android - 使用 GeoPoint 测量步行距离并向用户显示距离

Question

在我的应用程序中，我试图计算一个人步行的距离。为此，我创建了一个 LocationHelper 类，它应该每 30 秒或 10 米获取一次当前 GeoPoint。我已经有一个方法可以返回我知道有效的两个 GeoPoints 之间的距离(以米为单位)，因为我在以前的项目中使用过它。我还有一个名为 WalkActivity 的 Activity ，我在 LocationHelper 中调用方法 getDistance() 并将其显示在 TextView 中，该 TextView 在计时器的帮助下每 30 秒更新一次。请参阅下面的代码。

当我运行我的应用程序时，没有任何显示。无论我走多远，它都会说“你已经走了 0.0 米”。我没有收到任何错误消息。你认为我做错了什么？我搜索并查看了许多示例，但没有发现可以告诉我这里出了什么问题。

我希望这不是一个愚蠢的问题，欢迎任何帮助:)

package Controller;

import com.google.android.maps.GeoPoint;
import android.content.Context;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;

/**
 * Location Helper Class that handles creation of the Location Manager and Location Listener.
 * 
 */
public class LocationHelper{

    private double distance = 0;
    GeoPoint geoPointA;
    GeoPoint geoPointB;

    //location manager and listener
    private LocationManager locationManager;
    private MyLocationListener locationListener;

    /**
     * Constructor for LocationHelper
     * 
     * @param context - The context of the calling activity.
     */
    public LocationHelper(Context context){

        //setup the location manager
        locationManager = (LocationManager)context.getSystemService(Context.LOCATION_SERVICE);

        //create the location listener
        locationListener = new MyLocationListener();

        //setup a callback for when the GPS gets a lock and we receive data
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 30000, 10, locationListener);

    }

    /**
     * Receiving notifications from the Location Manager when they are sent.
     *
     */
    public class MyLocationListener implements LocationListener {


        /**
         * called when the location service reports a change in location
         */
        public void onLocationChanged(Location location) {

            if (geoPointB == null){
                geoPointB = new GeoPoint((int) location.getLatitude(), (int) location.getLongitude());
            }

            //Getting the current GeoPoint.
            geoPointA = new GeoPoint((int) location.getLatitude(), (int) location.getLongitude());

            //Calculating the distance in meters
            distance = distance + nu.placebo.whatsup.util.Geodetics.distance(geoPointA, geoPointB);

            //Making current GeoPoint the previous GeoPoint
            geoPointB = geoPointA;

        }

        //called when the provider is disabled
        public void onProviderDisabled(String provider) {}
        //called when the provider is enabled
        public void onProviderEnabled(String provider) {}
        //called when the provider changes state
        public void onStatusChanged(String provider, int status, Bundle extras) {}
    }

    /**
     * Stop updates from the Location Service.
     */
    public void killLocationServices(){
        locationManager.removeUpdates(locationListener);
    }

    /**
     * Get Distance 
     *
     * @return - The current distance walked.
     */
    public double getDistance(){
        return distance;
    }

    /**
     * Check if a location has been found yet.
     * @return - True if a location has been acquired. False otherwise.
     */
    public Boolean gpsEnabled(){
        return locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
    }   
}

package edu.chl.dat255.sofiase.readyforapet;

import java.util.Timer;
import java.util.TimerTask;
import Controller.LocationHelper;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class WalkActivity extends Activity{

    private TextView displayDistance;
    private int delay = 0;
    private int period = 30000;
    private Timer timer;
    Handler handler = new Handler();

    private LocationHelper location;

    /**
     * On Create method
     * 
     * @param savedInstanceState - bundle
     */
    @Override
    protected void onCreate (Bundle savedInstanceState) {
        super.onCreate (savedInstanceState);
        setContentView(R.layout.walkactivity);
        location = new LocationHelper(this);

        //Checking if the GPS is enabled, else let the user start GPS if wanted.
        if (location.gpsEnabled()){
            Toast.makeText(this, "GPS is Enabled on your devide", Toast.LENGTH_SHORT).show();
        }
        else{
            showGPSDisabledAlert();
        }

        Button startWalking = (Button) findViewById(R.id.startwalking);
        startWalking.setOnClickListener(new OnClickListener() {

            /**
             * Method onClick for the start walking button
             * 
             * @param v - View
             */
            public void onClick (View v){

                try{
                    timer = new Timer();
                    timer.schedule(myTimerTask, delay, period);
                } 
                catch (Exception e){
                    e.printStackTrace();
                }
            }
        }

                );

        Button stopWalking = (Button) findViewById(R.id.stopwalking);
        stopWalking.setOnClickListener(new OnClickListener() {

            /**
             * Method onClick for the stop walking button
             * 
             * @param v - View
             */
            public void onClick (View v){
                timer.cancel();
                location.killLocationServices();
                startActivity(new Intent(WalkActivity.this, PetActivity.class));
            }
        }
                );

    }


    TimerTask myTimerTask = new TimerTask() {

        @Override
        public void run() {
            handler.post(new Runnable() {
                @Override
                public void run() {
                    displayDistance = (TextView) findViewById(R.id.distance);
                    displayDistance.setText("You have walked " + location.getDistance() + " meters so far.");
                }
            });

        }

    };

    /**
     * If GPS is turned off, lets the user either choose to enable GPS or cancel.
     * 
     */
    private void showGPSDisabledAlert(){
        AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);
        alertDialogBuilder.setMessage("GPS is disabled on your device. Would you like to enable it?")
        .setCancelable(false)
        .setPositiveButton("Go to Settings Page To Enable GPS",
                new DialogInterface.OnClickListener(){
            public void onClick(DialogInterface dialog, int id){
                Intent callGPSSettingIntent = new Intent(
                        android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                startActivity(callGPSSettingIntent);
            }
        });
        alertDialogBuilder.setNegativeButton("Cancel",
                new DialogInterface.OnClickListener(){
            public void onClick(DialogInterface dialog, int id){
                dialog.cancel();
            }
        });
        AlertDialog alert = alertDialogBuilder.create();
        alert.show();
    }

}

Answer 1

代码中的一个问题是当您在 onLocationChanged(Location location) 中从 Location 创建 GeoPoint 时。 Location 类中的 getLatitude() 和 getLongitude() 都返回度数，但 GeoPoint 的构造函数采用微度数.这可能会搞砸您的距离计算，因为您的 GeoPoint 坐标可能是 42 度，在 GeoPoint 中结果是 .0000042 度。

此外，您可以尝试通过调试监视器或通过 Toast 消息以某种方式打印当前位置。这将极大地帮助调试过程，因为您可以从那里看到纬度/经度的变化和调试。

注意:我建议更新到 Maps v2，他们更改了很多类并添加了 LatLng，这让事情更容易理解:)