运行之后手机应用里一片空白，并没有显示设定的TextView，这是为啥
public class MainActivity extends AppCompatActivity {
private TextView positionTextView;
private LocationManager locationManager;
private String provider;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
positionTextView=(TextView)findViewById(R.id.position_text_view);
locationManager=(LocationManager)getSystemService(Context.LOCATION_SERVICE);
//获取所有可用的位置提供器
List<String> providerList=locationManager.getProviders(true);
if (providerList.contains(LocationManager.GPS_PROVIDER)){
provider=LocationManager.GPS_PROVIDER;
}else if (providerList.contains(LocationManager.NETWORK_PROVIDER)){
provider=LocationManager.NETWORK_PROVIDER;
}else {
//当前没有可用的位置提供器时，弹出Toast提示用户
Toast.makeText(this,"No location provider to use", Toast.LENGTH_SHORT).show();
return;
}
Location location=locationManager.getLastKnownLocation(provider);
if (location!=null){
//显示当前设备的位置信息
showLocation(location);
}
locationManager.requestLocationUpdates(provider,5000,1,locationListener);
}
protected void onDestroy(){
super.onDestroy();
if (locationManager!=null){
//关闭程序时将监听器移除
locationManager.removeUpdates(locationListener);
}
}
LocationListener locationListener=new LocationListener() {
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
@Override
public void onLocationChanged(Location location) {
//更新设备当前的位置信息
showLocation(location);
}
};
private void showLocation(Location location){
String currentPosition="latitude is "+ location.getLatitude()+"\n"+"longitude is "+location.getLongitude();
positionTextView.setText(currentPosition);
}
}
