問(wèn)題描述

我想構(gòu)建一個(gè)以獲取用戶當(dāng)前位置為中心的應(yīng)用，然后通過(guò) Google Places API找到他/她附近的興趣點(diǎn)(如酒吧、餐館等)>.

I want to build an app that centers around getting the user's current location and then find points of interest(such as bars,restaurants,etc) that are close to him/her via the Google Places API.

在網(wǎng)上搜索起點(diǎn)時(shí)，我發(fā)現(xiàn)了一些使用 LocationManager 類的教程和其他一些使用 Google Play 服務(wù) 來(lái)查找用戶的教程位置.

Upon searching the web for a place to start I came across some tutorials that use the LocationManager class and some others that use Google Play Services in order to find the users location.

乍一看他們都做同樣的事情，但由于我是新手，所以我有點(diǎn)困惑，我不知道哪種方法最適合我的需要.所以，我想問(wèn)你:

On first sight both of them do the same thing, but since I am new to this I got a little confused and I don't know which method suits my needs the best. So, I want to ask you :

這兩種查找位置的方法(如果有的話)有什么區(qū)別?

推薦答案

Android 上的用戶位置

在 Android 上獲取用戶的位置比在 iOS 上要簡(jiǎn)單一些.要開(kāi)始混淆，有兩種完全不同的方法可以做到這一點(diǎn).第一個(gè)是使用來(lái)自 android.location.LocationListener 的 Android API，第二個(gè)是使用 Google Play Services API com.google.android.gms.location.LocationListener.讓我們來(lái)看看它們.

Getting the user’s location on Android is a little less straightforward than on iOS. To start the confusion, there are two totally different ways you can do it. The first is using Android APIs from android.location.LocationListener, and the second is using Google Play Services APIs com.google.android.gms.location.LocationListener. Let’s go through both of them.

1. Android 的位置 API

Android 的位置 API 使用三個(gè)不同的提供程序來(lái)獲取位置 -

The Android’s location APIs use three different providers to get location -

• LocationManager.GPS_PROVIDER — 此提供程序使用衛(wèi)星確定位置.根據(jù)具體情況，此提供程序可能需要一段時(shí)間才能返回定位信息.
• LocationManager.NETWORK_PROVIDER — 此提供商根據(jù)蜂窩塔和 WiFi 接入點(diǎn)的可用性確定位置.通過(guò)網(wǎng)絡(luò)查找來(lái)檢索結(jié)果.
• LocationManager.PASSIVE_PROVIDER — 此提供程序?qū)⒎祷仄渌峁┏绦蛏傻奈恢?當(dāng)其他應(yīng)用程序或服務(wù)請(qǐng)求位置更新時(shí)，您會(huì)被動(dòng)地接收位置更新，而您自己并沒(méi)有實(shí)際請(qǐng)求位置.

• LocationManager.GPS_PROVIDER — This provider determines location using satellites. Depending on conditions, this provider may take a while to return a location fix.
• LocationManager.NETWORK_PROVIDER — This provider determines location based on availability of cell tower and WiFi access points. Results are retrieved by means of a network lookup.
• LocationManager.PASSIVE_PROVIDER — This provider will return locations generated by other providers. You passively receive location updates when other applications or services request them without actually requesting the locations yourself.

要點(diǎn)是從系統(tǒng)中獲取LocationManager的對(duì)象，實(shí)現(xiàn)LocationListener，調(diào)用requestLocationUpdatesLocationManager.

The gist of it is that you get an object of LocationManager from the system, implement the LocationListener, and call the requestLocationUpdates on the LocationManager.

這是一個(gè)代碼片段:

    LocationManager locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
// Define a listener that responds to location updates
LocationListener locationListener = new LocationListener() {
    public void onLocationChanged(Location location) {
      // Called when a new location is found by the network location provider.
      makeUseOfNewLocation(location);
    }

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

    public void onProviderEnabled(String provider) {}

    public void onProviderDisabled(String provider) {}
  };

// Register the listener with the Location Manager to receive location updates
locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListener);

Google 位置策略 API 指南 很好地解釋了代碼.但他們也提到，在大多數(shù)情況下，通過(guò)使用 谷歌定位服務(wù) API 代替.現(xiàn)在混亂開(kāi)始了！

Google’s API Guide on Location Strategies explains the code pretty nicely. But they also mention that in most cases, you’ll get better battery performance, as well as more appropriate accuracy, by using the Google Location Services API instead. Now the confusion starts!

