获取纬度和经度?

Question

我正在尝试在我的回收器视图中获取按钮单击的位置。

但是当我单击按钮时，应用程序崩溃，给我这个错误

日志猫 ：

java.lang.NullPointerException: Attempt to invoke virtual method 'android.location.Location android.location.LocationManager.getLastKnownLocation(java.lang.String)' on a null object reference

回收器查看适配器代码 ：

public class RecieverAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> implements Filterable {
Context context;
List<BloodData> data = Collections.emptyList();
List<BloodData> searchData;
LayoutInflater inflater;
RecieverAdapter RAdapter;
LocationManager locationManager;
public RecieverAdapter(RecieveBlood recieveBlood, List<BloodData> data) {
this.context = recieveBlood;
inflater = LayoutInflater.from( context );
this.data = data;
this.RAdapter = this;
searchData = new ArrayList<>( data );
}
@NonNull
@Override
public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
View view = inflater.inflate( R.layout.blood_list, viewGroup, false );
MyHolder holder = new MyHolder(view);
return holder;
}
@Override
public void onBindViewHolder(@NonNull RecyclerView.ViewHolder viewHolder, int i) {
MyHolder myHolder = (MyHolder) viewHolder;
BloodData current = data.get( i );
myHolder.Sr_Num.setText( " "+i );
myHolder.Donar_Name.setText( "Name : "+current.getD_Name() );
myHolder.Donar_Blood_Group.setText( "Blood Group : " +current.getD_blood_group());
myHolder.Donar_Mobile.setText( "Mobile : "+current.getD_Number());
myHolder.Donar_Gender.setText( "Gender : "+current.getD_Gender());
myHolder.location1.setOnClickListener( new View.OnClickListener() {
@Override
public void onClick(View v) {
getLocation();
}
} );
}
void getLocation() {
if (ContextCompat.checkSelfPermission(context, android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(context, android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions( (Activity) context, new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION, android.Manifest.permission.ACCESS_COARSE_LOCATION}, 101);
}else{
Location location = locationManager.getLastKnownLocation( LocationManager.NETWORK_PROVIDER );
if(location != null){
double lati = location.getLatitude();
double longi = location.getLongitude();
Log.e(TAG,"Location :" +lati+ " ,"+longi );
}
}
}

@Override
public int getItemCount() {
return data.size();
}
private class MyHolder extends  RecyclerView.ViewHolder{
TextView Sr_Num,Donar_Name,Donar_Blood_Group,Donar_Mobile,Donar_Gender;
Button location1, location2;
public MyHolder(@NonNull View itemView) {
super( itemView );
Sr_Num = (TextView) itemView.findViewById( R.id.sr_number );
Donar_Name = (TextView) itemView.findViewById( R.id.Donar_Name );
Donar_Blood_Group  =(TextView) itemView.findViewById( R.id.Donar_blood_Group);
Donar_Mobile = (TextView) itemView.findViewById( R.id.Donar_Number );
Donar_Gender = (TextView) itemView.findViewById( R.id.Donar_Gender );
location1 = (Button) itemView.findViewById( R.id.Location1 );
location2 = (Button) itemView.findViewById( R.id.location2 );

}
}
}

我设置了该位置所需的所有权限。

安卓主节文件：

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="nikhil.bloodbank.bloodsupplies">
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>

因此，每当我单击按钮时，应用程序崩溃都会给我该错误。 而且我还手动检查了是否授予了权限。

Answer 1

您尚未初始化位置管理器实例。 更改适配器构造函数，如下所示：

public RecieverAdapter(RecieveBlood recieveBlood, List<BloodData> data) {
this.context = recieveBlood;
inflater = LayoutInflater.from( context );
this.data = data;
this.RAdapter = this;
searchData = new ArrayList<>( data );
//Initialize Location manager
locationManager = (LocationManager) getContext().getSystemService(Context.LOCATION_SERVICE);
}

请注意，使用getLastKnownLocation()可能会返回旧的和过时的位置，如 android 文档中所述：

返回一个位置

，该位置指示来自上一个已知位置的数据 从给定提供程序获取的修补程序。

这可以在不启动提供程序的情况下完成。请注意，这 位置可能已过期，例如，如果设备已打开 关闭并移动到另一个位置。

如果提供程序当前处于禁用状态，则返回 null。

在下面的链接中，关于获取位置的多种方法有很好的解释： https://developer.android.com/guide/topics/location/strategies

更新

我在下面添加了 locationListener 逻辑，但最佳做法是将位置提取代码放在活动或片段中，请记住，当活动或片段关闭时，应删除 locationListener。 使用locationManager.removeUpdates(locationListener)为了删除位置侦听器。

void getLocation() {
if (ContextCompat.checkSelfPermission(context, android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(context, android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions( (Activity) context, new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION, android.Manifest.permission.ACCESS_COARSE_LOCATION}, 101);
}else{
Location location = locationManager.getLastKnownLocation( LocationManager.NETWORK_PROVIDER );
if(location != null){
double lati = location.getLatitude();
double longi = location.getLongitude();
Log.e(TAG,"Location :" +lati+ " ,"+longi );
} else {
boolean isNetworkAvailable = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
if(isNetworkAvailable) fetchCurrentLocation()
else //Redirect user to device settings in order to turn on location service
}
}
}

您应该实现 locationListener，如下所示：

fetchCurrentLocation() {
try {
LocationListener locationListener = new LocationListener() {
@Override
public void onLocationChanged(final Location location) {
if (location != null) {
locationManager.removeUpdates(this);
double lati = location.getLatitude();
double longi = location.getLongitude();
Log.e(TAG,"Location :" +lati+ " ,"+longi );
}
}
@Override
public void onProviderDisabled(String s) {
locationManager.removeUpdates(this);
}
@Override
public void onStatusChanged(String s, int i, Bundle bundle) {
}
@Override
public void onProviderEnabled(String s) {
}
};
locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 500L,30f, locationListener);
} catch (SecurityException e) {
e.printStackTrace();
}
}