在ViewPager中替换Fragment

我试图使用片段与一个ViewPager使用FragmentPagerAdapter。我想要实现的是替换一个片段，位于ViewPager的第一页，与另一个。

寻呼机由两个页面组成。第一个是FirstPagerFragment，第二个是SecondPagerFragment。点击第一页的一个按钮。我想用NextFragment替换FirstPagerFragment。

下面是我的代码。

public class FragmentPagerActivity extends FragmentActivity {

    static final int NUM_ITEMS = 2;

    MyAdapter mAdapter;
    ViewPager mPager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fragment_pager);

        mAdapter = new MyAdapter(getSupportFragmentManager());

        mPager = (ViewPager) findViewById(R.id.pager);
        mPager.setAdapter(mAdapter);

    }


    /**
     * Pager Adapter
     */
    public static class MyAdapter extends FragmentPagerAdapter {
        public MyAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public int getCount() {
            return NUM_ITEMS;
        }

        @Override
        public Fragment getItem(int position) {

            if(position == 0) {
                return FirstPageFragment.newInstance();
            } else {
                return SecondPageFragment.newInstance();
            }

        }
    }


    /**
     * Second Page FRAGMENT
     */
    public static class SecondPageFragment extends Fragment {

        public static SecondPageFragment newInstance() {
            SecondPageFragment f = new SecondPageFragment();
            return f;
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            //Log.d("DEBUG", "onCreateView");
            return inflater.inflate(R.layout.second, container, false);

        }
    }

    /**
     * FIRST PAGE FRAGMENT
     */
    public static class FirstPageFragment extends Fragment {

        Button button;

        public static FirstPageFragment newInstance() {
            FirstPageFragment f = new FirstPageFragment();
            return f;
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            //Log.d("DEBUG", "onCreateView");
            View root = inflater.inflate(R.layout.first, container, false);
            button = (Button) root.findViewById(R.id.button);
            button.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    FragmentTransaction trans = getFragmentManager().beginTransaction();
                                    trans.replace(R.id.first_fragment_root_id, NextFragment.newInstance());
                    trans.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
                    trans.addToBackStack(null);
                    trans.commit();

                }

            });

            return root;
        }

        /**
     * Next Page FRAGMENT in the First Page
     */
    public static class NextFragment extends Fragment {

        public static NextFragment newInstance() {
            NextFragment f = new NextFragment();
            return f;
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            //Log.d("DEBUG", "onCreateView");
            return inflater.inflate(R.layout.next, container, false);

        }
    }
}

.．.这里是XML文件

fragment_pager.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical" android:padding="4dip"
        android:gravity="center_horizontal"
        android:layout_width="match_parent" android:layout_height="match_parent">

    <android.support.v4.view.ViewPager
            android:id="@+id/pager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1">
    </android.support.v4.view.ViewPager>

</LinearLayout>

first.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:id="@+id/first_fragment_root_id"
  android:orientation="vertical"
  android:layout_width="match_parent"
  android:layout_height="match_parent">

  <Button android:id="@+id/button"
     android:layout_width="wrap_content" android:layout_height="wrap_content"
     android:text="to next"/>

</LinearLayout>

现在的问题是……我应该使用哪个ID

trans.replace(R.id.first_fragment_root_id, NextFragment.newInstance());

如果我用r。id。first_fragment_root_id，替换工作，但Hierarchy Viewer显示一个奇怪的行为，如下所示。

一开始的情况是

更换后的情况是

正如你所看到的，有一些错误，我希望在替换片段后找到与第一张图片中相同的状态。

当前回答

我按照@wize和@mdelolmo的答案，我得到了解决方案。由于吨。但是，我稍微调整了这些解决方案，以提高内存消耗。

我观察到的问题:

它们保存被替换的Fragment实例。在我的情况下，它是一个持有MapView的片段，我认为它的成本很高。所以，我维护FragmentPagerPositionChanged (POSITION_NONE或POSITION_UNCHANGED)而不是Fragment本身。

