Question

我正在尝试将一些名称加载到列表中，但我似乎并没有走得太远。每当我尝试运行我的代码时，它就会给我这个：

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.gijbelssiemen.herexamen.Model.Artist.getNaam()' on a null object reference
                                                                           at com.gijbelssiemen.herexamen.TabFragment1.addArtistsToList(TabFragment1.java:97)
                                                                           at com.gijbelssiemen.herexamen.TabFragment1.onViewCreated(TabFragment1.java:66)

我的代码如下所示：

import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;
import android.widget.AdapterView;

import com.gijbelssiemen.herexamen.ArtistInfoActivity;
import com.gijbelssiemen.herexamen.Adapter.ArtistListAdapter;
import com.gijbelssiemen.herexamen.Database.DatabaseHelper;
import com.gijbelssiemen.herexamen.Model.Artist;

import java.util.ArrayList;


public class TabFragment1 extends Fragment {

View rootView;
DatabaseHelper db;
Artist artist;

Integer[] imageId = {
        R.drawable.asa_moto,
        R.drawable.bea1991,
        R.drawable.easter,
        R.drawable.he4rtbroken,
        R.drawable.kablam,
        R.drawable.le1f,
        R.drawable.pruikduif,
        R.drawable.sheniqua,
        R.drawable.syracuse
};

ArrayList<String> artists;

ListView listView;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    db = new DatabaseHelper(getActivity());
    artist = new Artist();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    rootView = inflater.inflate(R.layout.tab_fragment_1, container, false);
    db.deleteArtist(artist);
    addArtists();
    return rootView;
}

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    addArtistsToList();
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            long ids = parent.getItemIdAtPosition(position);
            int artistId = (int) ids;
            Log.d("ID", Long.toString(ids));
            Intent artistInfo = new Intent(getActivity(), ArtistInfoActivity.class);
            artistInfo.putExtra("Naam", db.getArtist(artistId + 1).getNaam());
            artistInfo.putExtra("Beschrijving", db.getArtist(artistId + 1).getBeschrijving());
            artistInfo.putExtra("Image", db.getArtist(artistId + 1).getImage());
            startActivity(artistInfo);
        }
    });
}

private void addArtists() {
    Log.d("Insert: ", "Inserting ..");
    db.addArtist(new Artist("ASA MOTO", R.string.asa_moto_description, R.drawable.asa_moto));
    db.addArtist(new Artist("BEA1991", R.string.bea1991_description, R.drawable.bea1991));
    db.addArtist(new Artist("EASTER", R.string.easter_description, R.drawable.easter));
    db.addArtist(new Artist("HE4RTBROKEN", R.string.he4rtbroken_description, R.drawable.he4rtbroken));
    db.addArtist(new Artist("KABLAM", R.string.kablam_description, R.drawable.kablam));
    db.addArtist(new Artist("LE1F", R.string.le1f_description, R.drawable.le1f));
    db.addArtist(new Artist("PRUIKDUIF", R.string.pruikduif_description, R.drawable.pruikduif));
    db.addArtist(new Artist("SHENIQUA WORLD TOUR", R.string.sheniqua_world_tour_description, R.drawable.sheniqua));
    db.addArtist(new Artist("SYRACUSE", R.string.syracuse_description, R.drawable.syracuse));
}

private void addArtistsToList() {
    artists = new ArrayList<String>();
    artists.add(db.getArtist(1).getNaam());
    artists.add(db.getArtist(2).getNaam());
    artists.add(db.getArtist(3).getNaam());
    artists.add(db.getArtist(4).getNaam());
    artists.add(db.getArtist(5).getNaam());
    artists.add(db.getArtist(6).getNaam());
    artists.add(db.getArtist(7).getNaam());
    artists.add(db.getArtist(8).getNaam());
    artists.add(db.getArtist(9).getNaam());

    ArtistListAdapter adapter = new ArtistListAdapter(getActivity(), artists, imageId);
    listView = (ListView) rootView.findViewById(R.id.list_view);
    listView.setAdapter(adapter);
}
}

如果有人能指出我正确的方向，那将是值得赞赏的。提前谢谢！

错误第97行：

artists.add(db.getArtist(1).getNaam());

和错误第66行：

addArtistsToList();

这是DatabaseHelper.java中的getArtist方法：

public Artist getArtist(int artistId) {
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.query(DatabaseContract.ArtistEntry.TABLE_NAME, new String[]{DatabaseContract.ArtistEntry._ID,
                    DatabaseContract.ArtistEntry.COLUMN_ARTIST_NAAM, DatabaseContract.ArtistEntry.COLUMN_BESCHRIJVING, DatabaseContract.ArtistEntry.COLUMN_IMAGE}, DatabaseContract.ArtistEntry._ID + "=?",
            new String[]{String.valueOf(artistId)}, null, null, null, null);
    if (cursor != null && cursor.moveToFirst()) {
        artist = new Artist(Integer.parseInt(cursor.getString(0)),
                cursor.getString(1), Integer.parseInt(cursor.getString(2)), Integer.parseInt(cursor.getString(3)));
    }

    return artist;
}

Answer 1

问题是db.getArtist（1）为null。您需要查看数据库并确保数据存在。设置断点并调试代码。

看起来您的代码是在创建视图时创建艺术家。你确定他们正在把它一直带到数据库吗？

NullPointerException我无法摆脱

1 个答案: