Android ListView上的OnitemClick侦听器正在崩溃

您好，我正在创建一个列表，一旦单击列表中的项目，它必须将用户发送到另一个片段，该片段将在我的应用程序中的谷歌地图中具有占位符。我的问题是，当我单击列表中项目上的按钮时，应用程序立即崩溃。我的日志告诉我有一个空异常。我知道我已经在我的观点和听众之间建立了一个参照系，但我希望对这个问题有更深入的了解。 任何帮助都将不胜感激，谢谢

fragment_countries.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" tools:context="myapps.countryapp.Countries"
>

  <ListView
      android:layout_width="fill_parent"
      android:layout_height="fill_parent"
      android:id="@+id/MyListView">
  </ListView>

</FrameLayout>

我的原木猫：

08-26 23:38:38.935    3243-3243/myapps.countryapp E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: myapps.countryapp, PID: 3243
    java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.android.gms.maps.model.Marker com.google.android.gms.maps.GoogleMap.addMarker(com.google.android.gms.maps.model.MarkerOptions)' on a null object reference
            at myapps.countryapp.MyMapFragment.setLocation(MyMapFragment.java:29)
            at myapps.countryapp.Countries$2.onItemClick(Countries.java:78)
            at android.widget.AdapterView.performItemClick(AdapterView.java:305)
            at android.widget.AbsListView.performItemClick(AbsListView.java:1146)
            at android.widget.AbsListView$PerformClick.run(AbsListView.java:3053)
            at android.widget.AbsListView$3.run(AbsListView.java:3860)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5254)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

---

发布你的logcat错误刚刚发布在MyMapFragment.java行号29？？？@Prachi googleMap.AddMarkerMarkropions中的内容；后MyMapFragment xml布局

package myapps.countryapp;

import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.support.v4.app.Fragment;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import com.parse.FindCallback;
import com.parse.ParseObject;
import com.parse.ParseQuery;
import com.squareup.picasso.Picasso;

import java.text.ParseException;
import java.util.ArrayList;
import java.util.List;


/**
 * A simple {@link Fragment} subclass.
 */
public class Countries extends Fragment {
private ListView mListView;


private List<CountriesRetrieved> retrievedCountriesList;


public Countries() {
    // Required empty public constructor
}

    @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View fragmentview = inflater.inflate(R.layout.fragment_countries, container, false);

    mListView = (ListView) fragmentview.findViewById(R.id.MyListView);


        retrievedCountriesList = new ArrayList<>(); //Array of objects.
        ParseQuery<ParseObject> query = ParseQuery.getQuery("Countries"); //name of the database from parse.com
        query.findInBackground(new FindCallback<ParseObject>() {
            //                @Override
            public void done(List<ParseObject> countriesList, com.parse.ParseException e) {
                if (e == null) {
                    for (ParseObject parseObject : countriesList) {
                        String titleOfCountry = (String) parseObject.get("Title");
                        String imageLink = (String) parseObject.get("Image_URL");
                        String latitude = (String) parseObject.get("Latitude");
                        String longitude = (String) parseObject.get("Longitude");
                        CountriesRetrieved countries = new CountriesRetrieved(titleOfCountry, imageLink, latitude, longitude);
                        retrievedCountriesList.add(countries);
                    }
                    mListView.setAdapter(new CountriesAdapterList());
                } else {
                    Log.d("Cannot Parse", "Error: " + e.getMessage());
                }
            }
        });

        mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                CountriesRetrieved crl = retrievedCountriesList.get(position);
                Double lat = Double.parseDouble(crl.getLatitude());
                Double lon = Double.parseDouble(crl.getLongitude());
                MyMapFragment mp = new MyMapFragment();
                mp.setLocation(lat, lon);
            }
        });

    return fragmentview;
}


private class CountriesAdapterList extends BaseAdapter{

    @Override
    public int getCount() {
        return retrievedCountriesList.size(); //This is how the adaptor keeps going, because of the size of list.
    }

    @Override
    public Object getItem(int position) {
        return  retrievedCountriesList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        View rowView = getActivity().getLayoutInflater().inflate(R.layout.row, null);//Instantiates a layout XML file into its corresponding View objects.

        CountriesRetrieved rowCountries = retrievedCountriesList.get(position);

        TextView textViewRow = (TextView) rowView.findViewById(R.id.textAreaList); //Find text view on every row.

        textViewRow.setText(rowCountries.getTitle());

        ImageView imageView = (ImageView) rowView.findViewById(R.id.ImageViewPicasso);
        Picasso.with(getActivity()).load(rowCountries.getImageLink()).into(imageView);

        return rowView;
    }
}

}

package myapps.countryapp;

import android.os.Bundle;

import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.BitmapDescriptorFactory;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

/**
 * Created by user on 8/25/2015.
 */
public class MyMapFragment extends SupportMapFragment {
    GoogleMap googleMap = getMap();

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

}

public void setLocation(Double latitude, Double longitude){
    MarkerOptions markerOptions = new MarkerOptions();

    markerOptions.position(new LatLng(latitude, longitude));
    markerOptions.icon(BitmapDescriptorFactory.fromResource(R.drawable.set_marker));
    googleMap.addMarker(markerOptions);
}

}

08-26 23:38:38.935    3243-3243/myapps.countryapp E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: myapps.countryapp, PID: 3243
    java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.android.gms.maps.model.Marker com.google.android.gms.maps.GoogleMap.addMarker(com.google.android.gms.maps.model.MarkerOptions)' on a null object reference
            at myapps.countryapp.MyMapFragment.setLocation(MyMapFragment.java:29)
            at myapps.countryapp.Countries$2.onItemClick(Countries.java:78)
            at android.widget.AdapterView.performItemClick(AdapterView.java:305)
            at android.widget.AbsListView.performItemClick(AbsListView.java:1146)
            at android.widget.AbsListView$PerformClick.run(AbsListView.java:3053)
            at android.widget.AbsListView$3.run(AbsListView.java:3860)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5254)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)