Question

以下是导致获取空位置的方案：

转到设置 - ＆gt;位置访问。＆gt;关闭WiFi & mobile network location。
打开演示应用。
选择MyLocationDemoActivity。
点击My Location按钮。您将在Toast中获得Location: null。

但是，如果您启用WiFi & mobile network location，则会返回该位置。所以，这里有一些问题：

在我的应用中，我应该假设默认启用WiFi & mobile network location（与演示相同）？
如果没有，如何检测并显示相应的消息？
将网络位置关闭时，最后一个位置（假设是SharedPreference）用于存储是一种很好的做法吗？

这是MyLocationDemoActivity供您参考：

/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.mapdemo;

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesClient.ConnectionCallbacks;
import com.google.android.gms.common.GooglePlayServicesClient.OnConnectionFailedListener;
import com.google.android.gms.location.LocationListener;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationClient;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;

import android.location.Location;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;

/**
 * This demo shows how GMS Location can be used to check for changes to the users location.  The
 * "My Location" button uses GMS Location to set the blue dot representing the users location. To
 * track changes to the users location on the map, we request updates from the
 * {@link LocationClient}.
 */
public class MyLocationDemoActivity extends FragmentActivity
    implements ConnectionCallbacks, OnConnectionFailedListener, LocationListener {

  private GoogleMap mMap;

  private LocationClient mLocationClient;
  private TextView mMessageView;

  // These settings are the same as the settings for the map. They will in fact give you updates at
  // the maximal rates currently possible.
  private static final LocationRequest REQUEST = LocationRequest.create()
      .setInterval(5000)         // 5 seconds
      .setFastestInterval(16)    // 16ms = 60fps
      .setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.my_location_demo);
    mMessageView = (TextView) findViewById(R.id.message_text);
  }

  @Override
  protected void onResume() {
    super.onResume();
    setUpMapIfNeeded();
    setUpLocationClientIfNeeded();
    mLocationClient.connect();
  }

  @Override
  public void onPause() {
    super.onPause();
    if (mLocationClient != null) {
      mLocationClient.disconnect();
    }
  }

  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.map))
             .getMap();
      // Check if we were successful in obtaining the map.
      if (mMap != null) {
        mMap.setMyLocationEnabled(true);
      }
    }
  }

  private void setUpLocationClientIfNeeded() {
    if (mLocationClient == null) {
      mLocationClient = new LocationClient(
          getApplicationContext(),
          this,  // ConnectionCallbacks
          this); // OnConnectionFailedListener
    }
  }

  /**
   * Button to get current Location. This demonstrates how to get the current Location as required,
   * without needing to register a LocationListener.
   */
  public void showMyLocation(View view) {
    if (mLocationClient != null && mLocationClient.isConnected()) {
      String msg = "Location = " + mLocationClient.getLastLocation();
      Toast.makeText(getApplicationContext(), msg, Toast.LENGTH_SHORT).show();
    }
  }

  /**
   * Implementation of {@link LocationListener}.
   */
  @Override
  public void onLocationChanged(Location location) {
    mMessageView.setText("Location = " + location);
  }

  /**
   * Callback called when connected to GCore. Implementation of {@link ConnectionCallbacks}.
   */
  @Override
  public void onConnected(Bundle connectionHint) {
    mLocationClient.requestLocationUpdates(
        REQUEST,
        this);  // LocationListener
  }

  /**
   * Callback called when disconnected from GCore. Implementation of {@link ConnectionCallbacks}.
   */
  @Override
  public void onDisconnected() {
    // Do nothing
  }

  /**
   * Implementation of {@link OnConnectionFailedListener}.
   */
  @Override
  public void onConnectionFailed(ConnectionResult result) {
    // Do nothing
  }
}

Answer 1

以下是如何检测位置的GPS和网络可用性

LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

boolean GPSEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
boolean NetworkEnabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);

不，不要存储最后一个位置。请改用getLastKnownLocation。

Answer 2

最近我遇到了同样的问题。我做了这样的事情：

private boolean posChecked = false;

//import OnMyLocationChangeListener
//from import com.google.android.gms.maps.GoogleMap.OnMyLocationChangeListener; 

@Override
public void OnMyLocationChanged(Location location){

    if(!checked){
        //now your getMyLocation() wont be null
    }

}

您无法确定，getMyLocation()上的OnCreate()会从MapFragment获取非空对象，因为Google {{1}}加载是异步的。

希望这会有所帮助;）

尝试谷歌地图演示时的空位置

2 个答案: