如何在Asynctask中使用数据库

Question

我有这个密码

public  ArrayList<StationData> getAllStations(String num1){

    ArrayList<StationData> stationData = new ArrayList<>();


    Cursor cursor = mydb.rawQuery(" select * from   Stations where lines like '%"+num1+"%'   ORDER BY id DESC", null);

    if (cursor.moveToFirst()){
        do {
            int id = cursor.getInt(cursor.getColumnIndex("id"));
            char faName =  (char)(cursor.getColumnIndex("name"));
            char enName = (char) (cursor.getColumnIndex("enName"));
            char lines = (char)(cursor.getColumnIndex("lines"));
            char address = (char) (cursor.getColumnIndex("address"));
            float latitude = cursor.getFloat(cursor.getColumnIndex("latitude"));
            float longitude = cursor.getFloat(cursor.getColumnIndex("longitude"));
            StationData hh = new StationData(id, faName, enName, lines, address, latitude, longitude);

            stationData.add(hh);

        } while (cursor.moveToNext());
        cursor.close();

    }else{

    }
    return stationData;
}

  class MetroLineMaker extends AsyncTask<String,Void,String>{

        MetroDataBase metroDataBase = new MetroDataBase(getApplicationContext());
        ArrayList<StationData> metroData;
        StationData stationData = new StationData();
//        metroData = new ArrayList<>();

        protected void onPreExecute() {

        }

        @Override
        protected String doInBackground(String... strings) {


            metroData = metroDataBase.getAllStations(strings[0]);

            for (int i=0;i<metroData.size()-1 ;i++) {

                LatLng last = new LatLng(metroData.get(i).getLatitude(), metroData.get(i).getLongitude());
                LatLng next = new LatLng(metroData.get(i + 1).getLatitude(), metroData.get(i + 1).getLongitude());

//                    createMarker(metroData.get(i).getLatitude(), metroData.get(i).getLongitude());


                mMap.addMarker(new MarkerOptions()
                        .position(new LatLng(metroData.get(i).getLatitude(), metroData.get(i).getLongitude()))
                        .anchor(0.5f, 0.5f)
                        .icon(BitmapDescriptorFactory.fromResource(R.mipmap.ic_metro_line_one)));


                mMap.addPolyline(
                        new PolylineOptions().add(
                                last, next
                        ).width(10).color(Color.RED)
                );


            }


            return null;
        }

        protected void onPostExecute(String result) {

        }
    }

E/AndroidRuntime：致命异常：AsyncTask#1进程：com.arnaway.metromap,pid：9493 java.lang.RuntimeException：在Android.os.AsyncTask$3执行doInBackground（）时出错。done(AsyncTask.java:353)在java.util.concurrent.FutureTask.FinishCompletion(futureTask.java:383)在java.util.concurrent.FutureTask.SetExcepthtml" target="_blank">ion(futureTask.java:252)在index=0（位于com.arnaway.metromap.mainactivity$metrolinemaker.doinbackground(mainactivity.java:1028)（位于com.arnaway.metromap.mainactivity$metrolinemaker.doinbackground(mainactivity.java:1013)（位于android.os.asynctask$2)。call(asynctask.java:333)（位于java.util.concurrent.futuretask.run(futuretask.java:266)（位于在java.util.concurrent.ThreadPoolExecutor.RunWorker（ThreadPoolExecutor.java:1162） 在java.util.concurrent.ThreadPoolExecutor$worker.run(ThreadPoolExecutor.java:636) 在java.lang.Thread.Run（Thread.java：764）

我如何在一个异步任务中使用我的数据库并在MainActivity中显示我的标记我的异步任务也在MainActivity中。

Answer 1

我没有数据库方面的经验，但是你的其他代码在一个活动中在哪里呢？你在哪里申报mydb？似乎您的数组列表metroData没有被填充，所以它给出了数组越界错误。

你的getAllStations方法在哪里？在metroDataBase类中？那么这个类的代码在哪里呢？