在更改数据库中的数据后刷新片段

Question

有一个MainActivity与它的片段命名为FragmentOne。我有这个片段中的项目列表，这些数据保存在我的数据库中

我从NavigationView在MainActivity ..我尝试从我的数据库中删除所有行。它的工作原理，但之后，我需要刷新我的FragmentOne，我怎么刷新FragmentOne用户界面？

我在我的FragmentOne中有一个名为updateUI的方法，但我如何访问该方法？当我做出这种方法公众一切都出错了！

我测试过不同的方式，但失败..有人可以告诉我我怎么能做到这一点？

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); 
} 

} 

这里是我删除另一个叫DetailLab类从数据库中的所有行的方法：

public void deleteAllDetail() { 
     mDatabase.delete(DetailTable.NAME, null, null); } 

，这是我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; 
     } 
    } 
} 

，这里是我的FragmentOne布局：

<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" 
    /> 

我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) 

Answer 1

我以为你是因为下面的代码在您的MainActivity这个问题：

FragmentOne fragmentOne = new FragmentOne(); 
fragmentOne.getFragmentManager().beginTransaction().replace(R.id.card_view, fragmentOne).commit(); 

你尝试用getFragmentManager()谁打电话Activity.getFragmentManager但你fragmentOne得到片段管理器实例不附加到活动，所以方法返回null，你会得到一个java.lang.NullPointerException

而不是fragmentOne.getFragmentManager()使用getSupportFragmentManager()直接从活动。

希望这会有所帮助。

Answer 2

要刷新一个片段的UI，使用碎片经理分离和附加相同再次碎片。

如：

public void refreshFragmentUI(Fragment fragment) { 
     getSupportFragmentManager() 
      .beginTransaction() 
      .detach(fragment) 
      .attach(fragment) 
      .commit(); 
    } 

注意：使用getSupportFragmentManager()如果您使用支持库。否则，使用getFragmentManager()

Answer 3

我有一个在我的FragmentOne命名updateUI方法，但我怎么能 访问方法？

调用您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(); 
          } 
         }); 

Answer 4

更新从片段SQLite数据库数据的最佳方式updateUI方法是使用LoaderManager.LoaderCallbacks和CursorAdapter的。因为它是一个异步进程。