Question

我正在尝试在我的Android应用中使用GPS系统。我正在关注tutorial。

当我试图调用我的javaclass.this时，我在上下文中收到错误怎么做。

这是我的java类

import android.support.v4.app.Fragment;
import com.lifesymb.lifesymb.R;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.RelativeLayout;
import android.widget.Toast;

    public class gps extends Fragment {


         Button btnShowLocation;

            // GPSTracker class
            GPSTracker gps;
            public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {

                if (container == null) {

                    return null;
                }

                RelativeLayout mRelativeLayout = (RelativeLayout) inflater.inflate(R.layout.gps,
                                container, false);



                // note that we're looking for a button with id="@+id/myButton" in your inflated layout
                // Naturally, this can be any View; it doesn't have to be a button


                      // note that we're looking for a button with id="@+id/myButton" in your inflated layout
                    // Naturally, this can be any View; it doesn't have to be a button
                btnShowLocation = (Button) mRelativeLayout.findViewById(R.id.gps1);
             // show location button click event
                btnShowLocation.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View arg0) {        
                        // create class object
                        gps = new GPSTracker(gps.this);

                        // check if GPS enabled     
                        if(gps.canGetLocation()){

                            double latitude = gps.getLatitude();
                            double longitude = gps.getLongitude();

                            // \n is for new line
                            Toast.makeText(getActivity(), "Your Location is - \nLat: " + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show();    
                        }else{
                            // can't get location
                            // GPS or Network is not enabled
                            // Ask user to enable GPS/network in settings
                            gps.showSettingsAlert();
                        }

                    }
                });

Iam在以下行中出错

gps = new GPSTracker(gps.this) ( The constructor GPSTracker(gps) is undefined)

这是我的GPSTracker.java文件

import android.app.AlertDialog;
import android.app.Service;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.os.IBinder;
import android.provider.Settings;
import android.util.Log;

public class GPSTracker extends Service implements LocationListener {

    private final Context mContext;

    // flag for GPS status
    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 = 10; // 10 meters

    // The minimum time between updates in milliseconds
    private static final long MIN_TIME_BW_UPDATES = 1000 * 60 * 1; // 1 minute

    // Declaring a Location Manager
    protected LocationManager locationManager;

    public GPSTracker(Context context) {
        this.mContext = context;
        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;
                // First get location from Network Provider
                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;
    }

    /**
     * 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) {
    }

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

}

那么可以告诉我如何做到这一点。我在Normal类中尝试过，但我无法理解Fragment类的用法。

Answer 1

在片段类中使用getActivity()。

getActivity()返回与此片段关联的Activity。

this指当前上下文。 gps是片段。所以请使用getActivity()

java.lang.Object
   ↳    android.content.Context           // see this
       ↳    android.content.ContextWrapper
           ↳    android.view.ContextThemeWrapper
               ↳    android.app.Activity // see this

和片段

java.lang.Object
   ↳    android.app.Fragment

public class GPSTracker extends Service是一项服务。

你有这个

  gps = new GPSTracker(gps.this)

而是启动服务或将服务绑定到活动。

您可以使用getApplicationContext()

为了让您更好地了解commonsware的详细答案

When to call activity context OR application context?

Answer 2

Fragment不会从Context延伸，因此您无法将Fragment（或因此gps个对象）传入GPSTracker构造函数。但是，您可以在.getActivity()上致电Fragment，以便将{em> 从<{1}}继承的Activity关联起来。

Context

Answer 3

首先，扩展GPSTracker的{{1}}类已经意味着它正在扩展Service ...那么为什么需要参数化的构造函数用于GPSTracker并将Context作为参数？您可以直接在服务中调用Context，也可以使用getApplicationContext()来引用，因为服务是一个上下文。

第二，不推荐（我认为不是一种方法）为this建立参数化构造函数（即使对于Service，Activity等）。如果您有参数化构造函数，则必须定义默认的构造函数。

第三，即使BroadCastReceiver是一个简单的Java类，这也不是手动为Service创建Object（实例）的方法。系统将负责实例化Service

最后，正如其他答案所说，Service不会延伸Fragment。所以你应该使用Context

Android如何在Fragment Class中使用java class.this

3 个答案: