具有 ListView 可见性的 SimpleCursorAdapter

Question

您好，我创建了一个数据库，我试图在列表视图中列出该数据库的名称，但没有显示任何内容。

mty 数据库的代码是：

public class LockedInDatabaseHelper extends SQLiteOpenHelper {

    private static final String DB_NAME = "Locked In";
    private static final int DB_VERSION = 1;

    public LockedInDatabaseHelper(Context context) {

        super(context, DB_NAME, null, DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE ARTISTS (_id INTEGER PRIMARY KEY AUTOINCREMENT,"
                    + "NAME TEXT,"
                    + "INTRO TEXT,"
                    +"IMAGE_RESCOURCE_ID INT)");
        insertArtist(db, "Jinx Inkz", "An artist who specializes in portraits and custom pieces", R.drawable.jinx_profile);
        insertArtist(db, "Bazooka Zook", "An artist who specializes in clean line work and neo - traditional", R.drawable.zook_profile );

            }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    private static void insertArtist(SQLiteDatabase db, String name, String intro, int resourceId){
        ContentValues artistInfo = new ContentValues();
        artistInfo.put("NAME", name);
        artistInfo.put("INTRO", intro);
        artistInfo.put("IMAGE_RESOURCE_ID", resourceId);
        db.insert("ARTISTS",null, artistInfo);
    }

}

最后，我希望信息出现的地方的 java 代码是

public class ArtistsActivity extends AppCompatActivity {

private SQLiteDatabase db;
private Cursor cursor;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_artists);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    ListView listArtists = (ListView) findViewById(R.id.artistsLV);
    SQLiteOpenHelper lockedInDatabaseHelper = new LockedInDatabaseHelper(ArtistsActivity.this);
    try {
        db = lockedInDatabaseHelper.getReadableDatabase();
        cursor = db.query("ARTISTS",
                new String[]{"_id", "NAME"},
                null, null, null, null, null);
        SimpleCursorAdapter listAdapter = new SimpleCursorAdapter(ArtistsActivity.this,
                android.R.layout.simple_list_item_1,
                cursor,
                new String[]{"NAME"},
                new int[] {android.R.id.text1},
                0);
        listArtists.setAdapter(listAdapter);
    } catch (SQLiteException e) {

        Toast toast = Toast.makeText(this, "Database unavailable", Toast.LENGTH_LONG);
        toast.show();

    }

    //Create a listener for clicks on listview
    AdapterView.OnItemClickListener itemClickListener =
            new AdapterView.OnItemClickListener() {
        public void onItemClick(AdapterView<?> listArtists,
                                View itemView,
                                int position,
                                long id){
            //Pass tha artist user clicks on to artistActivity
            Intent intent = new Intent(ArtistsActivity.this, ArtistDetail.class);
            intent.putExtra(ArtistDetail.EXTRA_ARTISTID, (int) id);
            startActivity(intent);

        }
    };
    //Assign the listener to list view
    listArtists.setOnItemClickListener(itemClickListener);
    }

    @Override
    public void onDestroy(){
    super.onDestroy();
    cursor.close();
    db.close();
    }
}

我一直在研究代码，但我认为它与 ListView 无关。请帮忙！我超级卡住了，我只想要一个列表，我可以添加一个 onClickListener 以继续应用程序。

Answer 1

您的问题是列名 IMAGE_RESOURCE_ID 拼写错误。也就是说，您使用列名 IMAGE_RESCOURCE_ID 创建表，但尝试插入列 IMAGE_RESOURCE_ID。

我建议始终对表名和列名使用常量，因此您只需定义一次，然后使用相同的常量来引用这些项目。

因此，我建议将数据库助手 LockedInDatabaseHelper.java 更改为 :-

public class LockedInDatabaseHelper extends SQLiteOpenHelper {

    private static final String DB_NAME = "Locked In";
    private static final int DB_VERSION = 1;
    public static final String TBL_ARTISTS = "ARTISTS";
    public static final String COL_ID = BaseColumns._ID;
    public static final String COl_NAME = "NAME";
    public static final String COL_INTRO = "INTRO";
    public static final String COL_IMAGERESOURCEID = "IMAGE_RESOURCE_ID";

    public LockedInDatabaseHelper(Context context) {

        super(context, DB_NAME, null, DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE ARTISTS (" + COL_ID + " INTEGER PRIMARY KEY,"
                + COl_NAME + " TEXT,"
                + COL_INTRO + " TEXT,"
                + COL_IMAGERESOURCEID + " INT)");
        insertArtist(db, "Jinx Inkz", "An artist who specializes in portraits and custom pieces", R.drawable.jinx_profile);
        insertArtist(db, "Bazooka Zook", "An artist who specializes in clean line work and neo - traditional",R.drawable.zook_profile);

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    private static void insertArtist(SQLiteDatabase db, String name, String intro, int resourceId){
        ContentValues artistInfo = new ContentValues();
        artistInfo.put(COl_NAME, name);
        artistInfo.put(COL_INTRO, intro);
        artistInfo.put(COL_IMAGERESOURCEID, resourceId);
        db.insert(TBL_ARTISTS,null, artistInfo);
    }
}

除了对 ArtistsActivity.java 进行了一些更改，还可以利用常量，以便它包含：-

cursor = db.query(LockedInDatabaseHelper.TBL_ARTISTS,
                    new String[]{LockedInDatabaseHelper.COL_ID, "NAME"},
                    null, null, null, null, null);
            SimpleCursorAdapter listAdapter = new SimpleCursorAdapter(ArtistsActivity.this,
                    android.R.layout.simple_list_item_1,
                    cursor,
                    new String[]{LockedInDatabaseHelper.COl_NAME},
                    new int[] {android.R.id.text1},
                    0);

我相信上述方法会奏效。 但是，由于您正在更改数据库的结构，因此您应该在重新运行应用程序之前执行以下操作之一：-

1. 删除/清除应用程序的数据（这实际上会删除数据库）。
2. 卸载应用程序（这也会有效地删除数据库）。