Java Android LocationManager:-显示进度对话框时出错

我正在开发一个需要获取用户当前位置的应用程序。我遵循本教程来实现我的目标。这个代码对我来说非常有效，但是在获取坐标时有一些延迟。在获取坐标之前，我想显示一个进度对话框

我在这里发现了一个类似的问题

但我不同意公认的答案。我试过了，但对我不起作用

我的问题是： 1.当应用程序首次启动时GPS设置为on时，ProgressDialog无限。也就是说，它不会拒绝

一旦找到位置坐标，应用程序就会崩溃

错误： 第二个问题是NullPointerException。不知何故，应用程序无法在主活动中找到对话框。（内部onLocationChanged（））

请帮忙

我的代码： 主要活动：-

public class AndroidGPSTrackingActivity extends Activity {

    Button btnShowLocation;

    // GPSTracker class
    GPSTracker gps;
    ProgressDialog dialog;
    TextView tv_addressView;
    Location loc;
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        tv_addressView = (TextView)findViewById(R.id.tv_address);
        btnShowLocation = (Button) findViewById(R.id.btnShowLocation);

        // show location button click event
        btnShowLocation.setOnClickListener(new View.OnClickListener() {

    @Override
public void onClick(View arg0) 
{
if(loc == null)
                    {
                            dialog = ProgressDialog.show(
AndroidGPSTrackingActivity.this,
"Getting Co-ordinates",
"Please Wait ...");
                    }

             });
    }

    @Override
    protected void onResume()
    {
        super.onResume();
        gps = new GPSTracker(getApplicationContext(),AndroidGPSTrackingActivity.this);
        loc = gps.getLocation();
        if(gps.canGetLocation())
         {
            double latitude = gps.getLatitude();
            double longitude = gps.getLongitude();
            Log.d("Got","Lat = "+latitude+"\nLong = "+longitude);
         }
        else
        {
                    gps.showSettingsAlert();
        }

    }

    public void dismissDialog()
    {
        if(dialog.isShowing()) {
            dialog.dismiss();
        }
    }

    public void upDateUI(String result)
    {
        tv_addressView.setText(result);
    }

}

GPSTracker.java

public class GPSTracker extends Service implements LocationListener {

        ProgressDialog dialog;
    private final Context mContext;
boolean isGPSEnabled = false;
    boolean isNetworkEnabled = false;
boolean canGetLocation = false;
Location location; // location
    double latitude; // latitude
    double longitude; // longitude
AndroidGPSTrackingActivity callingActivity;
    private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10;
private static final long MIN_TIME_BW_UPDATES = 1000 * 60 * 1;
protected LocationManager locationManager;


    public GPSTracker(Context context, AndroidGPSTrackingActivity activity) 
{
        this.mContext = context;
                this.callingActivity = activity;
            getLocation();
            }

    public Location getLocation()
 {
        try {
            locationManager = (LocationManager) mContext
                    .getSystemService(LOCATION_SERVICE);

            // getting GPS status
            isGPSEnabled = locationManager
                    .isProviderEnabled(LocationManager.GPS_PROVIDER);

            // getting network status
            isNetworkEnabled = locationManager
                    .isProviderEnabled(LocationManager.NETWORK_PROVIDER);

            if (!isGPSEnabled && !isNetworkEnabled) 
{
                // no network provider is enabled
            } 
else
                    {

                this.canGetLocation = true;
                if (isNetworkEnabled)
                            {
                    locationManager.requestLocationUpdates(
                            LocationManager.NETWORK_PROVIDER,
                            MIN_TIME_BW_UPDATES,
                                MIN_DISTANCE_CHANGE_FOR_UPDATES, `this);
                    Log.d("Network", "Network");
                    if (locationManager != null)
                    {
                        location = locationManager
                                .getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                        if (location != null)
                        {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
                        }
                    }
                }
                // if GPS Enabled get lat/long using GPS Services
                if (isGPSEnabled) {
                    if (location == null) {
                        locationManager.requestLocationUpdates(
                                LocationManager.GPS_PROVIDER,
                                MIN_TIME_BW_UPDATES,
                                MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                        Log.d("GPS Enabled", "GPS Enabled");
                        if (locationManager != null) {
                            location = locationManager
                                    .getLastKnownLocation(LocationManager.GPS_PROVIDER);
                            if (location != null) {
                                latitude = location.getLatitude();
                                longitude = location.getLongitude();
                            }
                        }
                    }
                }

