我正在尝试使用以下链接中的示例获取当前的纬度和经度：http://gabesechansoftware.com/location-tracking/
有两个类：第一个类：
package com.example.marinamapseg;
import android.content.Context;
import android.location.Location;
import android.location.LocationManager;
public class FallbackLocationTracker implements LocationTracker, LocationTracker.LocationUpdateListener {
private boolean isRunning;
private ProviderLocationTracker gps;
private ProviderLocationTracker net;
private LocationUpdateListener listener;
Location lastLoc;
long lastTime;
public FallbackLocationTracker(Context context) {
gps = new ProviderLocationTracker(context, ProviderLocationTracker.ProviderType.GPS);
net = new ProviderLocationTracker(context, ProviderLocationTracker.ProviderType.NETWORK);
}
public void start(){
if(isRunning){
//Already running, do nothing
return;
}
//Start both
gps.start(this);
net.start(this);
isRunning = true;
}
public void start(LocationUpdateListener update) {
start();
listener = update;
}
public void stop(){
if(isRunning){
gps.stop();
net.stop();
isRunning = false;
listener = null;
}
}
public boolean hasLocation(){
//If either has a location, use it
return gps.hasLocation() || net.hasLocation();
}
public boolean hasPossiblyStaleLocation(){
//If either has a location, use it
return gps.hasPossiblyStaleLocation() || net.hasPossiblyStaleLocation();
}
public Location getLocation(){
Location ret = gps.getLocation();
if(ret == null){
ret = net.getLocation();
}
return ret;
}
public Location getPossiblyStaleLocation(){
Location ret = gps.getPossiblyStaleLocation();
if(ret == null){
ret = net.getPossiblyStaleLocation();
}
return ret;
}
public void onUpdate(Location oldLoc, long oldTime, Location newLoc, long newTime) {
boolean update = false;
//We should update only if there is no last location, the provider is the same, or the provider is more accurate, or the old location is stale
if(lastLoc == null){
update = true;
}
else if(lastLoc != null && lastLoc.getProvider().equals(newLoc.getProvider())){
update = true;
}
else if(newLoc.getProvider().equals(LocationManager.GPS_PROVIDER)){
update = true;
}
else if (newTime - lastTime > 5 * 60 * 1000){
update = true;
}
if(update){
lastLoc = newLoc;
lastTime = newTime;
if(listener != null){
listener.onUpdate(lastLoc, lastTime, newLoc, newTime);
}
}
}
}
第二节课：
package com.example.marinamapseg;
import android.content.Context;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
public class ProviderLocationTracker implements LocationListener, LocationTracker {
// The minimum distance to change Updates in meters
private static final long MIN_UPDATE_DISTANCE = 0;
// The minimum time between updates in milliseconds
private static final long MIN_UPDATE_TIME = 0;
private LocationManager lm;
public enum ProviderType{
NETWORK,
GPS
};
private String provider;
private Location lastLocation;
private long lastTime;
private boolean isRunning;
private LocationUpdateListener listener;
public ProviderLocationTracker(Context context, ProviderType type) {
lm = (LocationManager)context.getSystemService(Context.LOCATION_SERVICE);
if(type == ProviderType.NETWORK){
provider = LocationManager.NETWORK_PROVIDER;
}
else{
provider = LocationManager.GPS_PROVIDER;
}
}
public void start(){
if(isRunning){
//Already running, do nothing
return;
}
//The provider is on, so start getting updates. Update current location
isRunning = true;
lm.requestLocationUpdates(provider, MIN_UPDATE_TIME, MIN_UPDATE_DISTANCE,this);
lastLocation = null;
lastTime = 0;
//lm.requestLocationUpdates(provider, MIN_UPDATE_TIME, MIN_UPDATE_DISTANCE,this);
//return;
}
public void start(LocationUpdateListener update) {
start();
listener = update;
}
public void stop(){
if(isRunning){
lm.removeUpdates(this);
isRunning = false;
listener = null;
}
}
public boolean hasLocation(){
if(lastLocation == null){
return false;
}
if(System.currentTimeMillis() - lastTime > 5 * MIN_UPDATE_TIME){
return false; //stale
}
return true;
}
public boolean hasPossiblyStaleLocation(){
if(lastLocation != null){
return true;
}
return lm.getLastKnownLocation(provider)!= null;
}
public Location getLocation(){
if(lastLocation == null){
return null;
}
if(System.currentTimeMillis() - lastTime > 5 * MIN_UPDATE_TIME){
return null; //stale
}
return lastLocation;
}
public Location getPossiblyStaleLocation(){
if(lastLocation != null){
return lastLocation;
}
return lm.getLastKnownLocation(provider);
}
public void onLocationChanged(Location newLoc) {
long now = System.currentTimeMillis();
if(listener != null){
listener.onUpdate(lastLocation, lastTime, newLoc, now);
}
lastLocation = newLoc;
lastTime = now;
}
public void onProviderDisabled(String arg0) {
}
public void onProviderEnabled(String arg0) {
}
public void onStatusChanged(String arg0, int arg1, Bundle arg2) {
}
}
我尝试做的是创建第一个类的对象，并检查是否可以找到位置如下：
fobj=new FallbackLocationTracker(MainActivity.this);
fobj.start();
if(fobj.hasLocation())
{
Location locobj=fobj.getLocation();
current_latitude=locobj.getLatitude();
current_longitude=locobj.getLongitude();
Toast.makeText(getApplicationContext(),current_latitude+" "+current_longitude,Toast.LENGTH_LONG).show();
placemarkersonmap();
}
问题如下：
当lastlocation对象为null时，haslocation（）方法将返回false。但是lastlocation对象只在onlocationchanged方法中获取一个值。所以我如何确保在调用haslocation方法之前运行onlocationchanged方法？
答案 0 :(得分：3)
那么我如何确保在调用我的haslocation方法之前运行onlocationchanged方法？
onLocationChanged()可能永远不会被调用。仅仅因为你想要一个位置并不意味着用户必须允许你获得一个（例如，用户禁用两个提供商）。而且，仅仅因为你想要一个位置并不意味着它在物理上可能得到一个（例如，用户已禁用GPS并启用了飞行模式）。并且，仅仅因为你想要一个位置并不意味着一个人准备就绪。
因此，您的应用程序已经需要处理没有位置的问题，因此请将该逻辑添加到您的应用程序中。
一旦你证明你至少暂时能够获得位置修复，你肯定也会做更多事件驱动的事情，从onLocationChanged()启动一些应用程序逻辑。