需要一些帮助。我正在创建一个应用程序，我从gps或网络提供商处获取位置更新。如果没有启用gps，那么我给了按钮以启用gps。现在我需要做的是从gps获取更新，如果gps无法获得信号，那么我切换到网络提供商并进行位置更新，一旦gps可用，再次切换到gps并计算距离用户已经旅行过。我有多个问题。
getProvider和getBestProvider方法有什么作用？我认为它提供了手机可用的最佳提供商（如果我错了，请纠正我）以及如何使用它来获取位置更新。
我需要知道用户启动应用时启用了哪些提供商。我怎样才能做到这一点？我使用了isProviderEnabled，但在启用或禁用wifi时却感到困惑，它什么都没给我。
如果未启用gps，我尝试了一些条件，然后切换到网络提供商，但这没有做任何事情。我阅读了很多关于此的帖子，但无法弄清楚如何在我的代码中使用它。任何帮助将不胜感激。谢谢。这是我的代码。
public class MainActivity extends Activity {
public boolean getLocation() {
try {
isGps_enabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
} catch (Exception ex) {
}
try {
isNetwork_enabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
} catch (Exception ex) {
}
//don't start listeners if no provider is enabled
if (!isGps_enabled && !isNetwork_enabled)
return false;
if (isGps_enabled)
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
if (isNetwork_enabled)
locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListener);
return true;
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
accu = (TextView) findViewById(R.id.accu);
speed1 = (TextView)findViewById(R.id.speed);
t = (TextView)findViewById(R.id.t);
prevLatLon = (TextView) findViewById(R.id.prevLatLon);
distance = (TextView)findViewById(R.id.distance);
listView = (ListView)findViewById(R.id.listView);
listText = (TextView)findViewById(R.id.listText);
settings = (Button)findViewById(R.id.settings_button);
settings.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
startActivity(intent);
}
});
locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
criteria = new Criteria();
criteria.setAccuracy(Criteria.ACCURACY_FINE);
List<String> providers = locationManager.getProviders(criteria, true);
for (String provider: providers){
distance.setText("Providers: " + provider);
}
provider = locationManager.getBestProvider(criteria, false);
/*isGps_enabled = locationManager.isProviderEnabled(provider);
Toast.makeText(this, isGps_enabled + "", Toast.LENGTH_SHORT).show();
isNetwork_enabled = locationManager.isProviderEnabled(provider);
Toast.makeText(this, isNetwork_enabled + "", Toast.LENGTH_SHORT).show();*/
locationListener = new LocationListener() {
@Override
public void onLocationChanged(Location loc) {
//locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListener);
getLocation();
int accuracy = (int) loc.getAccuracy();
speed = (int) loc.getSpeed();
accu.setText("Accuracy: " + accuracy);
speed1.setText("Speed: " + speed);
t.setText("Time: " + loc.getTime());
listView.setAdapter(new ArrayAdapter<String>(MainActivity.this, R.layout.activity_simplelist, R.id.listText, list));
DateFormat format = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss");
Date date = new Date(loc.getTime());
String formatted = format.format(date);
if (flag == 0) {
latitude = loc.getLatitude();
longitude = loc.getLongitude();
speed = (int) loc.getSpeed();
time = formatted;
distanceInMeters = 0;
distanceTo = 0;
distanceBetween = 0;
timestamp = loc.getTime();
timestampmsec = 0;
hours = 0;
minutes = 0;
seconds = 0;
startTime = loc.getTime();
flag = 1;
list.add("latitude: " + latitude + " longitude: " + longitude +
" \nspeed: " + speed + " Time: " + time + "\nDistance: " + distanceInMeters + " meters"
+ "\ntimestamp: " + timestamp);
}
else {
prevLatitude = latitude;
prevLongitude = longitude;
prevSpeed = speed;
prevTime = time;
prevDistanceInMeters = distanceInMeters;
prevDistanceTo = distanceTo;
prevDistanceBetween = distanceBetween;
//prevTimestamp = timestamp;
prevTimestampmsec = timestampmsec;
prevHours = hours;
prevMinutes = minutes;
prevSeconds = seconds;
prevLatLon.setText("Previous Latitude: " + prevLatitude + "\nPrevious Longitude: " + prevLongitude +
