FragmentPagerAdapter.java revision 7dc96cc2410f551eefaa973ddc144146ad72d1ec 
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        // Do we already have this fragment?
93        String name = makeFragmentName(container.getId(), position);
94        Fragment fragment = mFragmentManager.findFragmentByTag(name);
95        if (fragment != null) {
96            if (DEBUG) Log.v(TAG, "Attaching item #" + position + ": f=" + fragment);
97            mCurTransaction.attach(fragment);
98        } else {
99            fragment = getItem(position);
100            if (DEBUG) Log.v(TAG, "Adding item #" + position + ": f=" + fragment);
101            mCurTransaction.add(container.getId(), fragment,
102                    makeFragmentName(container.getId(), position));
103        }
104        if (fragment != mCurrentPrimaryItem) {
105            FragmentCompat.setMenuVisibility(fragment, false);
106            FragmentCompat.setUserVisibleHint(fragment, false);
107        }
108
109        return fragment;
110    }
111
112    @Override
113    public void destroyItem(ViewGroup container, int position, Object object) {
114        if (mCurTransaction == null) {
115            mCurTransaction = mFragmentManager.beginTransaction();
116        }
117        if (DEBUG) Log.v(TAG, "Detaching item #" + position + ": f=" + object
118                + " v=" + ((Fragment)object).getView());
119        mCurTransaction.detach((Fragment)object);
120    }
121
122    @Override
123    public void setPrimaryItem(ViewGroup container, int position, Object object) {
124        Fragment fragment = (Fragment)object;
125        if (fragment != mCurrentPrimaryItem) {
126            if (mCurrentPrimaryItem != null) {
127                FragmentCompat.setMenuVisibility(mCurrentPrimaryItem, false);
128                FragmentCompat.setUserVisibleHint(mCurrentPrimaryItem, false);
129            }
130            if (fragment != null) {
131                FragmentCompat.setMenuVisibility(fragment, true);
132                FragmentCompat.setUserVisibleHint(fragment, true);
133            }
134            mCurrentPrimaryItem = fragment;
135        }
136    }
137
138    @Override
139    public void finishUpdate(ViewGroup container) {
140        if (mCurTransaction != null) {
141            mCurTransaction.commitAllowingStateLoss();
142            mCurTransaction = null;
143            mFragmentManager.executePendingTransactions();
144        }
145    }
146
147    @Override
148    public boolean isViewFromObject(View view, Object object) {
149        return ((Fragment)object).getView() == view;
150    }
151
152    @Override
153    public Parcelable saveState() {
154        return null;
155    }
156
157    @Override
158    public void restoreState(Parcelable state, ClassLoader loader) {
159    }
160
161    private static String makeFragmentName(int viewId, int index) {
162        return "android:switcher:" + viewId + ":" + index;
163    }
164}