问题
there is a MainActivity with it's fragment named FragmentOne. i have a List of items in this fragment and these data are save in my database
i make changes from NavigationView in MainActivity .. i try to delete all rows from my database. it works, but after that i need to refresh my FragmentOne, how can i refresh the FragmentOne UI ?
i have a method named updateUI in my FragmentOne but how could i access that method? when i make that method public everything just goes wrong!
i tested different ways but failed.. can anybody tell me how can i do this?
MainActivity :
public class MainActivity extends AppCompatActivity {
private DrawerLayout mDrawerLayout;
private TabLayout tabLayout;
private ViewPager viewPager;
private Detail mDetail;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//////// TOOLBAR
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
ActionBar actionBar = getSupportActionBar();
actionBar.setHomeAsUpIndicator(R.drawable.ic_menu);
actionBar.setDisplayHomeAsUpEnabled(true);
///////// DRAWER
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
NavigationView navigationView =
(NavigationView) findViewById(R.id.navigation_view);
navigationView.setNavigationItemSelectedListener
(new NavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(MenuItem menuItem) {
switch (menuItem.getItemId()) {
case R.id.nav_item_one:
return false;
case R.id.nav_item_two:
AlertDialog.Builder alert_delete = new AlertDialog.Builder(
MainActivity.this);
alert_delete.setTitle("Alert!");
alert_delete.setMessage(R.string.alert_delete_all);
alert_delete.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
DetailLab.get(getApplicationContext()).deleteAllDetail();
FragmentOne fragmentOne = new FragmentOne();
fragmentOne.getFragmentManager().beginTransaction().replace(R.id.card_view, fragmentOne)
.commit();
dialog.dismiss();
}
});
alert_delete.setNegativeButton("No", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
});
alert_delete.show();
return false;
..
..
case R.id.nav_item_nine:
finish();
default:
return false;
}
}
});
viewPager = (ViewPager) findViewById(R.id.viewpager);
setupViewPager(viewPager);
tabLayout = (TabLayout) findViewById(R.id.tablayout);
tabLayout.setupWithViewPager(viewPager);
setupTabIcons();
}
private void setupViewPager(ViewPager viewPager) {
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFragment(new FragmentOne(), "ONE");
adapter.addFragment(new FragmentTwo(), "TWO");
viewPager.setAdapter(adapter);
}
class ViewPagerAdapter extends FragmentPagerAdapter {
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public ViewPagerAdapter(FragmentManager manager) {
super(manager);
}
@Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}
@Override
public int getCount() {
return mFragmentList.size();
}
public void addFragment(Fragment fragment, String title) {
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
}
@Override
public CharSequence getPageTitle(int position) {
return null;
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
switch (id) {
case android.R.id.home:
mDrawerLayout.openDrawer(GravityCompat.START);
return true;
}
return super.onOptionsItemSelected(item);
}
}
here is my method for delete all rows from database in another class called DetailLab :
public void deleteAllDetail() {
mDatabase.delete(DetailTable.NAME, null, null); }
and this is my FragmentOne:
public class FragmentOne extends Fragment {
private static final String SAVED_NUMBER_VISIBLE = "number";
private RecyclerView mDetailRecyclerView;
private DetailAdapter mAdapter;
private boolean mNumberVisible;
private View view;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
view = inflater.inflate(R.layout.fragment_one_layout,
container, false);
mDetailRecyclerView = (RecyclerView)
view.findViewById(R.id.detail_recycler_view);
LinearLayoutManager layoutManager = new LinearLayoutManager(getContext());
layoutManager.setReverseLayout(true); //This will reverse the data order but not scroll the RecyclerView to the last item
layoutManager.setStackFromEnd(true); //For keeping data order same and simply scrolling the RecyclerView to the last item
mDetailRecyclerView.setLayoutManager(layoutManager);
if (savedInstanceState != null) {
mNumberVisible =
savedInstanceState.getBoolean(SAVED_NUMBER_VISIBLE);
}
updateUI();
return view;
}
@Override
public void onResume() {
super.onResume();
updateUI();
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putBoolean(SAVED_NUMBER_VISIBLE, mNumberVisible);
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
super.onCreateOptionsMenu(menu, inflater);
inflater.inflate(R.menu.fragment_one_layout, menu);
MenuItem numberItem = menu.findItem(R.id.show_numbers);
if (mNumberVisible) {
numberItem.setTitle(R.string.hide_numbers);
} else {
numberItem.setTitle(R.string.show_numbers);
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.show_numbers:
mNumberVisible = !mNumberVisible;
getActivity().invalidateOptionsMenu();
updateNumbers();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
private void updateNumbers() {
DetailLab detailLab = DetailLab.get(getActivity());
int detailCount = detailLab.getDetails().size();
String number = getResources().getQuantityString
(R.plurals.number_plural, detailCount, detailCount);
if (!mNumberVisible) {
number = null;
}
AppCompatActivity activity = (AppCompatActivity) getActivity();
activity.getSupportActionBar().setSubtitle(number);
}
private void updateUI() {
DetailLab detailLab = DetailLab.get(getActivity());
List<Detail> details = detailLab.getDetails();
if (details.size() == 0) {
TextView t = (TextView) view.findViewById(R.id.empty);
