来自现有SQLite数据库的GeoPoints

Question

I am trying to populate a map overlay with markers using lat and long from an existing SQLite database. I have found examples where you input the lat and long as part of the method but none where it is populated from the database itself. I presume you use a Cursor to do this but I am not sure how to do it. I have used Cursors to populate ListViews but can not seem to modify the code for the map overlay.

Can anyone point me in the right direction or direct me to a full tutorial?

Here is my code so far, as I am new to this I need examples as can't construct code well yet.

LocationMap2.java

import com.google.android.maps.MapView;

import android.app.Activity;
import android.content.Context;
import android.database.Cursor;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.CursorAdapter;
import android.widget.TextView;

public class LocationMap2 extends Activity {

// we use a string to hold the name of our extra,
// it must include the full package name
public final static String ID_EXTRA = "com.willows.UKBikeTrails._ID";

private AllScotlandHelper dbDataBaseHelper = null;
private Cursor ourCursor = null;

public void onCreate(Bundle savedInstanceState) {
    try {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.map);

        // this is our MapView element, obtained by id from our XML Layout
        MapView mapView = (MapView) findViewById(R.id.mapview);

        // create our database Helper
        dbDataBaseHelper = new AllScotlandHelper(this);
        // we call the create right after initializing the helper, just in
        // case
        // they have never run the app before
        dbDataBaseHelper.createDatabase();
        //
        // open the database!! Our helper now has a SQLiteDatabase database
        // object
        dbDataBaseHelper.openDataBase();
        // get our cursor. A cursor is a pointer to a dataset, in this case
        // a set of results from a database query
        ourCursor = dbDataBaseHelper.getCursor();
        // tell android to start managing the cursor
        // we do this just incase our activity is interrupted or ends, we
        // want the activity
        // to close and deactivate the cursor, as needed
        startManagingCursor(ourCursor);


    } catch (Exception e) {

        // this is the line of code that sends a real message to the Log
        Log.e("ERROR", "ERROR IN CODE: " + e.toString());

        // this is the line that prints out the location
        // the code where the error occurred.
        e.printStackTrace();
    }

}



class DataBaseAdapter extends CursorAdapter {
    DataBaseAdapter(Cursor c) {
        super(LocationMap2.this, c);
    }

    public void bindView(View row, Context ctxt, Cursor c) {
        DataBaseHolder holder = (DataBaseHolder) row.getTag();
        holder.populateFrom(c, dbDataBaseHelper);
    }

    @Override
    public View newView(Context ctxt, Cursor c, ViewGroup parent) {
        LayoutInflater inflater = getLayoutInflater();
        View row = inflater.inflate(R.layout.trail_list, parent, false);
        DataBaseHolder holder = new DataBaseHolder(row);
        row.setTag(holder);
        return (row);
    }
}

static class DataBaseHolder {
    private TextView name = null;

    DataBaseHolder(View row) {
        name = (TextView) row.findViewById(R.id.row);

    }

    void populateFrom(Cursor c, AllScotlandHelper r) {
        name.setText(r.getName(c));
    }

}

}

LocationMapHelper:

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Locale;

import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteQueryBuilder;
import android.util.Log;

class LocationMapHelper extends SQLiteOpenHelper {

//we declare a bunch of useful constants
//they should be pretty obvious what they are!
private static final String DATABASE_PATH = "/data/data/com.willows.UKBikeTrails/databases/";
private static final String DATABASE_NAME = "ukBikeTrails.db";
private static final int SCHEMA_VERSION = 1;
public static final String TABLE_NAME = "trail_type";
public static final String COLUMN_ID = "_id";
public static final String COLUMN_TITLE = "TYPE";

 // BE AWARE - if you make changes to your database using sqlitebrower, you will need to refresh the assets folder in eclipse
public static final String SECOND_TABLE_NAME = "trail";
public static final String SECOND_COLUMN_ID = "_id";
public static final String SECOND_COLUMN_TITLE = "NAME";

public SQLiteDatabase dbSqlite;

private final Context myContext;

public LocationMapHelper (Context context) {
    super(context, DATABASE_NAME, null, SCHEMA_VERSION);
    this.myContext = context;
    // check if exists and copy database from resource
    //createDB();
}

@Override
public void onCreate(SQLiteDatabase db) {
    // check if exists and copy database from resource

