FragmentPagerAdapter.java revision 5c1637087453de15e31861f073eae5133c4e9f7b 
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.view.PagerAdapter;
24import android.util.Log;
25import android.view.View;
26
27/**
28 * Implementation of {@link android.support.v4.view.PagerAdapter} that
29 * represents each page as a {@link android.app.Fragment} that is persistently
30 * kept in the fragment manager as long as the user can return to the page.
31 */
32public abstract class FragmentPagerAdapter extends PagerAdapter {
33    private static final String TAG = "FragmentPagerAdapter";
34    private static final boolean DEBUG = false;
35
36    private final FragmentManager mFragmentManager;
37    private FragmentTransaction mCurTransaction = null;
38
39    public FragmentPagerAdapter(FragmentManager fm) {
40        mFragmentManager = fm;
41    }
42
43    /**
44     * Return the Fragment associated with a specified position.
45     */
46    public abstract Fragment getItem(int position);
47
48    @Override
49    public void startUpdate(View container) {
50    }
51
52    @Override
53    public Object instantiateItem(View container, int position) {
54        if (mCurTransaction == null) {
55            mCurTransaction = mFragmentManager.beginTransaction();
56        }
57
58        // Do we already have this fragment?
59        String name = makeFragmentName(container.getId(), position);
60        Fragment fragment = mFragmentManager.findFragmentByTag(name);
61        if (fragment != null) {
62            if (DEBUG) Log.v(TAG, "Attaching item #" + position + ": f=" + fragment);
63            mCurTransaction.attach(fragment);
64        } else {
65            fragment = getItem(position);
66            if (DEBUG) Log.v(TAG, "Adding item #" + position + ": f=" + fragment);
67            mCurTransaction.add(container.getId(), fragment,
68                    makeFragmentName(container.getId(), position));
69        }
70
71        return fragment;
72    }
73
74    @Override
75    public void destroyItem(View container, int position, Object object) {
76        if (mCurTransaction == null) {
77            mCurTransaction = mFragmentManager.beginTransaction();
78        }
79        if (DEBUG) Log.v(TAG, "Detaching item #" + position + ": f=" + object
80                + " v=" + ((Fragment)object).getView());
81        mCurTransaction.detach((Fragment)object);
82    }
83
84    @Override
85    public void finishUpdate(View container) {
86        if (mCurTransaction != null) {
87            mCurTransaction.commit();
88            mCurTransaction = null;
89            mFragmentManager.executePendingTransactions();
90        }
91    }
92
93    @Override
94    public boolean isViewFromObject(View view, Object object) {
95        return ((Fragment)object).getView() == view;
96    }
97
98    @Override
99    public Parcelable saveState() {
100        return null;
101    }
102
103    @Override
104    public void restoreState(Parcelable state, ClassLoader loader) {
105    }
106
107    private static String makeFragmentName(int viewId, int index) {
108        return "android:switcher:" + viewId + ":" + index;
109    }
110}