" \nPrevious speed: " + prevSpeed + " \nTime: " + prevTime + "\nPrevious Timestamp: " + prevTimestamp);
latitude = loc.getLatitude();
longitude = loc.getLongitude();
speed = (int) loc.getSpeed();
time = formatted;
timestamp = loc.getTime();
if (loc.hasSpeed()) {
Toast.makeText(MainActivity.this, "true", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(MainActivity.this, "false", Toast.LENGTH_SHORT).show();
}
getDistance();
distanceTo = androidDistanceTo(prevLatitude, prevLongitude, latitude, longitude);
Location.distanceBetween(prevLatitude, prevLongitude, latitude, longitude, results);
distanceBetween = results[0];
list.add("latitude: " + latitude + " longitude: " + longitude +
" \nspeed: " + speed + " Time: " + time + "\nDistance: " + distanceInMeters + " meters"
+ "\nTimestamp: " + timestamp);
speed = prevSpeed + speed;
distanceInMeters = prevDistanceInMeters + distanceInMeters;
distanceTo = prevDistanceTo + distanceTo;
distanceBetween = prevDistanceBetween + distanceBetween;
timestampmsec = (long) (timestamp - startTime);
seconds = TimeUnit.MILLISECONDS.toSeconds(timestampmsec);
if(seconds >= 60) {
minutes = (int) seconds / 60;
seconds = seconds % 60;
}
if(minutes >= 60){
hours = (int) minutes / 60;
minutes = minutes % 60;
}
}
distance.setText("Distance: " + distanceInMeters + " meters" + "\nDistanceTo: " + distanceTo + " meters" +
"\nDistanceBetween: " + distanceBetween + " meters" + "\nTime: " + hours + " hours " +
minutes + " minutes " + seconds + " seconds");
Toast.makeText(MainActivity.this, "Location Changed", Toast.LENGTH_SHORT).show();
}
@Override
public void onProviderDisabled(String arg0) {
//TODO auto generated method stub
Toast.makeText(MainActivity.this, provider + " disabled", Toast.LENGTH_SHORT).show();
}
@Override
public void onProviderEnabled(String arg0) {
//TODO auto generated method stub
Toast.makeText(MainActivity.this, provider + " enabled", Toast.LENGTH_SHORT).show();
}
@Override
public void onStatusChanged(String arg0, int arg1, Bundle arg2) {
//TODO auto generated method stub
}
};
}
public void getDistance(){
double dLat = Math.toRadians(latitude - prevLatitude);
double dLon = Math.toRadians(longitude - prevLongitude);
double a = Math.sin(dLat / 2) * Math.sin(dLat / 2)
+ Math.cos(Math.toRadians(prevLatitude))
* Math.cos(Math.toRadians(latitude)) * Math.sin(dLon / 2)
* Math.sin(dLon / 2);
double c = 2 * Math.asin(Math.sqrt(a));
distanceInMeters = (6372800 * c);
}
public static double androidDistanceTo(double lat_a, double lng_a, double lat_b, double lng_b) {
Location locationA = new Location("Point A");
locationA.setLatitude(lat_a);
locationA.setLongitude(lng_a);
Location locationB = new Location("Point B");
locationB.setLatitude(lat_b);
locationB.setLongitude(lng_b);
return (locationA.distanceTo(locationB));
}
public void resetButton(View view) {
list.clear();
listView.setAdapter(new ArrayAdapter<String>(MainActivity.this, R.layout.activity_simplelist, R.id.listText, list));
}
@Override
protected void onResume() {
super.onResume();
locationManager.requestLocationUpdates(provider, 30000, 0, locationListener);
}
@Override
protected void onPause() {
super.onPause();
//locationManager.removeUpdates(locationListener);
}
答案 0 :(得分：1)
getBestProvider执行以下操作：
返回最符合给定条件的提供程序的名称。 仅允许通过调用访问的提供程序 活动将被退回。如果有几家提供商符合标准，那么 返回最准确的一个。如果没有提供商满足 标准，标准按以下顺序放宽：功率要求，精度，方位，速度，高度
getProvider执行以下操作：
返回与该位置提供者关联的信息 给定名称，如果该名称不存在提供者，则返回null。
以外行人的术语，您选择getProvider的提供者，系统选择提供者getBestProvider
启动监听器的代码看起来很好。但是，您实际上不会在getLocation()和onResume()之外的任何地方拨打onLocationChanged()您需要将该呼叫从onLocationChanged()移出并将其置于onCreate()的末尾}