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。
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。
Works Great with AndroidTeam's solution, however I found that I needed the ability to go back much like FrgmentTransaction.addToBackStack(null) But merely adding this will only cause the Fragment to be replaced without notifying the ViewPager. Combining the provided solution with this minor enhancement will allow you to return to the previous state by merely overriding the activity's onBackPressed() method. The biggest drawback is that it will only go back one at a time which may result in multiple back clicks
private ArrayList<Fragment> bFragments = new ArrayList<Fragment>();
private ArrayList<Integer> bPosition = new ArrayList<Integer>();
public void replaceFragmentsWithBackOut(ViewPager container, Fragment oldFragment, Fragment newFragment) {
startUpdate(container);
// remove old fragment
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
int position = getFragmentPosition(oldFragment);
while (mSavedState.size() <= position) {
mSavedState.add(null);
}
//Add Fragment to Back List
bFragments.add(oldFragment);
//Add Pager Position to Back List
bPosition.add(position);
mSavedState.set(position, null);
mFragments.set(position, null);
mCurTransaction.remove(oldFragment);
// add new fragment
while (mFragments.size() <= position) {
mFragments.add(null);
}
mFragments.set(position, newFragment);
mCurTransaction.add(container.getId(), newFragment);
finishUpdate(container);
// ensure getItem returns newFragemtn after calling handleGetItemInbalidated()
handleGetItemInvalidated(container, oldFragment, newFragment);
container.notifyItemChanged(oldFragment, newFragment);
}
public boolean popBackImmediate(ViewPager container){
int bFragSize = bFragments.size();
int bPosSize = bPosition.size();
if(bFragSize>0 && bPosSize>0){
if(bFragSize==bPosSize){
int last = bFragSize-1;
int position = bPosition.get(last);
//Returns Fragment Currently at this position
Fragment replacedFragment = mFragments.get(position);
Fragment originalFragment = bFragments.get(last);
this.replaceFragments(container, replacedFragment, originalFragment);
bPosition.remove(last);
bFragments.remove(last);
return true;
}
}
return false;
}
希望这能帮助到一些人。
同样,就getFragmentPosition()而言,它几乎是反向的getItem()。你知道哪些片段去哪里,只是确保你返回正确的位置它将在。这里有一个例子:
@Override
protected int getFragmentPosition(Fragment fragment) {
if(fragment.equals(originalFragment1)){
return 0;
}
if(fragment.equals(replacementFragment1)){
return 0;
}
if(fragment.equals(Fragment2)){
return 1;
}
return -1;
}
要替换ViewPager中的片段,你可以将ViewPager、PagerAdapter和FragmentStatePagerAdapter类的源代码移动到你的项目中,并添加以下代码。
分为:viewpage:
public void notifyItemChanged(Object oldItem, Object newItem) {
if (mItems != null) {
for (ItemInfo itemInfo : mItems) {
if (itemInfo.object.equals(oldItem)) {
itemInfo.object = newItem;
}
}
}
invalidate();
}
FragmentStatePagerAdapter:
public void replaceFragmetns(ViewPager container, Fragment oldFragment, Fragment newFragment) {
startUpdate(container);
// remove old fragment
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
int position = getFragmentPosition(oldFragment);
while (mSavedState.size() <= position) {
mSavedState.add(null);
}
mSavedState.set(position, null);
mFragments.set(position, null);
mCurTransaction.remove(oldFragment);
// add new fragment
while (mFragments.size() <= position) {
mFragments.add(null);
}
mFragments.set(position, newFragment);
mCurTransaction.add(container.getId(), newFragment);
finishUpdate(container);
// ensure getItem returns newFragemtn after calling handleGetItemInbalidated()
handleGetItemInbalidated(container, oldFragment, newFragment);
container.notifyItemChanged(oldFragment, newFragment);
}
protected abstract void handleGetItemInbalidated(View container, Fragment oldFragment, Fragment newFragment);
protected abstract int getFragmentPosition(Fragment fragment);
