FragmentPagerAdapter.java revision abc968f1eba800c34a4008deb43b015da5d23a5f 
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;
23
24/**
25 * Implementation of {@link android.support.v4.view.PagerAdapter} that
26 * represents each page as a {@link Fragment} that is persistently
27 * kept in the fragment manager as long as the user can return to the page.
28 */
29public abstract class FragmentPagerAdapter extends PagerAdapter {
30    private static final String TAG = "FragmentPagerAdapter";
31    private static final boolean DEBUG = false;
32
33    private final FragmentManager mFragmentManager;
34    private FragmentTransaction mCurTransaction = null;
35    private Fragment mCurrentPrimaryItem = null;
36
37    public FragmentPagerAdapter(FragmentManager fm) {
38        mFragmentManager = fm;
39    }
40
41    /**
42     * Return the Fragment associated with a specified position.
43     */
44    public abstract Fragment getItem(int position);
45
46    @Override
47    public void startUpdate(View container) {
48    }
49
50    @Override
51    public Object instantiateItem(View container, int position) {
52        if (mCurTransaction == null) {
53            mCurTransaction = mFragmentManager.beginTransaction();
54        }
55
56        // Do we already have this fragment?
57        String name = makeFragmentName(container.getId(), position);
58        Fragment fragment = mFragmentManager.findFragmentByTag(name);
59        if (fragment != null) {
60            if (DEBUG) Log.v(TAG, "Attaching item #" + position + ": f=" + fragment);
61            mCurTransaction.attach(fragment);
62        } else {
63            fragment = getItem(position);
64            if (DEBUG) Log.v(TAG, "Adding item #" + position + ": f=" + fragment);
65            mCurTransaction.add(container.getId(), fragment,
66                    makeFragmentName(container.getId(), position));
67        }
68        if (fragment != mCurrentPrimaryItem) {
69            fragment.setMenuVisibility(false);
70            fragment.setStartDeferred(true);
71        }
72
73        return fragment;
74    }
75
76    @Override
77    public void destroyItem(View container, int position, Object object) {
78        if (mCurTransaction == null) {
79            mCurTransaction = mFragmentManager.beginTransaction();
80        }
81        if (DEBUG) Log.v(TAG, "Detaching item #" + position + ": f=" + object
82                + " v=" + ((Fragment)object).getView());
83        mCurTransaction.detach((Fragment)object);
84    }
85
86    @Override
87    public void setPrimaryItem(View container, int position, Object object) {
88        Fragment fragment = (Fragment)object;
89        if (fragment != mCurrentPrimaryItem) {
90            if (mCurrentPrimaryItem != null) {
91                mCurrentPrimaryItem.setMenuVisibility(false);
92                mCurrentPrimaryItem.setStartDeferred(true);
93            }
94            if (fragment != null) {
95                fragment.setMenuVisibility(true);
96                fragment.setStartDeferred(false);
97            }
98            mCurrentPrimaryItem = fragment;
99        }
100    }
101
102    @Override
103    public void finishUpdate(View container) {
104        if (mCurTransaction != null) {
105            mCurTransaction.commitAllowingStateLoss();
106            mCurTransaction = null;
107            mFragmentManager.executePendingTransactions();
108        }
109    }
110
111    @Override
112    public boolean isViewFromObject(View view, Object object) {
113        return ((Fragment)object).getView() == view;
114    }
115
116    @Override
117    public Parcelable saveState() {
118        return null;
119    }
120
121    @Override
122    public void restoreState(Parcelable state, ClassLoader loader) {
123    }
124
125    private static String makeFragmentName(int viewId, int index) {
126        return "android:switcher:" + viewId + ":" + index;
127    }
128}
129