【发布时间】：2016-11-14 11:39:44
【问题描述】：
我正在尝试创建一个小应用程序，它可以定位用户当前所在的 x 和 y 坐标。问题是我在第 143 行不断收到一个空指针异常。
double lon = loc.getLongitude();
我认为我的 getLastKnownLocation() 返回 null。我正在通过虚拟设备运行它。代码如下。
package com.team23.profilebuilder;
import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import android.location.Location;
import android.location.LocationListener;
import android.os.Bundle;
import android.support.v4.app.ActivityCompat;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.util.Log;
import android.location.LocationManager;
import java.util.List;
public class FindLocationActivity extends CustomActivity
{
// Buttons to be used
private Button locButton, saveButton;
// Textview to be displayed / used
private TextView locText, latText, longText, latVal, longVal;
// Location objects
private LocationManager locMan;
private LocationListener locLis;
private Location loc;
private static final String TAG = "FindLocationActivity";
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_find_location);
// Initialise all elements
initialiseUIElements();
initialiseOtherElements();
// Set button listeners
setListeners();
}
private void initialiseUIElements()
{
locButton = (Button) findViewById(R.id.locButton);
saveButton = (Button) findViewById(R.id.saveButton);
locText = (TextView) findViewById(R.id.locText);
latText = (TextView) findViewById(R.id.latText);
longText = (TextView) findViewById(R.id.longText);
latVal = (TextView) findViewById(R.id.latVal);
longVal = (TextView) findViewById(R.id.longVal);
}
private void initialiseOtherElements()
{
// Acquire a reference to the system LocationManager
locMan = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
// Define a listener which responds to location updates
locLis = new LocationListener()
{
// Method called when a new location is found
@Override
public void onLocationChanged(Location location)
{
loc = location;
}
@Override
public void onStatusChanged(String s, int i, Bundle bundle)
{
}
@Override
public void onProviderEnabled(String s)
{
}
@Override
public void onProviderDisabled(String s)
{
}
};
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED)
{
// TODO: Consider calling
// ActivityCompat#requestPermissions
// here to request the missing permissions, and then overriding
// public void onRequestPermissionsResult(int requestCode, String[] permissions,
// int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for ActivityCompat#requestPermissions for more details.
return;
}
// Register the listener with Location Manager to receive updates
locMan.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locLis);
}
private void setListeners()
{
locButton.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View view)
{
findLocation();
}
});
saveButton.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View view)
{
saveLocation();
}
});
}
private void findLocation()
{
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED)
{
// TODO: Consider calling
// ActivityCompat#requestPermissions
// here to request the missing permissions, and then overriding
// public void onRequestPermissionsResult(int requestCode, String[] permissions,
// int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for ActivityCompat#requestPermissions for more details.
return;
}
// Retrieve last known location
loc = locMan.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
// Retrieve values
double lon = loc.getLongitude();
double lat = loc.getLatitude();
// Set TextView values
longVal.setText(Double.toString(lon));
latVal.setText(Double.toString(lat));
}
private void saveLocation()
{
Log.v(TAG, "SaveLocation Method");
}
}
【问题讨论】：
-
像这样检查空值，if(location!=null){ double latitude = location.getLatitude();双经度 = location.getLongitude(); }
-
问题是它是空的，我希望它真正找到位置，我已经知道它是空的，因为这就是导致我的异常的原因。
-
我已经学习了一些教程，这些教程使我达到了这一点，但我现在正在寻找有关我的问题的具体帮助，我已经阅读了 3-4 个不同的教程，它们的解释都不同，我已经被这个问题困扰了好几天了。
标签： android android-studio location