这是我的实现。

  public static class DemoCollectionPagerAdapter extends FragmentStatePagerAdapter {

    private SwitchFragListener mSwitchFragListener;
    private Switch mToggle;
    private int pagerAdapterPosChanged = POSITION_UNCHANGED;
    private static final int TOGGLE_ENABLE_POS = 2;


    public DemoCollectionPagerAdapter(FragmentManager fm, Switch toggle) {
        super(fm);
        mToggle = toggle;

        mSwitchFragListener = new SwitchFragListener();
        mToggle.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                mSwitchFragListener.onSwitchToNextFragment();
            }
        });
    }

    @Override
    public Fragment getItem(int i) {
        switch (i)
        {
            case TOGGLE_ENABLE_POS:
                if(mToggle.isChecked())
                {
                    return TabReplaceFragment.getInstance();
                }else
                {
                    return DemoTab2Fragment.getInstance(i);
                }

            default:
                return DemoTabFragment.getInstance(i);
        }
    }

    @Override
    public int getCount() {
        return 5;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return "Tab " + (position + 1);
    }

    @Override
    public int getItemPosition(Object object) {

        //  This check make sures getItem() is called only for the required Fragment
        if (object instanceof TabReplaceFragment
                ||  object instanceof DemoTab2Fragment)
            return pagerAdapterPosChanged;

        return POSITION_UNCHANGED;
    }

    /**
     * Switch fragments Interface implementation
     */
    private final class SwitchFragListener implements
            SwitchFragInterface {

        SwitchFragListener() {}

        public void onSwitchToNextFragment() {

            pagerAdapterPosChanged = POSITION_NONE;
            notifyDataSetChanged();
        }
    }

    /**
     * Interface to switch frags
     */
    private interface SwitchFragInterface{
        void onSwitchToNextFragment();
    }
}

演示链接在这里..https://youtu.be/l_62uhKkLyM

出于演示目的，在位置2处使用了两个片段TabReplaceFragment和DemoTab2Fragment。在所有其他情况下，我使用DemoTabFragment实例。

解释:

我将Switch从Activity传递到DemoCollectionPagerAdapter。基于这个开关的状态，我们将显示正确的片段。当开关检查被更改时，我调用SwitchFragListener的onSwitchToNextFragment方法，其中我将pagerAdapterPosChanged变量的值更改为POSITION_NONE。查看更多关于POSITION_NONE的信息。这将使getItem无效，我有逻辑实例化正确的片段在那里。抱歉，如果解释得有点乱的话。

再次感谢@wize和@mdelolmo的原创想法。

希望这对你有帮助。：）

如果这个实现有任何缺陷，请告诉我。那将对我的项目大有帮助。

2016-06-22 05:16:54

其他回答

我已经实现了一个解决方案:

标签内的动态片段替换维护每个选项卡的历史记录处理方向变化

实现这一目标的技巧如下:

使用notifyDataSetChanged()方法来应用片段替换片段管理器只用于后台，而不用于片段替换使用纪念品模式(堆栈)维护历史记录

适配器代码如下:

public class TabsAdapter extends FragmentStatePagerAdapter implements ActionBar.TabListener, ViewPager.OnPageChangeListener {

/** The sherlock fragment activity. */
private final SherlockFragmentActivity mActivity;

/** The action bar. */
private final ActionBar mActionBar;

/** The pager. */
private final ViewPager mPager;

/** The tabs. */
private List<TabInfo> mTabs = new LinkedList<TabInfo>();

/** The total number of tabs. */
private int TOTAL_TABS;

private Map<Integer, Stack<TabInfo>> history = new HashMap<Integer, Stack<TabInfo>>();

/**
 * Creates a new instance.
 *
 * @param activity the activity
 * @param pager    the pager
 */
public TabsAdapter(SherlockFragmentActivity activity, ViewPager pager) {
    super(activity.getSupportFragmentManager());
    activity.getSupportFragmentManager();
    this.mActivity = activity;
    this.mActionBar = activity.getSupportActionBar();
    this.mPager = pager;
    mActionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
}

