Question

我正在使用DB browser for SQLite创建一个外部数据库，该文件中的文件名为words_library.db我有一个名为dictionary.db的表，其中包含3 columns：＆＃34; English_lib＆＃34;，＆＃34; German_lib＆＃34;，＆＃34; _id＆＃34;如下图所示（图1）

我要做的是用该数据库填充Recyclerview，但我没有这样做。

JAVA

public void fetchData() //this method is called to populate the RecyclerView
{
    db =new DataBaseHelper(getContext());
    try {

        db.createDataBase();
        db.openDataBase();

    }
    catch (Exception e)
    {
        e.printStackTrace();
    }

    namelist=new LinkedHashMap<>();
    int ii;
    SQLiteDatabase sd = db.getReadableDatabase();
    Cursor cursor = sd.query("dictionary_lib" ,null, null, null, null, null, null);
    ii=cursor.getColumnIndex("_id");
    eng_list=new ArrayList<String>();
    ger_list= new ArrayList<String>();
    id_list= new ArrayList<String>();
    cursor.moveToFirst();
    while (cursor.moveToNext()){
        namelist.put(cursor.getString(ii), cursor.getString(cursor.getColumnIndex("English_lib")));
    }

    Iterator entries = namelist.entrySet().iterator();
    while (entries.hasNext()) {
        Map.Entry thisEntry = (Map.Entry) entries.next();
        id_list.add(String.valueOf(thisEntry.getKey()));
        eng_list.add(String.valueOf(thisEntry.getValue()));
        ger_list.add(String.valueOf(thisEntry.getValue()));
    }

    for (int i = 0; i < eng_list.size(); i++) {
        data.add(new DictObjectModel(eng_list.get(i), ger_list.get(i)));
    }
    adapter = new CustomAdapter(data);
    rv.setAdapter(adapter);
}

LOG

Failed to read row 1, column -1 from a CursorWindow which has 3469 rows, 2 columns.
java.lang.IllegalStateException: Couldn't read row 1, col -1 from CursorWindow.  
Make sure the Cursor is initialized correctly before accessing data from it.

图1：

我拥有的数据库示例和recyclerview应该只显示English_lib和German_lib列

Answer 1

这样做：

1 - 将PK列名称更改为“rowid”而不是“_id”（这将解决很多PK相关问题，而不仅仅是这一个）

2 - 通过添加新变量和列表来更新代码：

public void fetchData()
{
    db = new DataBaseHelper(getContext());
    try {

        db.createDataBase();
        db.openDataBase();

    }
    catch (Exception e)
    {
        e.printStackTrace();
    }

    namelist = new LinkedHashMap<>();
    nmlist = new LinkedHashMap<>();
    int ii;
    SQLiteDatabase sd = db.getReadableDatabase();
    Cursor cursor = sd.query("dictionary_lib" ,new String[]{
            "English_lib", "German_lib", "rowid"
    }, null, null, null, null, null);
    ii=cursor.getColumnIndexOrThrow("rowid");
    eng_list = new ArrayList<String>();
    ger_list = new ArrayList<String>();
    id_list = new ArrayList<String>();
    while (cursor.moveToNext()){
        namelist.put(cursor.getString(ii), cursor.getString(cursor.getColumnIndexOrThrow("English_lib")));
        nmlist.put(cursor.getString(ii), cursor.getString(cursor.getColumnIndexOrThrow("German_lib")));
    }

    Iterator entries = namelist.entrySet().iterator();
    Iterator entrs = nmlist.entrySet().iterator();
    while (entries.hasNext() && entrs.hasNext()) {
        Map.Entry thisEntry = (Map.Entry) entries.next();
        Map.Entry altEntry = (Map.Entry) entrs.next();
        id_list.add(String.valueOf(thisEntry.getKey()));
        eng_list.add(String.valueOf(thisEntry.getValue()));
        ger_list.add(String.valueOf(altEntry.getValue()));
    }

    for (int i = 0; i < id_list.size(); i++) {
        data.add(new DictObjectModel(eng_list.get(i), ger_list.get(i)));
    }
    adapter = new CustomAdapter(data);
    rv.setAdapter(adapter);
}

在Android中使用外部数据库文件

1 个答案: