Android - Location Based Services

2021-12-07 14:05 Android开发

<blockquote > Android location APIs make it easy for you to build location-aware applications, without needing to focus on the details of the underlying location technology. </blockquote> This becomes possible with the help ofGoogle Play services, which facilitates adding location awareness to your app with automated location tracking, geofencing, and activity recognition. This tutorial shows you how to use Location Services in your APP to get the current location, get periodic location updates, look up addresses etc. <h2 >The Location Object</h2> TheLocationobject represents a geographic location which can consist of a latitude, longitude, time stamp, and other information such as bearing, altitude and velocity. There are following important methods which you can use with Location object to get location specific information: <table class="table table-bordered" > <tbody > <tr > <th >Sr.No.</th> <th >Method & Description</th> </tr> <tr > <td >1</td> <td >float distanceTo(Location dest) Returns the approximate distance in meters between this location and the given location. </td> </tr> <tr > <td >2</td> <td >float getAccuracy() Get the estimated accuracy of this location, in meters. </td> </tr> <tr > <td >3</td> <td >double getAltitude() Get the altitude if available, in meters above sea level. </td> </tr> <tr > <td >4</td> <td >float getBearing() Get the bearing, in degrees. </td> </tr> <tr > <td >5</td> <td >double getLatitude() Get the latitude, in degrees. </td> </tr> <tr > <td >6</td> <td >double getLongitude() Get the longitude, in degrees. </td> </tr> <tr > <td >7</td> <td >float getSpeed() Get the speed if it is available, in meters/second over ground. </td> </tr> <tr > <td >8</td> <td >boolean hasAccuracy() True if this location has an accuracy. </td> </tr> <tr > <td >9</td> <td >boolean hasAltitude() True if this location has an altitude. </td> </tr> <tr > <td >10</td> <td >boolean hasBearing() True if this location has a bearing. </td> </tr> <tr > <td >11</td> <td >boolean hasSpeed() True if this location has a speed. </td> </tr> <tr > <td >12</td> <td >void reset() Clears the contents of the location. </td> </tr> <tr > <td >13</td> <td >void setAccuracy(float accuracy) Set the estimated accuracy of this location, meters. </td> </tr> <tr > <td >14</td> <td >void setAltitude(double altitude) Set the altitude, in meters above sea level. </td> </tr> <tr > <td >15</td> <td >void setBearing(float bearing) Set the bearing, in degrees. </td> </tr> <tr > <td >16</td> <td >void setLatitude(double latitude) Set the latitude, in degrees. </td> </tr> <tr > <td >17</td> <td >void setLongitude(double longitude) Set the longitude, in degrees. </td> </tr> <tr > <td >18</td> <td >void setSpeed(float speed) Set the speed, in meters/second over ground. </td> </tr> <tr > <td >19</td> <td >String toString() Returns a string containing a concise, human-readable description of this object. </td> </tr> </tbody> </table> <h2 >Get the Current Location</h2> To get the current location, create a location client which isLocationClientobject, connect it to Location Services usingconnect()method, and then call itsgetLastLocation()method. This method returns the most recent location in the form ofLocationobject that contains latitude and longitude coordinates and other information as explained above. To have location based functionality in your activity, you will have to implement two interfaces − <ul class="list" > <li > GooglePlayServicesClient.ConnectionCallbacks </li> <li > GooglePlayServicesClient.OnConnectionFailedListener </li> </ul> These interfaces provide following important callback methods, which you need to implement in your activity class − <table class="table table-bordered" > <tbody > <tr > <th >Sr.No.</th> <th >Callback Methods & Description</th> </tr> <tr > <td >1</td> <td >abstract void onConnected(Bundle connectionHint) This callback method is called when location service is connected to the location client successfully. You will useconnect()method to connect to the location client. </td> </tr> <tr > <td >2</td> <td >abstract void onDisconnected() This callback method is called when the client is disconnected. You will usedisconnect()method to disconnect from the location client. </td> </tr> <tr > <td >3</td> <td >abstract void onConnectionFailed(ConnectionResult result) This callback method is called when there was an error connecting the client to the service. </td> </tr> </tbody> </table> <blockquote >You should create the location client inonCreate()method of your activity class, then connect it inonStart(), so that Location Services maintains the current location while your activity is fully visible. You should disconnect the client inonStop()method, so that when your app is not visible, Location Services is not maintaining the current location. This helps in saving battery power up-to a large extent.