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我的应用在肖像模式下使用ViewPager，在横向模式下使用双片段布局。从活动中调用片段时调用方法的菜单项为空
我试图启动AsyncTask，即在Fragment，从Activity。 AsyncTask通常从Actionbar中的菜单项开始，但我需要从Activity以编程方式启动它。
菜单项是ImageView，我正在为AsyncTask运行时为其制作动画。我的代码在双片段横向视图中工作正常，但在纵向模式下，我在菜单项上获得NullPointerException。
活动
public class Main extends SherlockFragmentActivity
{
private static List<Integer> mIds;
private static SparseArray<Fragment> mPageReferenceMap = new SparseArray<Fragment>();
@Override
public void onCreate(final Bundle icicle)
{
super.onCreate(icicle);
setContentView(R.layout.main);
mViewPager = (ViewPager)findViewById(R.id.viewpager); //view pager exists, so we are using the portait layout
if (mViewPager != null)
{
mIds = new ArrayList<Integer>();
mIds.add(0);
mIds.add(1);
mIds.add(2);
}
else //in landscape
{
ListFragment lf = (ListFragment)getSupportFragmentManager().findFragmentById(R.id.fragmentList);
if (lf == null)
lf = new ListFragment();
DetailFragment df = (DetailFragment)getSupportFragmentManager().findFragmentById(R.id.fragmentDetail);
if (df == null)
{
df = new DetailFragment();
df.setArguments(getIntent().getExtras());
}
getSupportFragmentManager().beginTransaction().add(R.id.fragmentList, lf).commit();
getSupportFragmentManager().beginTransaction().add(R.id.fragmentDetail, df).commit();
}
final MyFragmentPagerAdapter fpa = (MyFragmentPagerAdapter)mViewPager.getAdapter();
ListFragment lf2 = (ListFragment)fpa.getFragment(0);
//this works if I use:
//(ListFragment)getSupportFragmentManager().findFragmentById(R.id.fragmentList);
lf2.RunTask();
}
private static class MyFragmentPagerAdapter extends FragmentStatePagerAdapter {
public MyFragmentPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int index) {
if (index == 0)
{
ListFragment lf = ListFragment.newInstance();
mPageReferenceMap.put(index, lf);
return lf;
}
else
{
DetailFragment df = DetailFragment.newInstance(mIds.get(index-1));
mPageReferenceMap.put(index, df);
return df;
}
public Fragment getFragment(int key) {
return mPageReferenceMap.get(key);
}
public void destroyItem(View container, int position, Object object) {
super.destroyItem(container, position, object);
mPageReferenceMap.remove(position);
}
@Override
public int getCount() {
return 4;
}
}
}
片段
public class ListingFragment extends SherlockListFragment
{
private MenuItem refreshItem;
public static ListingFragment newInstance() {
ListingFragment lf = new ListingFragment();
return lf;
}
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.listing_layout, container, false);
}
private void StartAnimation() {
final LayoutInflater inflater = (LayoutInflater)getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
final ImageView ivRefresh = (ImageView)inflater.inflate(R.layout.refresh_view, null);
final Animation rotation = AnimationUtils.loadAnimation(getActivity(), R.anim.refresh);
ivRefresh.startAnimation(rotation);
//this is null
refreshItem.setActionView(ivRefresh);
}
public void StopAnimation()
{
if (refreshItem != null && refreshItem.getActionView() != null)
{
refreshItem.getActionView().clearAnimation();
refreshItem.setActionView(null);
}
}
public void RunTask()
{
new GetItems().execute();
}
private class GetItems extends AsyncTask<Void, Void, Void>
{
@Override
protected void onPreExecute()
{
StartAnimation();
}
@Override
protected Void doInBackground(Void... unused)
{
...
}
protected void onPostExecute(final Void unused)
{
StopAnimation();
}
}
@Override
public void onCreateOptionsMenu(final Menu menu, final MenuInflater inflater) {
inflater.inflate(R.menu.keyword_menu, menu);
refreshItem = menu.findItem(R.id.get);
super.onCreateOptionsMenu(menu, inflater);
}
@Override
public boolean onOptionsItemSelected(final MenuItem item)
{
if (item.getItemId() == R.id.get) {
gi = new GetItems(getActivity(), null);
gi.execute();
return true;
} else {
return super.onOptionsItemSelected(item);
}
}
}