/**
 * Adds the tab.
 *
 * @param image         the image
 * @param fragmentClass the class
 * @param args          the arguments
 */
public void addTab(final Drawable image, final Class fragmentClass, final Bundle args) {
    final TabInfo tabInfo = new TabInfo(fragmentClass, args);
    final ActionBar.Tab tab = mActionBar.newTab();
    tab.setTabListener(this);
    tab.setTag(tabInfo);
    tab.setIcon(image);

    mTabs.add(tabInfo);
    mActionBar.addTab(tab);

    notifyDataSetChanged();
}

@Override
public Fragment getItem(final int position) {
    final TabInfo tabInfo = mTabs.get(position);
    return Fragment.instantiate(mActivity, tabInfo.fragmentClass.getName(), tabInfo.args);
}

@Override
public int getItemPosition(final Object object) {
    /* Get the current position. */
    int position = mActionBar.getSelectedTab().getPosition();

    /* The default value. */
    int pos = POSITION_NONE;
    if (history.get(position).isEmpty()) {
        return POSITION_NONE;
    }

    /* Checks if the object exists in current history. */
    for (Stack<TabInfo> stack : history.values()) {
        TabInfo c = stack.peek();
        if (c.fragmentClass.getName().equals(object.getClass().getName())) {
            pos = POSITION_UNCHANGED;
            break;
        }
    }
    return pos;
}

@Override
public int getCount() {
    return mTabs.size();
}

@Override
public void onPageScrollStateChanged(int arg0) {
}

@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
}

@Override
public void onPageSelected(int position) {
    mActionBar.setSelectedNavigationItem(position);
}

@Override
public void onTabSelected(final ActionBar.Tab tab, final FragmentTransaction ft) {
    TabInfo tabInfo = (TabInfo) tab.getTag();
    for (int i = 0; i < mTabs.size(); i++) {
        if (mTabs.get(i).equals(tabInfo)) {
            mPager.setCurrentItem(i);
        }
    }
}

@Override
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction ft) {
}

@Override
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction ft) {
}

public void replace(final int position, final Class fragmentClass, final Bundle args) {
    /* Save the fragment to the history. */
    mActivity.getSupportFragmentManager().beginTransaction().addToBackStack(null).commit();

    /* Update the tabs. */
    updateTabs(new TabInfo(fragmentClass, args), position);

    /* Updates the history. */
    history.get(position).push(new TabInfo(mTabs.get(position).fragmentClass, mTabs.get(position).args));

    notifyDataSetChanged();
}

/**
 * Updates the tabs.
 *
 * @param tabInfo
 *          the new tab info
 * @param position
 *          the position
 */
private void updateTabs(final TabInfo tabInfo, final int position) {
    mTabs.remove(position);
    mTabs.add(position, tabInfo);
    mActionBar.getTabAt(position).setTag(tabInfo);
}

/**
 * Creates the history using the current state.
 */
public void createHistory() {
    int position = 0;
    TOTAL_TABS = mTabs.size();
    for (TabInfo mTab : mTabs) {
        if (history.get(position) == null) {
            history.put(position, new Stack<TabInfo>());
        }
        history.get(position).push(new TabInfo(mTab.fragmentClass, mTab.args));
        position++;
    }
}

/**
 * Called on back
 */
public void back() {
    int position = mActionBar.getSelectedTab().getPosition();
    if (!historyIsEmpty(position)) {
        /* In case there is not any other item in the history, then finalize the activity. */
        if (isLastItemInHistory(position)) {
            mActivity.finish();
        }
        final TabInfo currentTabInfo = getPrevious(position);
        mTabs.clear();
        for (int i = 0; i < TOTAL_TABS; i++) {
            if (i == position) {
                mTabs.add(new TabInfo(currentTabInfo.fragmentClass, currentTabInfo.args));
            } else {
                TabInfo otherTabInfo = history.get(i).peek();
                mTabs.add(new TabInfo(otherTabInfo.fragmentClass, otherTabInfo.args));
            }
        }
    }
    mActionBar.selectTab(mActionBar.getTabAt(position));
    notifyDataSetChanged();
}

/**
 * Returns if the history is empty.
 *
 * @param position
 *          the position
 * @return  the flag if empty
 */
private boolean historyIsEmpty(final int position) {
    return history == null || history.isEmpty() || history.get(position).isEmpty();
}

private boolean isLastItemInHistory(final int position) {
    return history.get(position).size() == 1;
}

