Question

我正在尝试在RecyclerView中单击按钮以获取位置。

但是当我单击按钮时，应用程序崩溃，并给我这个错误

Logcat：

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

RecyclerView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。

Android MainFest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许可。

Answer 1

您尚未初始化位置管理器实例。如下更改适配器的构造函数：

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);
}

并被告知，使用getLastKnownLocation()可能会返回旧的和过时的位置，如android docs中所述：

返回一个位置，该位置指示来自最后一个已知位置的数据   从给定的提供程序获得的修复程序。

这可以在不启动提供程序的情况下完成。注意这个   位置可能已过时，例如，如果设备已打开   然后移到另一个位置。

如果当前禁用了提供程序，则返回null。

以下链接中提供了多种获取位置的方法的出色解释： https://developer.android.com/guide/topics/location/strategies

更新

我在下面添加了locationListener逻辑，但是最佳实践是将要获取代码的位置放在活动或片段中，请记住，当活动或片段关闭时，应该删除locationListener。使用locationManager.removeUpdates(locationListener)来删除locationListener。

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
        }
    }
}

您应按以下方式实现locationListener：

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();
            }
}

获得经度和纬度？

1 个答案: