android - 跟随用户的 map View - Android Maps API v2 的 MyLocationOverlay 类型功能

Question

我切换到 Android 版 map v2，并尝试移植以下功能:

使用 MyLocationOverlay，我可以显示设备的当前位置(蓝点)。当用户的位置发生变化并且点到达可见区域的边缘时， map 会实时显示动画，因此点会成为 View 的中心。

在 v2 中，我将 SupportMapFragment 与 getMap().setMyLocationEnabled(true) 一起使用。当前位置显示为一个蓝点(箭头)，但当设备更改位置时， map View 不会移动，并且该点最终会离开 View 。

有什么想法吗？

Answer 1

您需要将 LocationSource 添加到您的 GoogleMap 并响应 onLocationChanged 事件。这是一个简单的类，它询问用户的位置，然后等到用户的位置可用，然后将 map 动画化为以他们的位置为中心。

public class MyLocationMapFragmentActivity extends FragmentActivity implements LocationListener, LocationSource
{
/**
 * Note that this may be null if the Google Play services APK is not available.
 */
private GoogleMap mMap;

private OnLocationChangedListener mListener;
private LocationManager locationManager;

@Override
protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);

    setContentView(R.layout.basic_map);

    locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);

    if(locationManager != null)
    {
        boolean gpsIsEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
        boolean networkIsEnabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);

        if(gpsIsEnabled)
        {
            locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 5000L, 10F, this);
        }
        else if(networkIsEnabled)
        {
            locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 5000L, 10F, this);
        }
        else
        {
            //Show an error dialog that GPS is disabled.
        }
    }
    else
    {
        //Show a generic error dialog since LocationManager is null for some reason
    }

    setUpMapIfNeeded();
}

@Override
public void onPause()
{
    if(locationManager != null)
    {
        locationManager.removeUpdates(this);
    }

    super.onPause();
}

@Override
public void onResume()
{
    super.onResume();

    setUpMapIfNeeded();

    if(locationManager != null)
    {
        mMap.setMyLocationEnabled(true);
    }
}


/**
 * Sets up the map if it is possible to do so (i.e., the Google Play services APK is correctly
 * installed) and the map has not already been instantiated.. This will ensure that we only ever
 * call {@link #setUpMap()} once when {@link #mMap} is not null.
 * <p>
 * If it isn't installed {@link SupportMapFragment} (and
 * {@link com.google.android.gms.maps.MapView
 * MapView}) will show a prompt for the user to install/update the Google Play services APK on
 * their device.
 * <p>
 * A user can return to this Activity after following the prompt and correctly
 * installing/updating/enabling the Google Play services. Since the Activity may not have been
 * completely destroyed during this process (it is likely that it would only be stopped or
 * paused), {@link #onCreate(Bundle)} may not be called again so we should call this method in
 * {@link #onResume()} to guarantee that it will be called.
 */
private void setUpMapIfNeeded() {
    // Do a null check to confirm that we have not already instantiated the map.
    if (mMap == null) 
    {
        // Try to obtain the map from the SupportMapFragment.
        mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.basicMap)).getMap();
        // Check if we were successful in obtaining the map.

        if (mMap != null) 
        {
            setUpMap();
        }

        //This is how you register the LocationSource
        mMap.setLocationSource(this);
    }
}

/**
 * This is where we can add markers or lines, add listeners or move the camera. In this case, we
 * just add a marker near Africa.
 * <p>
 * This should only be called once and when we are sure that {@link #mMap} is not null.
 */
private void setUpMap() 
{
    mMap.setMyLocationEnabled(true);
}

@Override
public void activate(OnLocationChangedListener listener) 
{
    mListener = listener;
}

@Override
public void deactivate() 
{
    mListener = null;
}

@Override
public void onLocationChanged(Location location) 
{
    if( mListener != null )
    {
        mListener.onLocationChanged( location );

        //Move the camera to the user's location once it's available!
        mMap.animateCamera(CameraUpdateFactory.newLatLng(new LatLng(location.getLatitude(), location.getLongitude())));
    }
}

@Override
public void onProviderDisabled(String provider) 
{
    // TODO Auto-generated method stub
    Toast.makeText(this, "provider disabled", Toast.LENGTH_SHORT).show();
}

@Override
public void onProviderEnabled(String provider) 
{
    // TODO Auto-generated method stub
    Toast.makeText(this, "provider enabled", Toast.LENGTH_SHORT).show();
}

@Override
public void onStatusChanged(String provider, int status, Bundle extras) 
{
    // TODO Auto-generated method stub
    Toast.makeText(this, "status changed", Toast.LENGTH_SHORT).show();
}
}

这应该跟随用户，并在 map 发生变化时保持 map 居中 - 如果您只想在用户“离开屏幕”时将 map 居中放在用户身上，那么您可以检查用户的位置在 map 的可见范围内

@Override
public void onLocationChanged(Location location) 
{
    if( mListener != null )
    {
        mListener.onLocationChanged( location );

        LatLngBounds bounds = this.mMap.getProjection().getVisibleRegion().latLngBounds;

        if(!bounds.contains(new LatLng(location.getLatitude(), location.getLongitude())))
        {
             //Move the camera to the user's location if they are off-screen!
             mMap.animateCamera(CameraUpdateFactory.newLatLng(new LatLng(location.getLatitude(), location.getLongitude())));
        }
    }
}

以下是有关该主题的简短文章: Google Maps Android API V2 MyLocation LocationSource and event handling

更新

我编辑了获取用户位置的方式(请参阅 onCreate 中的 locationManager 代码)。我发现使用“getBestProvider”方法并不可靠，而且不能在多个设备上工作。我有几个用户提示他们的设备永远找不到他们的位置，无论我制定的标准多么宽松。看来手动选择 GPS 或网络是通用的。