android - checkSelfPermission 空指针 6.0

Question

我在检查权限时遇到问题，在 6.0 中我的调试总是显示为 nullpointer:

我做错了什么

public String getGeolocation(Context context){

    try{        
        int MY_PERMISSION_ACCESS_COURSE_LOCATION = 1000;         

        if ( ContextCompat.checkSelfPermission(context, android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED ) {

            ActivityCompat.requestPermissions(this, new String[]{android.Manifest.permission.ACCESS_COARSE_LOCATION},
                    MY_PERMISSION_ACCESS_COURSE_LOCATION);
        }
        if ( Build.VERSION.SDK_INT >= 23 &&
                ContextCompat.checkSelfPermission( context, android.Manifest.permission.ACCESS_FINE_LOCATION ) != PackageManager.PERMISSION_GRANTED &&
                ContextCompat.checkSelfPermission( context, android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            //return 0 ;
        }
        mLocationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE); // Here is nullpointer
        //Location location = mLocationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
        Location location = mLocationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
        if(location != null && location.getTime() > Calendar.getInstance().getTimeInMillis() - 2 * 60 * 1000) {
            // Do something with the recent location fix
            //  otherwise wait for the update below
        }
        else {
            //mLocationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);
            mLocationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER,  0, 0, this);
        }
    }catch (Exception e){}
return geo;

}

//我用这个方法来获取数据:

public void onLocationChanged(Location location) {
    if (location != null) {
        Log.v("Location Changed", location.getLatitude() + " and " + location.getLongitude());
        geo = ""+location.getLatitude() + " , " + location.getLongitude();
        mLocationManager.removeUpdates(this);
    }
}

Android studio 的错误异常:

java.lang.IllegalStateException: System services not available to Activities before onCreate()

我在哪里调用 getGeolocation() ？

public class AlarmReceiverCustom extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
getGeolocation(context)

Answer 1

您正在为 getGeolocation() 提供上下文，但仍在对象本身上调用 getSystemService()。

您可能想使用您传递的上下文:

mLocationManager = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);

但是你必须考虑Receiver and Process Lifecycle也是:

A BroadcastReceiver object is only valid for the duration of the call to onReceive(Context, Intent). Once your code returns from this function, the system considers the object to be finished and no longer active. [...]

This means that for longer-running operations you will often use a Service in conjunction with a BroadcastReceiver to keep the containing process active for the entire time of your operation.

因此，您最好重新实现应用程序的这一部分并使用服务来更新位置。