Android Studio 说数据库是空的，而实际上它不是答案

【问题标题】：Android Studio says database is empty when infact it is notAndroid Studio 说数据库是空的，而实际上它不是
【发布时间】：2018-04-19 23:07:56
【问题描述】：

这是将项目插入我的名为Train_List的数据库的代码\

 SQLiteDatabase db = openOrCreateDatabase( "Train_list.db", SQLiteDatabase.CREATE_IF_NECESSARY , null);
    try {
        final String CREATE_TABLE_TRAIN_LIST = "CREATE TABLE IF NOT EXISTS Train_list ("
                + "Train_name VARCHAR,"
                + "Train_no VARCHAR,"
                + "Train_start VARCHAR,"
                + "Train_end VARCHAR,"
                + "Seats_Available VARCHAR);";
        db.execSQL(CREATE_TABLE_TRAIN_LIST);
        Toast.makeText(admin_manipulation.this, "Table created", Toast.LENGTH_LONG).show();
        String sql = "INSERT or replace INTO Train_list (Train_name, Train_no, Train_start, Train_end, Seats_Available) VALUES('"+str_Train_name + "',' " +str_Train_no + "', '" +str_Train_start+"','" +str_Train_end+"',' " +str_Train_seats +"');";
        try {
            db.execSQL(sql);
            Toast.makeText(admin_manipulation.this, "train no:"+str_Train_no, Toast.LENGTH_SHORT).show();
        }catch(Exception e)
        {
            Toast.makeText(admin_manipulation.this, "Sorry Not Inserted Sucessfully", Toast.LENGTH_SHORT).show();
            Log.d("Error experienced",e.toString());
        }

我观察到没有exceptions 被抛出，logcat 中也没有任何条目。从而使我相信数据成功插入。

这是检索插入的数据的代码：

setContentView(R.layout.activity_display_data);
        Bundle bundle = getIntent().getExtras();
        no_name = (ListView) findViewById(R.id.Disp_list);
        String message = bundle.getString("package");
        String parameter;
        SQLiteDatabase db = openOrCreateDatabase(message, SQLiteDatabase.CREATE_IF_NECESSARY, null);
        SQLiteDatabase db1 = openOrCreateDatabase("Train_list.db", SQLiteDatabase.CREATE_IF_NECESSARY, null);
        Cursor header;
        namer=(TextView)findViewById(R.id.T1);
        try {
            header = db1.rawQuery("Select * From Train_list Where Train_no='"+message.substring(0,(message.length()-3))+ "'", null);
            String temp = header.getString((header.getColumnIndex("Train_name")));
            Toast.makeText(Display_data.this, "blahhh:"+temp, Toast.LENGTH_LONG).show();
            Log.d("Sucess!","temp:"+temp);
            Toast.makeText(Display_data.this, "Gotcha:"+temp , Toast.LENGTH_LONG).show();
            namer.setText("Train Name: " + temp);
        }catch(Exception e)
        {
            Log.d("Final Error",e.toString());
            Toast.makeText(Display_data.this, "Error", Toast.LENGTH_LONG).show();
        }

这会引发异常

D/Final Error: android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0

通过一点谷歌搜索，我知道当null 返回到游标时会引发此错误，我不明白为什么会发生这种情况，任何人都将不胜感激！

【问题讨论】：

如果你在数据库上运行查询 ""Select * From Train_list Where Train_no='"+message.substring(0,(message.length()-3))+ "'""返回任何行？
你应该经常检查光标是否为 !在访问其对象之前为空。 cursor.moveToFirst(); while (!cursor.isAfterLast()) { cursor.getLong(0) } 等
您发布的代码似乎不是产生该特定异常的代码：您从一开始就从未将光标移动到索引 0。
@AmodGokhale 你说的跑步是什么意思？抱歉，我对此有点陌生
如果你有独立的数据库 Train_list.db 并且如果你在那里运行 select * from 命令......它会返回任何记录吗？如果不是，那么您的选择查询不正确

标签： android mysql sqlite android-studio indexoutofboundsexception

【解决方案1】：

好的，我找到了，你需要添加

在您的 rawQuery 语句中

header = db1.rawQuery("Select * From Train_list Where Train_no= ?'"+message.substring(0,(message.length()-3))+ "'", null)

link

【讨论】：

@ArunMani, rawQuery("SELECT Train_name FROM Train_list WHERE Train_no = ?", new String[] {message.substring(0,(message.length()-3)});