handleGetItemInvalidated()确保下一次调用getItem()后返回newFragment
getFragmentPosition()返回片段在适配器中的位置。
现在,替换片段调用
mAdapter.replaceFragmetns(mViewPager, oldFragment, newFragment);
如果你对一个示例项目感兴趣,请向我索取资源。
一些提出的解决方案帮助我很多,部分解决问题,但仍有一个重要的事情,在解决方案中产生了意想不到的异常和黑页内容,而不是在某些情况下的片段内容。
问题是FragmentPagerAdapter类使用条目ID将缓存的片段存储到FragmentManager中。出于这个原因,您还需要重写getItemId(int position)方法,以便它返回例如顶级页面的位置和详细页面的100 +位置。否则,之前创建的顶级片段将从缓存返回,而不是细节级片段。
Furthermore, I'm sharing here a complete example how to implement tabs-like activity with Fragment pages using ViewPager and tab buttons using RadioGroup that allows replacement of top-level pages with detailed pages and also supports back button. This implementation supports only one level of back stacking (item list - item details) but multi-level back stacking implementation is straightforward. This example works pretty well in normal cases except of it is throwing a NullPointerException in case when you switch to e. g. second page, change the fragment of the first page (while not visible) and return back to the first page. I'll post a solution to this issue once I'll figure it out:
public class TabsActivity extends FragmentActivity {
public static final int PAGE_COUNT = 3;
public static final int FIRST_PAGE = 0;
public static final int SECOND_PAGE = 1;
public static final int THIRD_PAGE = 2;
/**
* Opens a new inferior page at specified tab position and adds the current page into back
* stack.
*/
public void startPage(int position, Fragment content) {
// Replace page adapter fragment at position.
mPagerAdapter.start(position, content);
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Initialize basic layout.
this.setContentView(R.layout.tabs_activity);
// Add tab fragments to view pager.
{
// Create fragments adapter.
mPagerAdapter = new PagerAdapter(pager);
ViewPager pager = (ViewPager) super.findViewById(R.id.tabs_view_pager);
pager.setAdapter(mPagerAdapter);
// Update active tab in tab bar when page changes.
pager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageScrolled(int index, float value, int nextIndex) {
// Not used.
}
@Override
public void onPageSelected(int index) {
RadioGroup tabs_radio_group = (RadioGroup) TabsActivity.this.findViewById(
R.id.tabs_radio_group);
switch (index) {
case 0: {
tabs_radio_group.check(R.id.first_radio_button);
}
break;
case 1: {
tabs_radio_group.check(R.id.second_radio_button);
}
break;
case 2: {
tabs_radio_group.check(R.id.third_radio_button);
}
break;
}
}
@Override
public void onPageScrollStateChanged(int index) {
// Not used.
}
});
}
// Set "tabs" radio group on checked change listener that changes the displayed page.
RadioGroup radio_group = (RadioGroup) this.findViewById(R.id.tabs_radio_group);
radio_group.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(RadioGroup radioGroup, int id) {
// Get view pager representing tabs.
ViewPager view_pager = (ViewPager) TabsActivity.this.findViewById(R.id.tabs_view_pager);
if (view_pager == null) {
return;
}
// Change the active page.
switch (id) {
case R.id.first_radio_button: {
view_pager.setCurrentItem(FIRST_PAGE);
}
break;
case R.id.second_radio_button: {
view_pager.setCurrentItem(SECOND_PAGE);
}
break;
case R.id.third_radio_button: {
view_pager.setCurrentItem(THIRD_PAGE);
}
break;
}
});
}
}
@Override
public void onBackPressed() {
if (!mPagerAdapter.back()) {
super.onBackPressed();
}
}
/**
* Serves the fragments when paging.
*/
private class PagerAdapter extends FragmentPagerAdapter {
public PagerAdapter(ViewPager container) {
super(TabsActivity.this.getSupportFragmentManager());
mContainer = container;
mFragmentManager = TabsActivity.this.getSupportFragmentManager();
// Prepare "empty" list of fragments.
mFragments = new ArrayList<Fragment>(){};
mBackFragments = new ArrayList<Fragment>(){};
for (int i = 0; i < PAGE_COUNT; i++) {
mFragments.add(null);
mBackFragments.add(null);
}
}
/**
* Replaces the view pager fragment at specified position.