1. Google 的定位服務(wù) API

Google 的位置服務(wù) API 是 Google Play 服務(wù) APK 的一部分(方法如下設(shè)置它) .它們建立在 Android 的 API 之上.這些 API 提供了一個(gè)融合位置提供者"，而不是上面提到的提供者.該提供程序會(huì)根據(jù)準(zhǔn)確性、電池使用情況等自動(dòng)選擇要使用的底層提供程序.速度很快，因?yàn)槟梢詮牟粩喔滤南到y(tǒng)范圍的服務(wù)中獲取位置.您還可以使用更高級(jí)的功能，例如地理圍欄.

Google’s Location Services API is a part of the Google Play Services APK (here’s how to set it up) . They’re built on top of Android’s API. These APIs provide a "Fused Location Provider" instead of the providers mentioned above. This provider automatically chooses what underlying provider to use, based on accuracy, battery usage, etc. It is fast because you get location from a system-wide service that keeps updating it. And you can use more advanced features such as geofencing.

要使用 Google 的定位服務(wù)，您的應(yīng)用需要連接到 GooglePlayServicesClient.要連接到客戶端，您的活動(dòng)(或片段等)需要實(shí)現(xiàn) GooglePlayServicesClient.ConnectionCallbacks 和 GooglePlayServicesClient.OnConnectionFailedListener 接口.這是一個(gè)示例代碼:

To use the Google’s Location Services, your app needs to connect to the GooglePlayServicesClient. To connect to the client, your activity (or fragment, or so) needs to implement GooglePlayServicesClient.ConnectionCallbacks and GooglePlayServicesClient.OnConnectionFailedListener interfaces. Here’s a sample code:

    public class MyActivity extends Activity implements ConnectionCallbacks, OnConnectionFailedListener {
    LocationClient locationClient;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my);
        locationClient = new LocationClient(this, this, this);
    }

    @Override
    public void onConnected(Bundle bundle) {
    Location location = locationClient.getLastLocation() ;
        Toast.makeText(this, "Connected to Google Play Services", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onDisconnected() {
    Toast.makeText(this, "Connected from Google Play Services.", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {
        // code to handle failed connection
        // this code can be found here — http://developer.android.com/training/location/retrieve-current.html 
    }

• 為什么 locationClient.getLastLocation() 為空?

locationClient.getLastLocation() 從客戶端獲取最后一個(gè)已知位置.但是，F(xiàn)used Location Provider 僅在至少有一個(gè)客戶端連接到它時(shí)才會(huì)維護(hù)后臺(tái)位置.一旦第一個(gè)客戶端連接，它將立即嘗試獲取位置.如果您的活動(dòng)是第一個(gè)連接的客戶端，并且您立即在 onConnected() 中調(diào)用 getLastLocation()，則可能沒(méi)有足夠的時(shí)間讓第一個(gè)位置進(jìn)入.這將導(dǎo)致 location 為 null.

The locationClient.getLastLocation() gets the last known location from the client. However, the Fused Location Provider will only maintain background location if at least one client is connected to it. Once the first client connects, it will immediately try to get a location. If your activity is the first client to connect and you call getLastLocation() right away in onConnected(), that might not be enough time for the first location to come in. This will result in location being null.

要解決這個(gè)問(wèn)題，您必須(不確定地)等待，直到提供者獲取位置，然后調(diào)用 getLastLocation()，這是不可能知道的.另一個(gè)(更好的)選擇是實(shí)現(xiàn) com.google.android.gms.location.LocationListener 接口以接收定期位置更新(并在獲得第一次更新后將其關(guān)閉).

To solve this issue, you have to wait (indeterminately) till the provider gets the location and then call getLastLocation(), which is impossible to know. Another (better) option is to implement the com.google.android.gms.location.LocationListener interface to receive periodic location updates (and switch it off once you get the first update).

    public class MyActivity extends Activity implements ConnectionCallbacks, OnConnectionFailedListener, LocationListener {
    // . . . . . . . . more stuff here 
    LocationRequest locationRequest;
    LocationClient locationClient;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // . . . . other initialization code
        locationClient = new LocationClient(this, this, this);
    locationRequest = new LocationRequest();
    // Use high accuracy
    locationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
        // Set the update interval to 5 seconds
    locationRequest.setInterval(UPDATE_INTERVAL);
        // Set the fastest update interval to 1 second
    locationRequest.setFastestInterval(FASTEST_INTERVAL);
    }
    // . . . . . . . . other methods 
    @Override
    public void onConnected(Bundle bundle) {
        Location location = locationClient.getLastLocation();
        if (location == null)
            locationClient.requestLocationUpdates(locationRequest, this);
        else
            Toast.makeText(getActivity(), "Location: " + location.getLatitude() + ", " + location.getLongitude(), Toast.LENGTH_SHORT).show();
    }
    // . . . . . . . . other methods
    @Override
    public void onLocationChanged(Location location) {
        locationClient.removeLocationUpdates(this);
        // Use the location here!!!
    }

在此代碼中，您正在檢查客戶端是否已經(jīng)擁有最后一個(gè)位置(在 onConnected 中).如果沒(méi)有，您正在請(qǐng)求位置更新，并在收到更新后立即關(guān)閉請(qǐng)求(在 onLocationChanged() 回調(diào)中).

