 */
65public abstract class FragmentStatePagerAdapter extends PagerAdapter {
66    private static final String TAG = "FragmentStatePagerAdapt";
67    private static final boolean DEBUG = false;
68
69    private final FragmentManager mFragmentManager;
70    private FragmentTransaction mCurTransaction = null;
71
72    private ArrayList<Fragment.SavedState> mSavedState = new ArrayList<Fragment.SavedState>();
73    private ArrayList<Fragment> mFragments = new ArrayList<Fragment>();
74    private Fragment mCurrentPrimaryItem = null;
75
76    public FragmentStatePagerAdapter(FragmentManager fm) {
77        mFragmentManager = fm;
78    }
79
80    /**
81     * Return the Fragment associated with a specified position.
82     */
83    public abstract Fragment getItem(int position);
84
85    @Override
86    public void startUpdate(ViewGroup container) {
87        if (container.getId() == View.NO_ID) {
88            throw new IllegalStateException("ViewPager with adapter " + this
89                    + " requires a view id");
90        }
91    }
92
93    @Override
94    public Object instantiateItem(ViewGroup container, int position) {
95        // If we already have this item instantiated, there is nothing
96        // to do.  This can happen when we are restoring the entire pager
97        // from its saved state, where the fragment manager has already
98        // taken care of restoring the fragments we previously had instantiated.
99        if (mFragments.size() > position) {
100            Fragment f = mFragments.get(position);
101            if (f != null) {
102                return f;
103            }
104        }
105
106        if (mCurTransaction == null) {
107            mCurTransaction = mFragmentManager.beginTransaction();
108        }
109
110        Fragment fragment = getItem(position);
111        if (DEBUG) Log.v(TAG, "Adding item #" + position + ": f=" + fragment);
112        if (mSavedState.size() > position) {
113            Fragment.SavedState fss = mSavedState.get(position);
114            if (fss != null) {
115                fragment.setInitialSavedState(fss);
116            }
117        }
118        while (mFragments.size() <= position) {
119            mFragments.add(null);
120        }
121        fragment.setMenuVisibility(false);
122        fragment.setUserVisibleHint(false);
123        mFragments.set(position, fragment);
124        mCurTransaction.add(container.getId(), fragment);
125
126        return fragment;
127    }
128
129    @Override
130    public void destroyItem(ViewGroup container, int position, Object object) {
131        Fragment fragment = (Fragment) object;
132
133        if (mCurTransaction == null) {
134            mCurTransaction = mFragmentManager.beginTransaction();
135        }
136        if (DEBUG) Log.v(TAG, "Removing item #" + position + ": f=" + object
137                + " v=" + ((Fragment)object).getView());
138        while (mSavedState.size() <= position) {
139            mSavedState.add(null);
140        }
141        mSavedState.set(position, fragment.isAdded()
142                ? mFragmentManager.saveFragmentInstanceState(fragment) : null);
143        mFragments.set(position, null);
144
145        mCurTransaction.remove(fragment);
146    }
147
148    @Override
149    @SuppressWarnings("ReferenceEquality")
150    public void setPrimaryItem(ViewGroup container, int position, Object object) {
151        Fragment fragment = (Fragment)object;
152        if (fragment != mCurrentPrimaryItem) {
153            if (mCurrentPrimaryItem != null) {
154                mCurrentPrimaryItem.setMenuVisibility(false);
155                mCurrentPrimaryItem.setUserVisibleHint(false);
156            }
157            if (fragment != null) {
158                fragment.setMenuVisibility(true);
159                fragment.setUserVisibleHint(true);
160            }
161            mCurrentPrimaryItem = fragment;
162        }
163    }
164
165    @Override
166    public void finishUpdate(ViewGroup container) {
167        if (mCurTransaction != null) {
168            mCurTransaction.commitNowAllowingStateLoss();
169            mCurTransaction = null;
170        }
171    }
172
173    @Override
174    public boolean isViewFromObject(View view, Object object) {
175        return ((Fragment)object).getView() == view;
176    }
177
178    @Override
179    public Parcelable saveState() {
180        Bundle state = null;
181        if (mSavedState.size() > 0) {
182            state = new Bundle();
183            Fragment.SavedState[] fss = new Fragment.SavedState[mSavedState.size()];
184            mSavedState.toArray(fss);
185            state.putParcelableArray("states", fss);
186        }
187        for (int i=0; i<mFragments.size(); i++) {
188            Fragment f = mFragments.get(i);
189            if (f != null && f.isAdded()) {
190                if (state == null) {
191                    state = new Bundle();
192                }
193                String key = "f" + i;
194                mFragmentManager.putFragment(state, key, f);
195            }
196        }
197        return state;
198    }
199
200    @Override
201    public void restoreState(Parcelable state, ClassLoader loader) {
202        if (state != null) {
203            Bundle bundle = (Bundle)state;
204            bundle.setClassLoader(loader);
205            Parcelable[] fss = bundle.getParcelableArray("states");
206            mSavedState.clear();
207            mFragments.clear();
208            if (fss != null) {
209                for (int i=0; i<fss.length; i++) {
210                    mSavedState.add((Fragment.SavedState)fss[i]);
211                }
212            }
213            Iterable<String> keys = bundle.keySet();
214            for (String key: keys) {
215                if (key.startsWith("f")) {
216                    int index = Integer.parseInt(key.substring(1));
217                    Fragment f = mFragmentManager.getFragment(bundle, key);
218                    if (f != null) {
219                        while (mFragments.size() <= index) {
220                            mFragments.add(null);
221                        }
222                        f.setMenuVisibility(false);
223                        mFragments.set(index, f);
224                    } else {
225                        Log.w(TAG, "Bad fragment at key " + key);
226                    }
227                }
228            }
229        }
230    }
231}
232