Java tutorial
/* * Copyright (C) 2011 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.nononsenseapps.support.app; import com.nononsenseapps.helpers.Log; import com.nononsenseapps.notepad.core.R; import android.annotation.TargetApi; import android.app.Fragment; import android.app.FragmentManager; import android.app.FragmentTransaction; import android.content.Context; import android.os.Parcelable; import android.support.v4.view.PagerAdapter; import android.view.View; import android.view.ViewGroup; /** * Implementation of {@link android.support.v4.view.PagerAdapter} that * represents each page as a {@link Fragment} that is persistently kept in the * fragment manager as long as the user can return to the page. * * <p> * This version of the pager is best for use when there are a handful of * typically more static fragments to be paged through, such as a set of tabs. * The fragment of each page the user visits will be kept in memory, though its * view hierarchy may be destroyed when not visible. This can result in using a * significant amount of memory since fragment instances can hold on to an * arbitrary amount of state. For larger sets of pages, consider * {@link FragmentStatePagerAdapter}. * * <p> * When using FragmentPagerAdapter the host ViewPager must have a valid ID set. * </p> * * <p> * Subclasses only need to implement {@link #getItem(int)} and * {@link #getCount()} to have a working adapter. * * <p> * Here is an example implementation of a pager containing fragments of lists: * * {@sample * development/samples/Support4Demos/src/com/example/android/supportv4/app/ * FragmentPagerSupport.java complete} * * <p> * The <code>R.layout.fragment_pager</code> resource of the top-level fragment * is: * * {@sample development/samples/Support4Demos/res/layout/fragment_pager.xml * complete} * * <p> * The <code>R.layout.fragment_pager_list</code> resource containing each * individual fragment's layout is: * * {@sample development/samples/Support4Demos/res/layout/fragment_pager_list.xml * complete} */ public abstract class FragmentPagerAdapter extends PagerAdapter { private static final String TAG = "FragmentPagerAdapter"; private final FragmentManager mFragmentManager; private FragmentTransaction mCurTransaction = null; private Fragment mCurrentPrimaryItem = null; private final Context context; public Fragment getCurrentPrimaryItem() { return mCurrentPrimaryItem; } public FragmentPagerAdapter(Context context, FragmentManager fm) { this.context = context; mFragmentManager = fm; } /** * Return the Fragment associated with a specified position. */ public abstract Fragment getItem(int position); // @Override // public void startUpdate(ViewGroup container) { // // } @Override public Object instantiateItem(ViewGroup container, int position) { if (mCurTransaction == null) { mCurTransaction = mFragmentManager.beginTransaction(); } final long itemId = getItemId(position); // Do we already have this fragment? String name = makeFragmentName(container.getId(), itemId); Fragment fragment = mFragmentManager.findFragmentByTag(name); if (fragment != null) { Log.d(TAG, "Attaching item #" + itemId + ": f=" + fragment); mCurTransaction.attach(fragment); } else { fragment = getItem(position); Log.d(TAG, "Adding item #" + itemId + ": f=" + fragment); mCurTransaction.add(container.getId(), fragment, makeFragmentName(container.getId(), itemId)); } // if (fragment != mCurrentPrimaryItem) { setMenuVisibility(fragment, false); setUserVisibleHint(fragment, false); // } return fragment; } @Override public void destroyItem(ViewGroup container, int position, Object object) { if (mCurTransaction == null) { mCurTransaction = mFragmentManager.beginTransaction(); } Log.d(TAG, "Detaching item #" + getItemId(position) + ": f=" + object + " v=" + ((Fragment) object).getView()); mCurTransaction.detach((Fragment) object); } @TargetApi(14) private void setMenuVisibility(final Fragment fragment, final boolean value) { if (fragment != null && context.getResources().getBoolean(R.bool.atLeast14)) fragment.setMenuVisibility(value); } @TargetApi(15) private void setUserVisibleHint(final Fragment fragment, final boolean value) { if (fragment != null && context.getResources().getBoolean(R.bool.atLeast15)) fragment.setUserVisibleHint(value); } @Override public void setPrimaryItem(ViewGroup container, int position, Object object) { Fragment fragment = (Fragment) object; if (fragment != mCurrentPrimaryItem) { if (mCurrentPrimaryItem != null) { setMenuVisibility(mCurrentPrimaryItem, false); setUserVisibleHint(mCurrentPrimaryItem, false); } if (fragment != null) { setMenuVisibility(fragment, true); setUserVisibleHint(fragment, true); } mCurrentPrimaryItem = fragment; } } @Override public void finishUpdate(ViewGroup container) { if (mCurTransaction != null) { mCurTransaction.commitAllowingStateLoss(); mCurTransaction = null; mFragmentManager.executePendingTransactions(); } } @Override public boolean isViewFromObject(View view, Object object) { return ((Fragment) object).getView() == view; } @Override public Parcelable saveState() { return null; } @Override public void restoreState(Parcelable state, ClassLoader loader) { } /** * Return a unique identifier for the item at the given position. * * <p> * The default implementation returns the given position. Subclasses should * override this method if the positions of items can change. * </p> * * @param position * Position within this adapter * @return Unique identifier for the item at position */ public abstract long getItemId(int position); private static String makeFragmentName(int viewId, long id) { return "android:switcher:" + viewId + ":" + id; } }