我进行了一个选项卡式视图活动，其中有两个选项卡，当然还有两个片段。 我需要为每个片段设置标签，因为我想向它们发送数据，并且应该知道它们是否已创建（according to Deliver a message to Fragment）
但是我有一个问题。目前，我在getItem方法中创建了片段的新实例并为其设置了Tag，以便在另一个位置（getCurrencies方法）检测该片段以向其发送数据。但是在getItem中，我必须创建我的片段的另一个实例并返回它，这就是问题所在！ 我必须创建两个片段实例！请查看下面的代码，您将会发现。
public class DashboardActivity extends AppCompatActivity {
private SectionsPagerAdapter mSectionsPagerAdapter;
private ViewPager mViewPager;
List < CurrencyModel > currencies;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_dashboard);
getCurrencies();
setSupportActionBar(toolbar);
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
mViewPager = (ViewPager) findViewById(R.id.container);
mViewPager.setAdapter(mSectionsPagerAdapter);
TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
mViewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.addOnTabSelectedListener(new TabLayout.ViewPagerOnTabSelectedListener(mViewPager));
}
public void getCurrencies() {
APIInterface apiInterface = APIClient.getClient().create(APIInterface.class);
Call < GetCurrenciesModel > call = apiInterface.getCurrencies();
call.enqueue(new Callback < GetCurrenciesModel > () {
@Override
public void onResponse(Call < GetCurrenciesModel > call, Response < GetCurrenciesModel > response) {
if (response.isSuccessful()) {
if (response.body().getStatus() == true) {
currencies = new ArrayList < CurrencyModel > ();
for (int i = 0; i < response.body().getCurrencies().size(); i++) {
currencies.add(response.body().getCurrencies().get(i));
}
FeesFragment fragment = (FeesFragment) getSupportFragmentManager().findFragmentByTag("FEESFRAGMENT");
if (fragment != null) {
fragment.caller(currencies);
} else {
FeesFragment feesFragment = new FeesFragment();
Bundle bundle = new Bundle();
bundle.putParcelableArrayList("Curren", (ArrayList << ? extends Parcelable > ) currencies);
feesFragment.setArguments(bundle);
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.fees_fragment_view, feesFragment);
transaction.addToBackStack(null);
// Commit the transaction
transaction.commit();
}
}
}
}
@Override
public void onFailure(Call < GetCurrenciesModel > call, Throwable t) {
}
});
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
public PlaceholderFragment() {}
/**
* Returns a new instance of this fragment for the given section
* number.
*/
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
}
/**
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to
* one of the sections/tabs/pages.
*/
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return new ExchangeFragment();
case 1:
Fragment feesFragment = new FeesFragment();
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fees_fragment_view, feesFragment, "FEESFRAGMENT");
fragmentTransaction.commit();
return new FeesFragment();
}
return null;
}
@Override
public int getCount() {
// Show 3 total pages.
return 2;
}
}
}
答案 0 :(得分：0)
在创建新实例之前，我正在检查FragmentManager中的片段实例。当PagerAdapter需要它们时，我会标记每个片段实例，并在实例化新实例之前在FragmentManager中搜索现有实例。这是我正在使用的代码。
PagerAdapter类：
private class PagerAdapter extends FragmentPagerAdapter {
private static final int PAGE_COUNT = 3;
private FragmentManager fragmentManager;
private PagerAdapter(FragmentManager fragmentManager) {
super(fragmentManager);
this.fragmentManager = fragmentManager;
}
@Override
public Fragment getItem(int position) {
Fragment fragment = fragmentManager.findFragmentByTag("android:switcher:" +
viewPager.getId() + ":" + getItemId(position));
if (fragment != null) {
return fragment;
} else {
switch (position) {
case 0:
return FinderOrganizationsFragment.newInstance();
case 1:
return FinderUsersFragment.newInstance();
case 2:
return FinderBusinessesFragment.newInstance();
default:
return null;
}
}
}
@Override
public int getCount() {
return PAGE_COUNT;
}
}
newInstance方法：
public static FinderOrganizationsFragment newInstance() {
return new FinderOrganizationsFragment();
}