/**
 * Returns the previous state by the position provided.
 *
 * @param position
 *          the position
 * @return  the tab info
 */
private TabInfo getPrevious(final int position) {
    TabInfo currentTabInfo = history.get(position).pop();
    if (!history.get(position).isEmpty()) {
        currentTabInfo = history.get(position).peek();
    }
    return currentTabInfo;
}

/** The tab info class */
private static class TabInfo {

    /** The fragment class. */
    public Class fragmentClass;

    /** The args.*/
    public Bundle args;

    /**
     * Creates a new instance.
     *
     * @param fragmentClass
     *          the fragment class
     * @param args
     *          the args
     */
    public TabInfo(Class fragmentClass, Bundle args) {
        this.fragmentClass = fragmentClass;
        this.args = args;
    }

    @Override
    public boolean equals(final Object o) {
        return this.fragmentClass.getName().equals(o.getClass().getName());
    }

    @Override
    public int hashCode() {
        return fragmentClass.getName() != null ? fragmentClass.getName().hashCode() : 0;
    }

    @Override
    public String toString() {
        return "TabInfo{" +
                "fragmentClass=" + fragmentClass +
                '}';
    }
}

第一次添加所有选项卡时，我们需要调用createHistory()方法来创建初始历史记录

public void createHistory() {
    int position = 0;
    TOTAL_TABS = mTabs.size();
    for (TabInfo mTab : mTabs) {
        if (history.get(position) == null) {
            history.put(position, new Stack<TabInfo>());
        }
        history.get(position).push(new TabInfo(mTab.fragmentClass, mTab.args));
        position++;
    }
}

每次你想要替换一个片段到一个特定的标签，你调用: replace(final int position, final Class fragmentClass, final Bundle args)

/* Save the fragment to the history. */
    mActivity.getSupportFragmentManager().beginTransaction().addToBackStack(null).commit();

    /* Update the tabs. */
    updateTabs(new TabInfo(fragmentClass, args), position);

    /* Updates the history. */
    history.get(position).push(new TabInfo(mTabs.get(position).fragmentClass, mTabs.get(position).args));

    notifyDataSetChanged();

在back被按下时，你需要调用back()方法:

public void back() {
    int position = mActionBar.getSelectedTab().getPosition();
    if (!historyIsEmpty(position)) {
        /* In case there is not any other item in the history, then finalize the activity. */
        if (isLastItemInHistory(position)) {
            mActivity.finish();
        }
        final TabInfo currentTabInfo = getPrevious(position);
        mTabs.clear();
        for (int i = 0; i < TOTAL_TABS; i++) {
            if (i == position) {
                mTabs.add(new TabInfo(currentTabInfo.fragmentClass, currentTabInfo.args));
            } else {
                TabInfo otherTabInfo = history.get(i).peek();
                mTabs.add(new TabInfo(otherTabInfo.fragmentClass, otherTabInfo.args));
            }
        }
    }
    mActionBar.selectTab(mActionBar.getTabAt(position));
    notifyDataSetChanged();
}

解决方案与夏洛克动作栏和滑动手势。

2013-07-24 11:25:57

我做了一些类似于wize的事情，但在我的回答中，你可以随时在两个片段之间更改。在改变屏幕方向之类的时候，我遇到了一些问题。这是PagerAdapter的样子:

    public class MyAdapter extends FragmentPagerAdapter
{
    static final int NUM_ITEMS = 2;
    private final FragmentManager mFragmentManager;
    private Fragment mFragmentAtPos0;
     private Map<Integer, String> mFragmentTags;
     private boolean isNextFragment=false;

    public MyAdapter(FragmentManager fm)
    {
        super(fm);
        mFragmentManager = fm;
         mFragmentTags = new HashMap<Integer, String>();
    }

    @Override
    public Fragment getItem(int position)
    {
        if (position == 0)
        {


            if (isPager) {
                mFragmentAtPos0 = new FirstPageFragment();
            } else {
                mFragmentAtPos0 = new NextFragment();
            }
            return mFragmentAtPos0;
        }
        else
            return SecondPageFragment.newInstance();
    }