*/
public void replace(int position, Fragment fragment) {
// Get currently active fragment.
Fragment old_fragment = mFragments.get(position);
if (old_fragment == null) {
return;
}
// Replace the fragment using transaction and in underlaying array list.
// NOTE .addToBackStack(null) doesn't work
this.startUpdate(mContainer);
mFragmentManager.beginTransaction().setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
.remove(old_fragment).add(mContainer.getId(), fragment)
.commit();
mFragments.set(position, fragment);
this.notifyDataSetChanged();
this.finishUpdate(mContainer);
}
/**
* Replaces the fragment at specified position and stores the current fragment to back stack
* so it can be restored by #back().
*/
public void start(int position, Fragment fragment) {
// Remember current fragment.
mBackFragments.set(position, mFragments.get(position));
// Replace the displayed fragment.
this.replace(position, fragment);
}
/**
* Replaces the current fragment by fragment stored in back stack. Does nothing and returns
* false if no fragment is back-stacked.
*/
public boolean back() {
int position = mContainer.getCurrentItem();
Fragment fragment = mBackFragments.get(position);
if (fragment == null) {
// Nothing to go back.
return false;
}
// Restore the remembered fragment and remove it from back fragments.
this.replace(position, fragment);
mBackFragments.set(position, null);
return true;
}
/**
* Returns fragment of a page at specified position.
*/
@Override
public Fragment getItem(int position) {
// If fragment not yet initialized, create its instance.
if (mFragments.get(position) == null) {
switch (position) {
case FIRST_PAGE: {
mFragments.set(FIRST_PAGE, new DefaultFirstFragment());
}
break;
case SECOND_PAGE: {
mFragments.set(SECOND_PAGE, new DefaultSecondFragment());
}
break;
case THIRD_PAGE: {
mFragments.set(THIRD_PAGE, new DefaultThirdFragment());
}
break;
}
}
// Return fragment instance at requested position.
return mFragments.get(position);
}
/**
* Custom item ID resolution. Needed for proper page fragment caching.
* @see FragmentPagerAdapter#getItemId(int).
*/
@Override
public long getItemId(int position) {
// Fragments from second level page hierarchy have their ID raised above 100. This is
// important to FragmentPagerAdapter because it is caching fragments to FragmentManager with
// this item ID key.
Fragment item = mFragments.get(position);
if (item != null) {
if ((item instanceof NewFirstFragment) || (item instanceof NewSecondFragment) ||
(item instanceof NewThirdFragment)) {
return 100 + position;
}
}
return position;
}
/**
* Returns number of pages.
*/
@Override
public int getCount() {
return mFragments.size();
}
@Override
public int getItemPosition(Object object)
{
int position = POSITION_UNCHANGED;
if ((object instanceof DefaultFirstFragment) || (object instanceof NewFirstFragment)) {
if (object.getClass() != mFragments.get(FIRST_PAGE).getClass()) {
position = POSITION_NONE;
}
}
if ((object instanceof DefaultSecondragment) || (object instanceof NewSecondFragment)) {
if (object.getClass() != mFragments.get(SECOND_PAGE).getClass()) {
position = POSITION_NONE;
}
}
if ((object instanceof DefaultThirdFragment) || (object instanceof NewThirdFragment)) {
if (object.getClass() != mFragments.get(THIRD_PAGE).getClass()) {
position = POSITION_NONE;
}
}
return position;
}
private ViewPager mContainer;
private FragmentManager mFragmentManager;
/**
* List of page fragments.
*/
private List<Fragment> mFragments;
/**
* List of page fragments to return to in onBack();
*/
private List<Fragment> mBackFragments;
}
/**
* Tab fragments adapter.
*/
private PagerAdapter mPagerAdapter;
}
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()。