更改数据库中的数据后刷新片段

问题描述

限时删除！！

有一个MainActivity，它的片段名为FragmentOne.我在此片段中有一个项目列表，这些数据保存在我的数据库中

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

我在MainActivity中的NavigationView中进行了更改..我尝试从数据库中删除所有行.它可以正常工作，但是在那之后我需要刷新FragmentOne，该如何刷新FragmentOne UI?

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 ?

我的FragmentOne中有一个名为updateUI的方法，但是如何访问该方法?当我将该方法设为 public 时，一切都出错了！

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!

我测试了不同的方法，但是失败了.有人可以告诉我我该怎么做吗?

i tested different ways but failed.. can anybody tell me how can i do this?

MainActivity :

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);
}

}

这是我从另一个名为 DetailLab 的类中从数据库中删除所有行的方法:

here is my method for delete all rows from database in another class called DetailLab :

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

这是我的 FragmentOne :

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;
        }
    }
}

这是FragmentOne的布局:

<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"
    />

我的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)

推荐答案

由于MainActivity中的以下代码，我认为您遇到了这个问题:

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();

您尝试使用getFragmentManager()获取片段管理器的实例，该实例调用Activity.getFragmentManager，但您的fragmentOne未附加到活动，因此该方法返回null并得到一个java.lang.NullPointerException

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

直接从活动中使用getSupportFragmentManager()代替fragmentOne.getFragmentManager().

Instead of fragmentOne.getFragmentManager() use getSupportFragmentManager() directly from the activity.

希望这会有所帮助.

这篇关于更改数据库中的数据后刷新片段的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！

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