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}
public void createDatabase() {
    createDB();
}

private void createDB() {

    boolean dbExist = DBExists();

    if (!dbExist) {

        //By calling the method we create an empty database into the default system location
        //We need this so we can overwrite that database with our database
        this.getReadableDatabase();

        //now we copy the database we included!
        copyDBFromResource();

    }
}

private boolean DBExists() {

    SQLiteDatabase db = null;

    try {
        String databasePath = DATABASE_PATH + DATABASE_NAME;
        db = SQLiteDatabase.openDatabase(databasePath, null,
                SQLiteDatabase.OPEN_READWRITE);
        db.setLocale(Locale.getDefault());
        db.setLockingEnabled(true);
        db.setVersion(1);

    } catch (SQLiteException e) {

        Log.e("SqlHelper", "database not found");

    }

    if (db != null) {

        db.close();

    }

    return db != null ? true : false;

}

private void copyDBFromResource() {

    InputStream inputStream = null;
    OutputStream outStream = null;
    String dbFilePath = DATABASE_PATH + DATABASE_NAME;

    try {

        inputStream = myContext.getAssets().open(DATABASE_NAME);

        outStream = new FileOutputStream(dbFilePath);

        byte[] buffer = new byte[1024];
        int length;
        while ((length = inputStream.read(buffer)) > 0) {
            outStream.write(buffer, 0, length);
        }

        outStream.flush();
        outStream.close();
        inputStream.close();

    } catch (IOException e) {

        throw new Error ("Problem copying database from resource file.");
    }
}

public void openDataBase() throws SQLException {

    String myPath = DATABASE_PATH + DATABASE_NAME;
    dbSqlite = SQLiteDatabase.openDatabase(myPath, null,
            SQLiteDatabase.OPEN_READWRITE);
}

@Override
public synchronized void close() {

    if (dbSqlite !=null)
    {
        dbSqlite.close();
    }
    super.close();
}

//the following two methods return the column you want and it's title (getName)
public Cursor getCursor() {

    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();

    queryBuilder.setTables(TABLE_NAME);

    String[] asColumnsToReturn = new String[] { COLUMN_ID, COLUMN_TITLE };

    //make sure you get your search pass correctly!
    Cursor mCursor = queryBuilder.query(dbSqlite, asColumnsToReturn, null, 
            null, null, null, "_id");
    //the name after the nulls dictates how the results are returned. ie in order of    "column name" 

    return mCursor;
}


public String getName(Cursor c) {
    return(c.getString(1));
    //where 1 refers to COLUMN_TITLE line 11 rows above (0 would be COLUMN_ID and so on)
}

public Cursor getLatLong(String id) {    
    String[] args = null;
    String query = "SELECT _id, LATITUDE,LONGITUDE FROM trail";

    return (getReadableDatabase().rawQuery(query, args));
}

MapItemizedOverlay:

import java.util.ArrayList;
import android.app.AlertDialog;
import android.content.Context;
import android.graphics.drawable.Drawable;
import com.google.android.maps.ItemizedOverlay;
import com.google.android.maps.OverlayItem;

public class MapItemizedOverlay extends ItemizedOverlay<OverlayItem> {
private ArrayList<OverlayItem> mOverlays = new ArrayList<OverlayItem>();
private Context mContext;

public MapItemizedOverlay(Drawable defaultMarker, Context context) {
    super(boundCenterBottom(defaultMarker));
    mContext = context;
}

public void addOverlay(OverlayItem overlay) {
    mOverlays.add(overlay);
    populate();
}

@Override
protected OverlayItem createItem(int i) {
    return mOverlays.get(i);
}

@Override
public int size() {
    return mOverlays.size();
}

@Override
protected boolean onTap(int index) {
    OverlayItem item = mOverlays.get(index);
    AlertDialog.Builder dialog = new AlertDialog.Builder(mContext);
    dialog.setTitle(item.getTitle());
    dialog.setMessage(item.getSnippet());
    dialog.show();
    return true;
}
}

Answer 1

You read your geopoints from the database like any long/int value, and then instantiate GeoPoint objects from the numbers and add them to a Overlay .

Cursor c = getContentResolver().query(... some uri ..., new String[]{"lat", "lon"}, null, null, null);
while (c.moveToNext()) {
  GeoPoint gp = new GeoPoint(c.getInt(c.getColumnIndex("lat")), c.getInt(c.getColumnIndex("lon")));
  .. add to map overlay ...
}