            }

        } catch (Exception e) {
            e.printStackTrace();
        }

        return location;
    }

    public Location returnLocation()
    {
        return location;
    }

    /**
     * Stop using GPS listener
     * Calling this function will stop using GPS in your app
     * */
    public void stopUsingGPS(){
        if(locationManager != null){
            //dialog.dismiss();
            locationManager.removeUpdates(GPSTracker.this);
        }       
    }

    /**
     * Function to get latitude
     * */
    public double getLatitude(){
        if(location != null){
            latitude = location.getLatitude();
        }

        // return latitude
        return latitude;
    }

    /**
     * Function to get longitude
     * */
    public double getLongitude(){
        if(location != null){
            longitude = location.getLongitude();
        }

        // return longitude
        return longitude;
    }

    /**
     * Function to check GPS/wifi enabled
     * @return boolean
     * */
    public boolean canGetLocation()
    {
        return this.canGetLocation;
    }

    /**
     * Function to show settings alert dialog
     * On pressing Settings button will lauch Settings Options
     * */
    public void showSettingsAlert(){
        AlertDialog.Builder alertDialog = new AlertDialog.Builder(callingActivity);

        // Setting Dialog Title
        alertDialog.setTitle("GPS is settings");

        // Setting Dialog Message
        alertDialog.setMessage("GPS is not enabled. Do you want to go to settings menu?");

        // On pressing Settings button
        alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog,int which) {
                Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                mContext.startActivity(intent);
            }
        });

        // on pressing cancel button
        alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
            dialog.cancel();
            }
        });

        // Showing Alert Message
        alertDialog.show();
    }

    @Override
    public void onLocationChanged(Location location) {


       callingActivity.dismissDialog();

    }

    @Override
    public void onProviderDisabled(String provider) {
        stopUsingGPS();
    }

    @Override
    public void onProviderEnabled(String provider) {
    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
    }

    @Override
    public IBinder onBind(Intent arg0) {
        return null;
    }

}

试试这个

公共最终类GPSTracker实现LocationListener{

private final Context mContext;

// flag for GPS status
public boolean isGPSEnabled = false;

// flag for network status
boolean isNetworkEnabled = false;

// flag for GPS status
boolean canGetLocation = false;

Location location; // location
double latitude; // latitude
double longitude; // longitude

// The minimum distance to change Updates in meters
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 1; // 10 meters

// The minimum time between updates in milliseconds
private static final long MIN_TIME_BW_UPDATES = 1; // 1 minute

// Declaring a Location Manager
protected LocationManager locationManager;

public GPSTracker(Context context) {
    this.mContext = context;
    getLocation();
}

/**
 * Function to get the user's current location
 * 
 * @return
 */
public Location getLocation() {
    try {
        locationManager = (LocationManager) mContext
                .getSystemService(Context.LOCATION_SERVICE);

        // getting GPS status
        isGPSEnabled = locationManager
                .isProviderEnabled(LocationManager.GPS_PROVIDER);

        Log.v("isGPSEnabled", "=" + isGPSEnabled);

        // getting network status
        isNetworkEnabled = locationManager
                .isProviderEnabled(LocationManager.NETWORK_PROVIDER);