    @Override
    public int getCount()
    {
        return NUM_ITEMS;
    }


 @Override
    public Object instantiateItem(ViewGroup container, int position) {
        Object obj = super.instantiateItem(container, position);
        if (obj instanceof Fragment) {
            // record the fragment tag here.
            Fragment f = (Fragment) obj;
            String tag = f.getTag();
            mFragmentTags.put(position, tag);
        }
        return obj;
    }


    public void onChange(boolean isNextFragment) {

        if (mFragmentAtPos0 == null)
            mFragmentAtPos0 = getFragment(0);
        if (mFragmentAtPos0 != null)
            mFragmentManager.beginTransaction().remove(mFragmentAtPos0).commit();


        if (!isNextFragment) {
            mFragmentAtFlashcards = new FirstPageFragment();
        } else {
            mFragmentAtFlashcards = new NextFragment();
        }

        notifyDataSetChanged();


    }


    @Override
    public int getItemPosition(Object object)
    {
        if (object instanceof FirstPageFragment && mFragmentAtPos0 instanceof NextFragment)
            return POSITION_NONE;
         if (object instanceof NextFragment && mFragmentAtPos0 instanceof FirstPageFragment)
            return POSITION_NONE;
        return POSITION_UNCHANGED;
    }


    public Fragment getFragment(int position) {
        String tag = mFragmentTags.get(position);
        if (tag == null)
            return null;
        return mFragmentManager.findFragmentByTag(tag);
    }
}

我在适配器容器活动中实现的侦听器，用于在附加片段时将其放到片段中，这是活动:

    public class PagerContainerActivity extends AppCompatActivity implements ChangeFragmentListener {

//...

  @Override
    public void onChange(boolean isNextFragment) {
        if (pagerAdapter != null)
            pagerAdapter.onChange(isNextFragment);


    }

//...
}

然后在片段中放置侦听器，当附加调用它:

public class FirstPageFragment extends Fragment{


private ChangeFragmentListener changeFragmentListener;


//...
 @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        changeFragmentListener = ((PagerContainerActivity) activity);
    }

    @Override
    public void onDetach() {
        super.onDetach();
        changeFragmentListener = null;
    }
//...
//in the on click to change the fragment
changeFragmentListener.onChange(true);
//...
}

最后是听众:

public interface changeFragmentListener {

    void onChange(boolean isNextFragment);

}

2015-06-08 15:18:02

Here's my relatively simple solution to this problem. The keys to this solution are to use FragmentStatePagerAdapter instead of FragmentPagerAdapter as the former will remove unused fragments for you while the later still retains their instances. The second is the use of POSITION_NONE in getItem(). I've used a simple List to keep track of my fragments. My requirement was to replace the entire list of fragments at once with a new list, but the below could be easily modified to replace individual fragments:

public class MyFragmentAdapter extends FragmentStatePagerAdapter {
    private List<Fragment> fragmentList = new ArrayList<Fragment>();
    private List<String> tabTitleList = new ArrayList<String>();

    public MyFragmentAdapter(FragmentManager fm) {
        super(fm);
    }

    public void addFragments(List<Fragment> fragments, List<String> titles) {
        fragmentList.clear();
        tabTitleList.clear();
        fragmentList.addAll(fragments);
        tabTitleList.addAll(titles);
        notifyDataSetChanged();
    }

    @Override
    public int getItemPosition(Object object) {
        if (fragmentList.contains(object)) {
            return POSITION_UNCHANGED;
        }
        return POSITION_NONE;
    }

    @Override
    public Fragment getItem(int item) {
        if (item >= fragmentList.size()) {
            return null;
        }
        return fragmentList.get(item);
    }

    @Override
    public int getCount() {
        return fragmentList.size();
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return tabTitleList.get(position);
    }
}

2012-10-11 20:54:25

我按照@wize和@mdelolmo的答案，我得到了解决方案。由于吨。但是，我稍微调整了这些解决方案，以提高内存消耗。

我观察到的问题:

