Question

我的SQLite数据库中有5个字段。我想只检索3个字段（id，纬度，经度）来计算与当前位置的相应距离。我是Android编程的初学者，不确定代码。

public class Camera {
// Labels Table Columns names
public static final String KEY_CID = "id";
public static final String KEY_cname = "cameraname";
public static final String KEY_districtid = "district_id";
public static final String KEY_speedlimit = "Speedlimit";
public static final String KEY_lat = "latitude";
public static final String KEY_lng = "longitude";


public int camera_ID;
public String camera_name;
public int district_ID;
public int speedlimit;
public long clat;
public long clng;
//Also contains setters and getters}

以下是我检索纬度和经度的方法：

    public ArrayList< String> getLatLngList(){


    SQLiteDatabase db = dbOpenerCam.getReadableDatabase();
    String query = "SELECT  " +
            Camera.KEY_CID + "," +
            Camera.KEY_lat + "," +
            Camera.KEY_lng +
            " FROM " + Camera.TABLE;


    ArrayList<String> latLngList = new ArrayList<String>();


    Cursor cursor = db.rawQuery(query,null);
    if (cursor.moveToFirst()) {
        do {
            ArrayList<String> camera= new ArrayList<String>();
             camera.add(cursor.getString(cursor.getColumnIndex(Camera.KEY_CID)));
            camera.add(cursor.getString(cursor.getColumnIndex(Camera.KEY_lat)));
            camera.add(cursor.getString(cursor.getColumnIndex(Camera.KEY_lng)));




        } while (cursor.moveToNext());
    }



    cursor.close();
    db.close();
    return latLngList;

}

我如何才能访问纬度和经度来执行计算？谢谢:)）

以下是数据库创建的代码：

  public class DBOpenerCam  extends SQLiteOpenHelper {

private static final int DATABASE_VERSION = 1;

// Database Name
private static final String DATABASE_NAME = "camera2.db";

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

@Override
public void onCreate(SQLiteDatabase db) {


    String CREATE_TABLE_STUDENT = "CREATE TABLE " + Camera.TABLE  + "("
            + Camera.KEY_CID  + " INTEGER PRIMARY KEY AUTOINCREMENT ,"
            + Camera.KEY_cname + " TEXT, "
            + Camera.KEY_districtid + " TEXT, "
            + Camera.KEY_speedlimit + " TEXT, "
            + Camera.KEY_lat + " DECIMAL(7,5), "
            + Camera.KEY_lng + " DECIMAL(7,5))";

    db.execSQL(CREATE_TABLE_STUDENT);

}


@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // Drop older table if existed
    db.execSQL("DROP TABLE IF EXISTS " + Camera.TABLE);

    // Create tables again
    onCreate(db);

}

}

Answer 1

你有带有getter和setter的Camera类，你可以使用同一个类从数据库中检索你的数据。

    public ArrayList< Camera> getLatLngList(){
         ArrayList<Camera> cameraList= new ArrayList<Camera>();
         Cursor cursor = db.rawQuery(query,null);
            if (cursor.moveToFirst()) {
                do {


        Camera camera = new Camera();            
         camera.setKey(cursor.getString(cursor.getColumnIndex(Camera.KEY_CID)));
                    camera.setLat(cursor.getString(cursor.getColumnIndex(Camera.KEY_lat)));
                    camera.setLon(cursor.getString(cursor.getColumnIndex(Camera.KEY_lng)));

        cameraList.add(camera);



                } while (cursor.moveToNext());
            }

    return cameraList; 
}

使用cameraList arraylist进一步使用。希望这能帮助您实现目标。

Answer 2

您犯的第一个错误是您为lat / long插入双值并尝试检索String。下面是代码，它将执行技巧并返回LatLongType对象的ArrayList（或者您可以使用您的Camera类）：

public ArrayList<LatLong> getLatLong(){
    SQLiteDatabase db=this.getReadableDatabase();
    String query = "SELECT  " +
            Camera.KEY_CID + "," +
            Camera.KEY_lat + "," +
            Camera.KEY_lng +
            " FROM " + Camera.TABLE;
    Cursor cursor = db.rawQuery(query,null);
    ArrayList<LatLong> result = new ArrayList<>();
    if (cursor.moveToFirst()) {
        do {
            result.add(new LatLong(cursor.getDouble(cursor.getColumnIndex(Camera.KEY_lat)), cursor.getDouble(cursor.getColumnIndex(Camera.KEY_lng))));
        } while (cursor.moveToNext());
    }

    cursor.close();
    db.close();
    return result;

}

这是LatLong课程：

public class LatLong {

    private double latitude;
    private double longitude;

    public LatLong(double latitude, double longitude) {
        this.latitude = latitude;
        this.longitude = longitude;
    }

    public double getLatitude() {
        return latitude;
    }

    public void setLatitude(double latitude) {
        this.latitude = latitude;
    }

    public double getLongitude() {
        return longitude;
    }

    public void setLongitude(double longitude) {
        this.longitude = longitude;
    }
}

以下是Camera类的解决方案：

public ArrayList<Camera> getLatLong(){
    SQLiteDatabase db=this.getReadableDatabase();
    String query = "SELECT  " +
            Camera.KEY_CID + "," +
            Camera.KEY_lat + "," +
            Camera.KEY_lng +
            " FROM " + Camera.TABLE;
    Cursor cursor = db.rawQuery(query,null);
    ArrayList<Camera> result = new ArrayList<>();
    if (cursor.moveToFirst()) {
        do {
            Camera c = new Camera();
            c.setClat((long)cursor.getDouble(cursor.getColumnIndex(Camera.KEY_lat)));
            c.setClng((long)cursor.getDouble(cursor.getColumnIndex(Camera.KEY_lng)));
            result.add(c);
        } while (cursor.moveToNext());
    }

    cursor.close();
    db.close();
    return result;

}

不确定我在android studio

2 个答案: