关于gps Location为空值的问题

        tv1=(TextView)findViewById(R.id.textView1);
        tv2=(TextView)findViewById(R.id.textView2);
        tv3=(TextView)findViewById(R.id.textView3);
        locMan = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
getLocationPrivider();
if(mLocation!=null){
// gp1=getGeoByLocation(mLocation);
// if(listmap.size()!=0){
// for(int i=0;i<listmap.size();i++){
// String coordinate=map.get("coordinate");
double gp2_lar=170.1;
double gp2_long=170.2;
double gp1_lar=170.11;
double gp1_long=170.2;
// Location loc=new Location(null);
mLocation.setLatitude(gp2_lar);
mLocation.setLongitude(gp2_long);
gp2=getGeoByLocation(mLocation);
mLocation.setLatitude(gp1_lar);
mLocation.setLongitude(gp1_long);
gp1=getGeoByLocation(mLocation);
double d=getdistance(gp1,gp2);
if(d<=100.00){
tv1.setText(gp1_lar+"."+gp1_long);
tv2.setText(gp2_lar+"."+gp2_long);
tv3.setText("相隔"+d+"米");
}else{
tv1.setText(gp1_lar+"."+gp1_long);
tv2.setText(gp2_lar+"."+gp2_long);
tv3.setText("相隔"+d+"米");
}
// }
// }
}else{
tv1.setText("mLocation为空");
tv2.setText("mLocation为空");
tv3.setText("mLocation为空");
}
/**
 * 取得GeoPoint的方法
 * @param location
 * @return gp
 */
private GeoPoint getGeoByLocation(Location location){
GeoPoint gp=null;
try{
if(location!=null){
double geoLatitude=location.getLatitude()*1E6;
double geoLongitude=location.getLongitude()*1E6;
gp=new GeoPoint((int)geoLatitude,(int)geoLongitude);
}
}catch(Exception e){
e.printStackTrace();
}
return gp;
}
/**
 * 取得LocationProvider
 */
public void getLocationPrivider(){
Criteria mc=new Criteria();
mc.setAccuracy(Criteria.ACCURACY_FINE);
mc.setAltitudeRequired(false);
mc.setBearingRequired(false);
mc.setCostAllowed(true);
mc.setPowerRequirement(Criteria.POWER_LOW);
mLPrivider=locMan.getBestProvider(mc,true);
mLocation=locMan.getLastKnownLocation(mLPrivider);
}/**
 * 获取两点之间距离的方法,得出的距离是m
 */
public double getdistance(GeoPoint gp1,GeoPoint gp2){
double Lat1r=ConvertDegreeToRadians(gp1.getLatitudeE6()/1E6);
double Lat2r=ConvertDegreeToRadians(gp2.getLatitudeE6()/1E6);
double Long1r=ConvertDegreeToRadians(gp1.getLongitudeE6()/1E6);
double Long2r=ConvertDegreeToRadians(gp2.getLongitudeE6()/1E6);
//地球半径(km)
double R=6371;
//计算得出是m
double d=Math.acos(Math.sin(Lat1r)*Math.sin(Lat2r)+Math.cos(Lat1r)*Math.cos(Lat2r)*Math.cos(Long2r-Long1r))*R;
return d;
}
/**
 * ConvertDegreeToRadians
 */
private double ConvertDegreeToRadians(double degrees){
return (Math.PI/180)*degrees;
}
。我的location为空.是什么原因.
ps:有gps权限