这是我的实现。

  public static class DemoCollectionPagerAdapter extends FragmentStatePagerAdapter {

    private SwitchFragListener mSwitchFragListener;
    private Switch mToggle;
    private int pagerAdapterPosChanged = POSITION_UNCHANGED;
    private static final int TOGGLE_ENABLE_POS = 2;


    public DemoCollectionPagerAdapter(FragmentManager fm, Switch toggle) {
        super(fm);
        mToggle = toggle;

        mSwitchFragListener = new SwitchFragListener();
        mToggle.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                mSwitchFragListener.onSwitchToNextFragment();
            }
        });
    }

    @Override
    public Fragment getItem(int i) {
        switch (i)
        {
            case TOGGLE_ENABLE_POS:
                if(mToggle.isChecked())
                {
                    return TabReplaceFragment.getInstance();
                }else
                {
                    return DemoTab2Fragment.getInstance(i);
                }

            default:
                return DemoTabFragment.getInstance(i);
        }
    }

    @Override
    public int getCount() {
        return 5;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return "Tab " + (position + 1);
    }

    @Override
    public int getItemPosition(Object object) {

        //  This check make sures getItem() is called only for the required Fragment
        if (object instanceof TabReplaceFragment
                ||  object instanceof DemoTab2Fragment)
            return pagerAdapterPosChanged;

        return POSITION_UNCHANGED;
    }

    /**
     * Switch fragments Interface implementation
     */
    private final class SwitchFragListener implements
            SwitchFragInterface {

        SwitchFragListener() {}

        public void onSwitchToNextFragment() {

            pagerAdapterPosChanged = POSITION_NONE;
            notifyDataSetChanged();
        }
    }

    /**
     * Interface to switch frags
     */
    private interface SwitchFragInterface{
        void onSwitchToNextFragment();
    }
}

演示链接在这里..https://youtu.be/l_62uhKkLyM

出于演示目的，在位置2处使用了两个片段TabReplaceFragment和DemoTab2Fragment。在所有其他情况下，我使用DemoTabFragment实例。

解释:

再次感谢@wize和@mdelolmo的原创想法。

希望这对你有帮助。：）

如果这个实现有任何缺陷，请告诉我。那将对我的项目大有帮助。

2016-06-22 05:16:54

我找到了一个简单的解决方案，即使你想在中间添加新的片段或替换当前片段，它也能很好地工作。在我的解决方案中，您应该重写getItemId()，它应该为每个片段返回唯一的id。不是默认的位置。

就是这样:

public class DynamicPagerAdapter extends FragmentPagerAdapter {

private ArrayList<Page> mPages = new ArrayList<Page>();
private ArrayList<Fragment> mFragments = new ArrayList<Fragment>();

public DynamicPagerAdapter(FragmentManager fm) {
    super(fm);
}

public void replacePage(int position, Page page) {
    mPages.set(position, page);
    notifyDataSetChanged();
}

public void setPages(ArrayList<Page> pages) {
    mPages = pages;
    notifyDataSetChanged();
}

@Override
public Fragment getItem(int position) {
    if (mPages.get(position).mPageType == PageType.FIRST) {
        return FirstFragment.newInstance(mPages.get(position));
    } else {
        return SecondFragment.newInstance(mPages.get(position));
    }
}

@Override
public int getCount() {
    return mPages.size();
}

@Override
public long getItemId(int position) {
    // return unique id
    return mPages.get(position).getId();
}

@Override
public Object instantiateItem(ViewGroup container, int position) {
    Fragment fragment = (Fragment) super.instantiateItem(container, position);
    while (mFragments.size() <= position) {
        mFragments.add(null);
    }
    mFragments.set(position, fragment);
    return fragment;
}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    super.destroyItem(container, position, object);
    mFragments.set(position, null);
}

@Override
public int getItemPosition(Object object) {
    PagerFragment pagerFragment = (PagerFragment) object;
    Page page = pagerFragment.getPage();
    int position = mFragments.indexOf(pagerFragment);
    if (page.equals(mPages.get(position))) {
        return POSITION_UNCHANGED;
    } else {
        return POSITION_NONE;
    }
}
}

注意:在这个例子中，FirstFragment和SecondFragment扩展了抽象类PageFragment，它有方法getPage()。

2014-04-22 11:39:01

在ViewPager中替换Fragment

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