Android的sqlite的行数始终为零？

问题描述

我使用GUI来创建一个在它1650记录的数据库。

I've used the GUI to create a DB which has 1650 records in it.

我试图查询这个数据库，但它总是返回什么。我试着写一个简单的 getrowcount（）方法，看看是否我得到任何东西，但它总是返回零。我必须在这里失去了一些东西很明显，如果有人可以帮助指出，这是怎么回事。

I'm trying to query this DB but it's always returning nothing. I've tried writing a simple getrowcount() method to see if I'm getting anything at all, but it always returns zero. I must be missing something obvious here, if someone can help point out what's going on.

在我的主 app.java ：

    db = new DbHandler(this);
    String sIcao1 = "ROW COUNT = " + String.valueOf(db.getRowCount());

在我的 dbhandler.java ：

package com.jammo.mywidget4;

<snip - standard includes>

public class DbHandler extends SQLiteOpenHelper {

    private static SQLiteDatabase db;
    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "airports";
    private static final String TABLE_AIRPORTS = "airports";

    public DbHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);

        db = this.getWritableDatabase();
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db = this.getWritableDatabase();
    }

    int getRowCount() {

        int nCount = -1;
        //SQLiteDatabase db = this.getReadableDatabase();
        Cursor cur = db.rawQuery("SELECT * FROM airports", null);
        nCount = cur.getCount();
        if (cur != null) {
            //cur.moveToFirst();
            //nCount = cur.getInt(0);
            //if (cur.getInt (0) == 0) {

            //}
        }

        return nCount;
    }

}

在GUI（SQLite的DB浏览器）我做了一个简单

In the GUI (SQLite DB Browser) I'm doing a simple

select * from airports

......，我找回完整的行数。当我调试Java，光标返回任何内容。

... and I'm getting back the full number of rows. When I debug the Java, cursor returns nothing.

此外，由GUI创建的数据块位于的myapp /资产/ airports.db 。

Also, the DB created by the GUI is located in myapp/assets/airports.db.

任何想法？

推荐答案

我认为你需要包括 .db的在DATABASE_NAME。

I think you need to include the .db in the DATABASE_NAME.

尝试改变这一点：

private static final String DATABASE_NAME = "airports";

这样：

private static final String DATABASE_NAME = "airports.db";

编辑：

其实我觉得即使有这样的变化，它不会为你工作。 SQLiteOpenHelper期待您的数据库文件是 /data/data/your.package/databases / 里面的所以我认为你需要，如果你将其从资产复制到那里希望它与未修改SQLiteOpenHelper工作。

Actually I think even with this change it is not going to work for you. SQLiteOpenHelper is expecting your db file to be inside of /data/data/your.package/databases/ So I think you'll need to copy it from assets to there if you want it to work with an unmodified SQLiteOpenHelper.

请参阅这里了解如何过来复制：Android:访问资产文件夹.sqlite扩展SQLite数据库文件

See here to learn how to copy it over: Android: Accessing assets folder sqlite database file with .sqlite extension

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