        Log.v("isNetworkEnabled", "=" + isNetworkEnabled);

        if (isGPSEnabled == false && isNetworkEnabled == false) {
            // no network provider is enabled
        } else {
            this.canGetLocation = true;
            if (isNetworkEnabled) {
                location=null;
                locationManager.requestLocationUpdates(
                        LocationManager.NETWORK_PROVIDER,
                        MIN_TIME_BW_UPDATES,
                        MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                Log.d("Network", "Network");
                if (locationManager != null) {
                    location = locationManager
                            .getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                    if (location != null) {
                        latitude = location.getLatitude();
                        longitude = location.getLongitude();
                    }
                }
            }
            // if GPS Enabled get lat/long using GPS Services
            if (isGPSEnabled) {
                location=null;
                if (location == null) {
                    locationManager.requestLocationUpdates(
                            LocationManager.GPS_PROVIDER,
                            MIN_TIME_BW_UPDATES,
                            MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                    Log.d("GPS Enabled", "GPS Enabled");
                    if (locationManager != null) {
                        location = locationManager
                                .getLastKnownLocation(LocationManager.GPS_PROVIDER);
                        if (location != null) {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
                        }
                    }
                }
            }
        }

    } catch (Exception e) {
        e.printStackTrace();
    }

    return location;
}

/**
 * Stop using GPS listener Calling this function will stop using GPS in your
 * app
 * */
public void stopUsingGPS() {
    if (locationManager != null) {
        locationManager.removeUpdates(GPSTracker.this);
    }
}

/**
 * Function to get latitude
 * */
public double getLatitude() {
    if (location != null) {
        latitude = location.getLatitude();
    }

    // return latitude
    return latitude;
}

/**
 * Function to get longitude
 * */
public double getLongitude() {
    if (location != null) {
        longitude = location.getLongitude();
    }

    // return longitude
    return longitude;
}

/**
 * Function to check GPS/wifi enabled
 * 
 * @return boolean
 * */
public boolean canGetLocation() {
    return this.canGetLocation;
}

/**
 * Function to show settings alert dialog On pressing Settings button will
 * lauch Settings Options
 * */
public void showSettingsAlert() {
    AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);

    // Setting Dialog Title
    alertDialog.setTitle("GPS is settings");

    // Setting Dialog Message
    alertDialog
            .setMessage("GPS is not enabled. Do you want to go to settings menu?");

    // On pressing Settings button
    alertDialog.setPositiveButton("Settings",
            new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    Intent intent = new Intent(
                            Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                    mContext.startActivity(intent);
                }
            });

    // on pressing cancel button
    alertDialog.setNegativeButton("Cancel",
            new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    dialog.cancel();
                }
            });

    // Showing Alert Message
    alertDialog.show();
}

@Override
public void onLocationChanged(Location location) {
}

@Override
public void onProviderDisabled(String provider) {
}

@Override
public void onProviderEnabled(String provider) {
}

@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}

---

}

为什么在

GPSTracker

类中扩展

服务

？在

mContext.startActivity（intent）之前行添加
对话框。取消（）在开始设置活动之前关闭警报@ρ∑ѕρєK:-我想这会在显示设置菜单之前关闭progressdialog。但是当应用程序启动时，请假设GPS已打开。在这种情况下，永远不会调用mContext.startActivity（intent）。在这种情况下，我应该将dialog.discouse（）放在哪里，正如@ρцσρρѕρєK所指出的，您使用的教程代码有问题。GPSTracker是从服务派生的，但从未通过调用活动中的startService（）启动。如果它确实需要作为服务运行，则需要进行更改。如果要将GPSTracker正确地实现为真正的服务，则在构造函数中传递活动并将其保存为成员是不安全的。该活动可能会在服务继续运行时被停止和销毁，给您留下一个无效的引用。@qbix:-太好了！！！完全有道理。。。请你给我指一下正确的方向好吗。一个教程将是伟大的！！！！下面还有一个我想试试的代码。但是再一次。。。该代码在当前形式下运行良好。问题是在显示ProgressDialog时。我的问题是ProgressDialog。我不知道我应该在哪里展示它，什么时候取消它。