Example of Using Google Maps Service and GPS in Android

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本文介绍如何在Android应用中集成Google Maps v2服务及GPS定位功能。首先需要在Google API控制台获取API密钥并配置到AndroidManifest文件中。接着通过创建地图视图并在Activity中引用地图片段实现地图显示。同时，文中详细介绍了如何初始化GPS服务并获取经纬度坐标。

Introduction

This tip is about using Google Maps v2 services and GPS in Android.

Background

Please refer to the below mentioned article to setup your eproject in Android Studio.

https://developer.android.com/tools/studio/index.html

Using the Code

The first thing you need to make before use Google maps v2 is get a key for Google:

Navigate to your project in the Google APIs Console.
In the Services page, verify that the "Google Maps Android API v2" is enabled.
In the left navigation bar, click API Access.
In the resulting page, click Create New Android Key...
In the resulting dialog, enter the SHA-1 fingerprint, then a semicolon, then your application's package name. For example:
```
BB:0D:AC:74:D3:21:E1:43:67:71:9B:62:91:AF:A1:66:6E:44:5D:75;com.example.android.mapexample
```
The Google APIs Console responds by displaying Key for Android apps (with certificates) followed by a forty-character API key, for example:
```
AIzaSyBdVl-cTICSwYKrZ95SuvNw7dbMuDt1KG0
```

Set this Key in your Android manifest file:

 <meta-data
            android:name="com.google.android.maps.v2.API_KEY"
            android:value="@string/google_maps_key" />
<string name="google_maps_key" 
templateMergeStrategy="preserve">...your key ...</string>

After that, you can use class com.google.android.gms.maps.GoogleMap.

The steps to use GoogleMaps are:

Create a view activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/mainView">
 
    <fragment
        android:id="@+id/map"
        android:name="com.google.android.gms.maps.MapFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
 
</RelativeLayout>

Create activity MainActivity.java, and reference to @+id/map:

private GoogleMap googleMap; // Might be null if Google Play services APK is not available.

if (googleMap == null) {

    googleMap = ((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();
 
    // check if map is created successfully or not
    if (googleMap == null) {
       Toast.makeText(getApplicationContext(),
                "Sorry! unable to create maps", Toast.LENGTH_SHORT).show();
    }
    else {
        // Changing map type
        //TODO
    }
}

The Toast.makeText action shows a text indicating that the service of Google maps are not available.

The second thing is initialize the GPS:

To do this, we create a class (GpsLocation) that implements LocationListener to manage the logic of Gps.

We have a constructor, with the context and TextView to show Gps Status:

public GpsLocation(Context mContext, TextView gpsStatusTextView) {
    this.mContext = mContext;
    this.gpsStatusTextView = gpsStatusTextView;
    getLocation();
}

A method getLocation that initializes the gps service and obtains gps location:

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

This class has two attributes, latitude and longitude which are initialized in getLocation method.

In MainActivity, we get these values:

gpsLocation = new GpsLocation(this, gpsStatusTextView);
 
if (gpsLocation.canGetLocation()){
    double longitude = gpsLocation.getLongitude();
    double latitude = gpsLocation.getLatitude();
}