</blockquote> <h2 >Get the Updated Location</h2> If you are willing to have location updates, then apart from above mentioned interfaces, you will need to implementLocationListenerinterface as well. This interface provide following callback method, which you need to implement in your activity class − <table class="table table-bordered" > <tbody > <tr > <th >Sr.No.</th> <th >Callback Method & Description</th> </tr> <tr > <td >1</td> <td >abstract void onLocationChanged(Location location) This callback method is used for receiving notifications from the LocationClient when the location has changed. </td> </tr> </tbody> </table> <h2 >Location Quality of Service</h2> TheLocationRequestobject is used to request a quality of service (QoS) for location updates from theLocationClient. There are following useful setter methods which you can use to handle QoS. There are equivalent getter methods available which you can check in Android official documentation. <table class="table table-bordered" > <tbody > <tr > <th >Sr.No.</th> <th >Method & Description</th> </tr> <tr > <td >1</td> <td >setExpirationDuration(long millis) Set the duration of this request, in milliseconds. </td> </tr> <tr > <td >2</td> <td >setExpirationTime(long millis) Set the request expiration time, in millisecond since boot. </td> </tr> <tr > <td >3</td> <td >setFastestInterval(long millis) Explicitly set the fastest interval for location updates, in milliseconds. </td> </tr> <tr > <td >4</td> <td >setInterval(long millis) Set the desired interval for active location updates, in milliseconds. </td> </tr> <tr > <td >5</td> <td >setNumUpdates(int numUpdates) Set the number of location updates. </td> </tr> <tr > <td >6</td> <td >setPriority(int priority) Set the priority of the request. </td> </tr> </tbody> </table> Now for example, if your application wants high accuracy location it should create a location request withsetPriority(int)set to PRIORITY_HIGH_ACCURACY andsetInterval(long)to 5 seconds. You can also use bigger interval and/or other priorities like PRIORITY_LOW_POWER for to request "city" level accuracy or PRIORITY_BALANCED_POWER_ACCURACY for "block" level accuracy. <blockquote >Activities should strongly consider removing all location request when entering the background (for example at onPause()), or at least swap the request to a larger interval and lower quality to save power consumption.</blockquote> <h2 >Displaying a Location Address</h2> Once you haveLocationobject, you can useGeocoder.getFromLocation()method to get an address for a given latitude and longitude. This method is synchronous, and may take a long time to do its work, so you should call the method from thedoInBackground()method of anAsyncTaskclass. TheAsyncTaskmust be subclassed to be used and the subclass will overridedoInBackground(Params...)method to perform a task in the background andonPostExecute(Result)method is invoked on the UI thread after the background computation finishes and at the time to display the result. There is one more important method available in AyncTask which isexecute(Params... params), this method executes the task with the specified parameters. Check following example to have better understanding on how we use AynchTask in any Android application to get work done in the background without interfering main task. <h2 >Example</h2> Following example shows you in practical how to to use Location Services in your app to get the current location and its equivalent addresses etc. <blockquote >To experiment with this example, you will need actual Mobile device equipped with latest Android OS, otherwise you will have to struggle with emulator which may not work.</blockquote> <h3 >Install the Google Play Services SDK</h3> Before you proceed to have location support in your Android Applications, you need to set-upGoogle Play Services SDKusing following simple steps − <table class="table table-bordered" > <tbody > <tr > <th class="fivepct" >Steps</th> <th >Description</th> </tr> <tr > <td >1</td> <td >Launch Android Studio IDE <ul class="list" > <li > From Android Studio selectfile >project structure >dependencies > Click on + button to add dependencies </li> <li >you would get choose library dependencies dialog window</li> </ul> </td> </tr> <tr > <td >2</td> <td >Search forcom.google.android.gms:play-services:6.5.87or higher version library. its depend on which android version is using with.</td> </tr> <tr > <td >3</td> <td >Select the google play services and press apply button as shown below image</td> </tr> </tbody> </table> <h3 >Create Android Application</h3> <table class="table table-bordered" > <tbody > <tr > <th class="fivepct" >Step</th> <th >Description</th> </tr> <tr > <td >1</td> <td >You will use Android studio IDE to create an Android application and name it asTutorialspointunder a packagecom.example.Tutorialspoint. While creating this project, make sure youTarget SDKandCompile Withat the latest version of Android SDK to use higher levels of APIs.</td> </tr> <tr > <td >2</td> <td >AddGoogle Play Servicelibrary in your project by following simple steps given below.