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.v4.app;
18
19import android.os.Parcelable;
20import android.support.v4.view.PagerAdapter;
21import android.util.Log;
22import android.view.View;
23import android.view.ViewGroup;
24
25/**
26 * Implementation of {@link android.support.v4.view.PagerAdapter} that
27 * represents each page as a {@link Fragment} that is persistently
28 * kept in the fragment manager as long as the user can return to the page.
29 *
30 * <p>This version of the pager is best for use when there are a handful of
31 * typically more static fragments to be paged through, such as a set of tabs.
32 * The fragment of each page the user visits will be kept in memory, though its
33 * view hierarchy may be destroyed when not visible.  This can result in using
34 * a significant amount of memory since fragment instances can hold on to an
35 * arbitrary amount of state.  For larger sets of pages, consider
36 * {@link FragmentStatePagerAdapter}.
37 *
38 * <p>When using FragmentPagerAdapter the host ViewPager must have a
39 * valid ID set.</p>
40 *
41 * <p>Subclasses only need to implement {@link #getItem(int)}
42 * and {@link #getCount()} to have a working adapter.
43 *
44 * <p>Here is an example implementation of a pager containing fragments of
45 * lists:
46 *
47 * {@sample development/samples/Support4Demos/src/com/example/android/supportv4/app/FragmentPagerSupport.java
48 *      complete}
49 *
50 * <p>The <code>R.layout.fragment_pager</code> resource of the top-level fragment is:
51 *
52 * {@sample development/samples/Support4Demos/res/layout/fragment_pager.xml
53 *      complete}
54 *
55 * <p>The <code>R.layout.fragment_pager_list</code> resource containing each
56 * individual fragment's layout is:
57 *
58 * {@sample development/samples/Support4Demos/res/layout/fragment_pager_list.xml
59 *      complete}
60 */
61public abstract class FragmentPagerAdapter extends PagerAdapter {
62    private static final String TAG = "FragmentPagerAdapter";
63    private static final boolean DEBUG = false;
64
65    private final FragmentManager mFragmentManager;
66    private FragmentTransaction mCurTransaction = null;
67    private Fragment mCurrentPrimaryItem = null;
68
69    public FragmentPagerAdapter(FragmentManager fm) {
70        mFragmentManager = fm;
71    }
72
73    /**
74     * Return the Fragment associated with a specified position.
75     */
76    public abstract Fragment getItem(int position);
77
78    @Override
79    public void startUpdate(ViewGroup container) {
80        if (container.getId() == View.NO_ID) {
81            throw new IllegalStateException("ViewPager with adapter " + this
82                    + " requires a view id");
83        }
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            fragment.setMenuVisibility(false);
108            fragment.setUserVisibleHint(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                mCurrentPrimaryItem.setMenuVisibility(false);
130                mCurrentPrimaryItem.setUserVisibleHint(false);
131            }
132            if (fragment != null) {
133                fragment.setMenuVisibility(true);
134                fragment.setUserVisibleHint(true);
135            }
136            mCurrentPrimaryItem = fragment;
137        }
138    }
139
140    @Override
141    public void finishUpdate(ViewGroup container) {
142        if (mCurTransaction != null) {
143            mCurTransaction.commitNowAllowingStateLoss();
144            mCurTransaction = null;
145        }
146    }
147
148    @Override
149    public boolean isViewFromObject(View view, Object object) {
150        return ((Fragment)object).getView() == view;
151    }
152
153    @Override
154    public Parcelable saveState() {
155        return null;
156    }
157
158    @Override
159    public void restoreState(Parcelable state, ClassLoader loader) {
160    }
161
162    /**
163     * Return a unique identifier for the item at the given position.
164     *
165     * <p>The default implementation returns the given position.
166     * Subclasses should override this method if the positions of items can change.</p>
167     *
168     * @param position Position within this adapter
169     * @return Unique identifier for the item at position
170     */
171    public long getItemId(int position) {
172        return position;
173    }
174
175    private static String makeFragmentName(int viewId, long id) {
176        return "android:switcher:" + viewId + ":" + id;
177    }
178}
179