In this code, you’re checking if the client already has the last location (in onConnected). If not, you’re requesting for location updates, and switching off the requests (in onLocationChanged() callback) as soon as you get an update.

注意 locationClient.requestLocationUpdates(locationRequest, this); 必須在 onConnected 回調(diào)中，否則您將收到 IllegalStateException 因?yàn)槟鷮L試在未連接到 Google Play 服務(wù)客戶端的情況下請(qǐng)求位置.

Note that the locationClient.requestLocationUpdates(locationRequest, this); has to be inside the onConnected callback, or else you will get an IllegalStateException because you will be trying to request for locations without connected to the Google Play Services Client.

• 用戶已禁用定位服務(wù)

很多時(shí)候，用戶會(huì)禁用位置服務(wù)(為了節(jié)省電池或隱私原因).在這種情況下，上面的代碼仍然會(huì)請(qǐng)求位置更新，但永遠(yuǎn)不會(huì)調(diào)用 onLocationChanged.您可以通過(guò)檢查用戶是否禁用了定位服務(wù)來(lái)停止請(qǐng)求.

Many times, the user would have location services disabled (to save battery, or privacy reasons). In such a case, the code above will still request for location updates, but onLocationChanged will never get called. You can stop the requests by checking if the user has disabled the location services.

如果您的應(yīng)用要求它們啟用定位服務(wù)，您可能需要顯示一條消息或祝酒詞.不幸的是，無(wú)法檢查用戶是否在 Google 的位置服務(wù) API 中禁用了位置服務(wù).為此，您將不得不求助于 Android 的 API.

If your app requires them to enable location services, you would want to show a message or a toast. Unfortunately, there is no way of checking if the user has disabled location services in Google’s Location Services API. For this, you will have to resort back to Android’s API.

在您的 onCreate 方法中:

    LocationManager manager = (LocationManager) getActivity().getSystemService(Context.LOCATION_SERVICE);
if (!manager.isProviderEnabled(LocationManager.GPS_PROVIDER) && !manager.isProviderEnabled(LocationManager.NETWORK_PROVIDER)) {
    locationEnabled = false;
    Toast.makeText(getActivity(), "Enable location services for accurate data", Toast.LENGTH_SHORT).show();
}
else locationEnabled = true;

并在您的 onConnected 方法中使用 locationEnabled 標(biāo)志，如下所示:

And use the locationEnabled flag in your onConnected method like this:

    if (location != null) {
    Toast.makeText(getActivity(), "Location: " + location.getLatitude() + ", " + location.getLongitude(), Toast.LENGTH_SHORT).show();
}
else if (location == null && locationEnabled) {
    locationClient.requestLocationUpdates(locationRequest, this);
}

更新

文檔更新，LocationClient 被移除，api 支持在對(duì)話框中一鍵開(kāi)啟 GPS:

Document is updated, LocationClient is removed and the api supports to enable GPS with one click from dialog:

task.addOnSuccessListener(this, new OnSuccessListener<LocationSettingsResponse>() {
@Override
public void onSuccess(LocationSettingsResponse locationSettingsResponse) {
    // All location settings are satisfied. The client can initialize
    // location requests here.
    // ...
}
});

task.addOnFailureListener(this, new OnFailureListener() {
    @Override
    public void onFailure(@NonNull Exception e) {
        if (e instanceof ResolvableApiException) {
            // Location settings are not satisfied, but this can be fixed
            // by showing the user a dialog.
            try {
                // Show the dialog by calling startResolutionForResult(),
                // and check the result in onActivityResult().
                ResolvableApiException resolvable = (ResolvableApiException) e;
                resolvable.startResolutionForResult(MainActivity.this,
                        REQUEST_CHECK_SETTINGS);
            } catch (IntentSender.SendIntentException sendEx) {
                // Ignore the error.
            }
        }
    }
});

鏈接 https://developer.android.com/training/location/change-location-settings#prompt

新的定位客戶端:FusedLocationProviderClient

New location client: FusedLocationProviderClient

  private FusedLocationProviderClient fusedLocationClient;

@Override
protected void onCreate(Bundle savedInstanceState) {
    fusedLocationClient = LocationServices.getFusedLocationProviderClient(this);
}

建議通過(guò)https://developer.android.com/training/location 在執(zhí)行任何定位任務(wù)之前.

It is recommended to go through https://developer.android.com/training/location before doing any location tasks.

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