</td> </tr> <tr > <td >3</td> <td >Modifysrc/MainActivity.javafile and add required code as shown below to take care of getting current location and its equivalent address.</td> </tr> <tr > <td >4</td> <td >Modify layout XML fileres/layout/activity_main.xmlto add all GUI components which include three buttons and two text views to show location/address.</td> </tr> <tr > <td >5</td> <td >Modifyres/values/strings.xmlto define required constant values</td> </tr> <tr > <td >6</td> <td >ModifyAndroidManifest.xmlas shown below</td> </tr> <tr > <td >7</td> <td >Run the application to launch Android emulator and verify the result of the changes done in the application.</td> </tr> </tbody> </table> Let's addGoogle Play Servicereference in the project.Click on file> project structure > dependencies >and select+and then search google play services which will showcom.google.android.gms:play-services:6.5.87Click on ok button. it will close the choose dependencies windows. you must be close project structure by clicking apply button <img alt="Google Play Service" src="http://www.tutorialspoint.com/android/images/location1.jpg" /> Above image is showing the result of adding google play services to project. after add google play services to project. It should be as follows <img alt="Location" src="http://www.tutorialspoint.com/android/images/location2.jpg" /> Following is the content of the modified main activity filesrc/com.example.Tutorialspoint/MainActivity.java. <pre class="prettyprint notranslate prettyprinted" > package com.example.Tutorialspoint; import java.io.IOException; import java.util.List; import java.util.Locale; import com.google.android.gms.common.ConnectionResult; import com.google.android.gms.common.GooglePlayServicesClient; import com.google.android.gms.location.LocationClient; import android.content.Context; import android.location.Address; import android.location.Geocoder; import android.location.Location; import android.os.AsyncTask; import android.os.Bundle; import android.support.v4.app.FragmentActivity; import android.util.Log; import android.view.View; import android.widget.Button; import android.widget.TextView; import android.widget.Toast; public class MainActivity extends FragmentActivity implements GooglePlayServicesClient.ConnectionCallbacks, GooglePlayServicesClient.OnConnectionFailedListener { LocationClient mLocationClient; private TextView addressLabel; private TextView locationLabel; private Button getLocationBtn; private Button disconnectBtn; private Button connectBtn; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); locationLabel = (TextView) findViewById(R.id.locationLabel); addressLabel = (TextView) findViewById(R.id.addressLabel); getLocationBtn = (Button) findViewById(R.id.getLocation); getLocationBtn.setOnClickListener(new View.OnClickListener() { public void onClick(View view) { displayCurrentLocation(); } }); disconnectBtn = (Button) findViewById(R.id.disconnect); disconnectBtn.setOnClickListener(new View.OnClickListener() { public void onClick(View view) { mLocationClient.disconnect(); locationLabel.setText("Got disconnected...."); } }); connectBtn = (Button) findViewById(R.id.connect); connectBtn.setOnClickListener(new View.OnClickListener() { public void onClick(View view) { mLocationClient.connect(); locationLabel.setText("Got connected...."); } }); // Create the LocationRequest object mLocationClient = new LocationClient(this, this, this); } @Override protected void onStart() { super.onStart(); // Connect the client. mLocationClient.connect(); locationLabel.setText("Got connected...."); } @Override protected void onStop() { // Disconnect the client. mLocationClient.disconnect(); super.onStop(); locationLabel.setText("Got disconnected...."); } @Override public void onConnected(Bundle dataBundle) { // Display the connection status Toast.makeText(this, "Connected", Toast.LENGTH_SHORT).show(); } @Override public void onDisconnected() { // Display the connection status Toast.makeText(this, "Disconnected. Please re-connect.",Toast.LENGTH_SHORT).show(); } @Override public void onConnectionFailed(ConnectionResult connectionResult) { // Display the error code on failure Toast.makeText(this, "Connection Failure : " + connectionResult.getErrorCode(),Toast.LENGTH_SHORT).show(); } public void displayCurrentLocation() { // Get the current location's latitude & longitude Location currentLocation = mLocationClient.getLastLocation(); String msg = "Current Location: " + Double.toString(currentLocation.getLatitude()) + "," + Double.toString(currentLocation.getLongitude()); // Display the current location in the UI locationLabel.setText(msg); // To display the current address in the UI (new GetAddressTask(this)).execute(currentLocation); } /* * Following is a subclass of AsyncTask which has been used to get * address corresponding to the given latitude & longitude. */ private class GetAddressTask extends AsyncTask<Location, Void, String>{ Context mContext; public GetAddressTask(Context context) { super(); mContext = context; } /* * When the task finishes, onPostExecute() displays the address. */ @Override protected void onPostExecute(String