t.setText(R.string.empty_view);
t.setVisibility(View.VISIBLE);
} else {
TextView t = (TextView) view.findViewById(R.id.empty);
t.setVisibility(View.GONE);
}
// Toast.makeText(getContext(), "zero", Toast.LENGTH_SHORT).show();
if (mAdapter == null) {
mAdapter = new DetailAdapter(details);
mDetailRecyclerView.setAdapter(mAdapter);
} else {
mAdapter.setDetails(details);
mAdapter.notifyDataSetChanged();
}
updateNumbers();
}
private class DetailHolder extends RecyclerView.ViewHolder
implements View.OnClickListener, View.OnLongClickListener {
private TextView mTitleTextView;
// private TextView mDateTextView;
private Detail mDetail;
private RatingBar mRatingBar;
public DetailHolder(LayoutInflater inflater, ViewGroup parent) {
super(inflater.inflate(R.layout.list_item_detail,
parent, false));
itemView.setOnClickListener(this);
itemView.setOnLongClickListener(this);
mTitleTextView = (TextView) itemView.findViewById(R.id.detail_title);
// mDateTextView = (TextView) itemView.findViewById(R.id.detail_date);
mRatingBar = (RatingBar) itemView.findViewById(R.id.ratingBar);
}
public void bind(Detail detail) {
mDetail = detail;
mTitleTextView.setText(mDetail.getTitle());
mRatingBar.setRating(mDetail.getRate());
}
@Override
public void onClick(View view) {
Intent intent = DetailPagerActivity.newIntent(getActivity(),
mDetail.getId());
startActivity(intent);
}
@Override
public boolean onLongClick(View v) {
AlertDialog.Builder alert = new AlertDialog.Builder(
getActivity());
alert.setMessage(R.string.alert);
alert.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
DetailLab.get(getActivity()).deleteDetail(mDetail);
updateUI();
updateNumbers();
dialog.dismiss();
}
});
alert.setNegativeButton("No", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
});
alert.show();
return true;
}
}
private class DetailAdapter extends RecyclerView.Adapter<DetailHolder> {
private List<Detail> mDetails;
public DetailAdapter(List<Detail> details) {
mDetails = details;
}
@Override
public DetailHolder onCreateViewHolder(ViewGroup parent, int viewType) {
LayoutInflater layoutInflater =
LayoutInflater.from(getActivity());
return new DetailHolder(layoutInflater, parent);
}
@Override
public void onBindViewHolder(DetailHolder holder, int position) {
Detail detail = mDetails.get(position);
holder.bind(detail);
}
@Override
public int getItemCount() {
return mDetails.size();
}
public void setDetails(List<Detail> details) {
mDetails = details;
}
}
}
and here is my layout for FragmentOne :
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/fragment_one_layout">
<android.support.v7.widget.CardView
android:id="@+id/card_view"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<android.support.v7.widget.RecyclerView
android:id="@+id/detail_recycler_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
<TextView
android:id="@+id/empty"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="50dp"
android:textAlignment="center"
android:textSize="20sp"/>
</android.support.v7.widget.CardView>
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_marginRight="24dp"
android:layout_marginBottom="24dp"
android:src="@drawable/ic_menu_add"
android:scaleType="center"
app:elevation="8dp"
app:borderWidth="0dp"
/>
my logcat:
FATAL EXCEPTION: main
Process: com.drgnme.listhamrah, PID: 23454
java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.v4.app.FragmentTransaction android.support.v4.app.FragmentManager.beginTransaction()' on a null object reference
at com.drgnme.listhamrah.MainActivity$1$1.onClick(MainActivity.java:76)
at android.support.v7.app.AlertController$ButtonHandler.handleMessage(AlertController.java:161)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5451)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
回答1:
I think you are having this issue because of the below code in your MainActivity:
FragmentOne fragmentOne = new FragmentOne();
fragmentOne.getFragmentManager().beginTransaction().replace(R.id.card_view, fragmentOne).commit();
You try to get the instance of the fragment manager with getFragmentManager() who call Activity.getFragmentManager but your fragmentOne isn't attach to the activity so the method return null and you get a java.lang.NullPointerException
Instead of fragmentOne.getFragmentManager() use getSupportFragmentManager() directly from the activity.
Hope this helps.
回答2:
I have a method named updateUI in my FragmentOne but how could i access that method?
To call the updateUI method of your FragmentOne
alert_delete.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
DetailLab.get(getApplicationContext()).deleteAllDetail();
Fragment page = getSupportFragmentManager().findFragmentByTag("android:switcher:" + R.id.pager + ":" + ViewPager.getCurrentItem());
// based on the current position you can then cast the page to the correct
// class and call the method:
if (ViewPager.getCurrentItem() == 0 && page != null) {
((FragmentOne)page).updateUI();
}
dialog.dismiss();
}
});
回答3:
To refresh a fragment's UI, use the fragment manager to detach and attach the same fragment again.
Eg:
public void refreshFragmentUI(Fragment fragment) {
getSupportFragmentManager()
.beginTransaction()
.detach(fragment)
.attach(fragment)
.commit();
}
Note: Use getSupportFragmentManager() if you are using support libraries. Else use getFragmentManager()
回答4:
The best way to update data from SQLite Database in fragment is using LoaderManager.LoaderCallbacks and CursorAdapter. Because it is an Asynchronous process.
来源：https://stackoverflow.com/questions/45779596/refresh-fragment-after-changing-data-in-database