address) { // Display the current address in the UI addressLabel.setText(address); } @Override protected String doInBackground(Location... params) { Geocoder geocoder =new Geocoder(mContext, Locale.getDefault()); // Get the current location from the input parameter list Location loc = params[0]; // Create a list to contain the result address <Address> addresses = null; try { addresses = geocoder.getFromLocation(loc.getLatitude(),loc.getLongitude(), 1); } catch (IOException e1) { Log.e("LocationSampleActivity",IO Exception in getFromLocation()); e1.printStackTrace(); return ("IO Exception trying to get address"); } catch (IllegalArgumentException e2) { // Error message to post in the log String errorString = "Illegal arguments " + Double.toString(loc.getLatitude()) +" , " +Double.toString(loc.getLongitude()) +" passed to address service"; Log.e("LocationSampleActivity", errorString); e2.printStackTrace(); return errorString; } // If the reverse geocode returned an address if (addresses != null && addresses.size() > 0) { // Get the first address Address address = addresses.get(0); /* * Format the first line of address (if available), * city, and country name. */ String addressText = String.format("%s, %s, %s"); // If there's a street address, add it address.getMaxAddressLineIndex() > 0 ? address.getAddressLine(0) : "", // Locality is usually a city address.getLocality(), // The country of the address address.getCountryName()); // Return the text return addressText; } else { return "No address found"; } } }// AsyncTask class }</pre> Following will be the content ofres/layout/activity_main.xmlfile − <pre class="prettyprint notranslate prettyprinted" > <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" > <TextView android:id="@+id/textView1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Location Example" android:layout_alignParentTop="true" android:layout_centerHorizontal="true" android:textSize="30dp" /> <TextView android:id="@+id/textView2" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Tutorials point " android:textColor="#ff87ff09" android:textSize="30dp" android:layout_below="@+id/textView1" android:layout_alignRight="@+id/imageButton" android:layout_alignEnd="@+id/imageButton" /> <ImageButton android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/imageButton" android:src="@drawable/abc" android:layout_below="@+id/textView2" android:layout_centerHorizontal="true" /> <Button android:id="@+id/getLocation" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/get_location"/> <Button android:id="@+id/disconnect" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/disconnect"/> <Button android:id="@+id/connect" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/connect"/> <TextView android:id="@+id/locationLabel" android:layout_width="wrap_content" android:layout_height="wrap_content"/> <TextView android:id="@+id/addressLabel" android:layout_width="wrap_content" android:layout_height="wrap_content"/> </LinearLayout></pre> Following will be the content ofres/values/strings.xmlto define two new constants: <pre class="prettyprint notranslate prettyprinted" > <?xml version="1.0" encoding="utf-8"?> <resources> <string name="app_name">Tutorialspoint</string> <string name="action_settings">Settings</string> <string name="hello_world">Hello world!</string> <string name="get_location">Get Location</string> <string name="disconnect">Disconnect Service</string> <string name="connect">Connect Service</string> </resources></pre> Following is the default content ofAndroidManifest.xml− <pre class="prettyprint notranslate prettyprinted" > <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.Tutorialspoint" android:versionCode="1" android:versionName="1.0" > <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/> <application android:allowBackup="true" android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:theme="@style/AppTheme" > <activity android:name="com.example.Tutorialspoint.MainActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest></pre> Let's try to run yourTutorialspointapplication. I assume that, you have connected your actual Android Mobile device with your computer. To run the app from Android Studio, open one of your project's activity files and click Run<img alt="Eclipse Run Icon" class="inline" src="http://www.tutorialspoint.com/android/images/eclipse_run.jpg" />icon from the toolbar. Before starting your application, Android studio installer will display following window to select an option where you want to run your Android application. <img alt="Android Mobile Device" src="http://www.tutorialspoint.com/android/images/location3.jpg" /> Now to see location select Get Location Button which will display location information as follows − <img alt="Android Mobile Location Info" src="http://www.tutorialspoint.com/android/images/location4.jpg" /> You can try by disconnecting location client usingDisconnect Serviceand then connecting it by usingConnect Servicebutton. You can also modify to get location update as explained above and in Android Official documentation.