java - 当我用抽屉导航实现它时，SupportMapFragment 为空

Question

我恳请您提供任何帮助，我已经为这个问题伤透了两天了，在解决这个问题之前我无法继续:/

嗯，我正在尝试使用抽屉导航实现 GoogleMap，并且我勉强做到了这一点，但效果不太好。

这是我的类和 xml-s，请记住它们中的大部分是自动生成的。

MapFragment.java:

import android.app.Activity;
import android.net.Uri;
import android.os.Bundle;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.UiSettings;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
import android.support.v4.app.Fragment;
import android.widget.Toast;

/**
 * A simple {@link Fragment} subclass.
 * Activities that contain this fragment must implement the
 * {@link MapFragment.OnFragmentInteractionListener} interface
 * to handle interaction events.
 * Use the {@link MapFragment#newInstance} factory method to
 * create an instance of this fragment.
 */
public class MapFragment extends Fragment {

    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER

    // TODO: Rename and change types of parameters


    private OnFragmentInteractionListener mListener;

    private GoogleMap gMap;
    private Double lat, lng;

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment MapFragment.
     */
    // TODO: Rename and change types and number of parameters
    public static MapFragment newInstance() {
        MapFragment fragment = new MapFragment();
        Bundle args = new Bundle();
        args.putString("Map", "map");
        fragment.setArguments(args);
        return fragment;
    }

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

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        /*if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }*/

        setUpMapIfNeeded();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment

       return inflater.inflate(R.layout.fragment_map, container, false);

    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
    }

    // TODO: Rename method, update argument and hook method into UI event
    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        try {
            mListener = (OnFragmentInteractionListener) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onResume(){
        super.onResume();
        setUpMapIfNeeded();
    }


    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }


/*
    @Override
    public void onDestroyView() {
        super.onDestroyView();
        MapFragment f = (MapFragment) getFragmentManager()
                .findFragmentById(R.id.map);
        if (f != null)
            getFragmentManager().beginTransaction().remove(f).commit();
    }
*/

    public void setUpMapIfNeeded(){

        try {
            if (gMap == null)
                gMap = ((SupportMapFragment) getActivity().getSupportFragmentManager().findFragmentById(R.id.map)).getMap();
        }
        catch (NullPointerException e) {
            Toast.makeText(getActivity(), "Error with retrieving map", Toast.LENGTH_LONG).show();
        }

        if (gMap != null) {
            setUpMap();
        }

    }
    public void setUpMap() {

        Toast.makeText(getActivity(),"Setting up map", Toast.LENGTH_LONG);
        gMap.addMarker(new MarkerOptions().position(new LatLng(0, 0)).title("Marker"));
        gMap.getUiSettings().setMyLocationButtonEnabled(true);
        gMap.setMyLocationEnabled(true);
    }

    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        public void onFragmentInteraction(Uri uri);
    }


}

fragment_map.xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <fragment
        xmlns:android="http://schemas.android.com/apk/res/android"
        class="com.google.android.gms.maps.SupportMapFragment"
        android:id="@+id/map"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</RelativeLayout>

MainActivity.java:

import android.app.Activity;

import android.app.ActionBar;
import android.app.AlertDialog;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.content.Context;
import android.content.DialogInterface;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.support.v4.widget.DrawerLayout;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import android.widget.Toast;

import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;


public class MainActivity extends FragmentActivity
        implements MapFragment.OnFragmentInteractionListener,StatsFragment.OnFragmentInteractionListener,NavigationDrawerFragment.NavigationDrawerCallbacks {

    /**
     * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
     */
    private NavigationDrawerFragment mNavigationDrawerFragment;

    /**
     * Used to store the last screen title. For use in {@link #restoreActionBar()}.
     */
    private CharSequence mTitle;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        mNavigationDrawerFragment = (NavigationDrawerFragment)
                getFragmentManager().findFragmentById(R.id.navigation_drawer);
        mTitle = getTitle();



        // Set up the drawer.
        mNavigationDrawerFragment.setUp(
                R.id.navigation_drawer,
                (DrawerLayout) findViewById(R.id.drawer_layout));
    }

    @Override
    public void onNavigationDrawerItemSelected(int position) {
        // update the main content by replacing fragments
        FragmentManager fragmentManager = getSupportFragmentManager();



            switch (position) {
                case 0: {
                    mTitle = getString(R.string.title_section1);
                try {
                    fragmentManager.beginTransaction().replace(R.id.container, MapFragment.newInstance()).commit();
                    break;
                    }
                catch (NullPointerException e) {Toast.makeText(this,"Error retrieving map fragment",Toast.LENGTH_LONG);}
                }



                case 1: {
                    mTitle = getString(R.string.title_section2);
                     fragmentManager.beginTransaction()
                        .replace(R.id.container, StatsFragment.newInstance())
                        .commit();
                    break;
                }
            }




    }

    public void onSectionAttached(int number) {
        switch (number) {
            case 1:
                mTitle = getString(R.string.title_section1);
                break;
            case 2:
                mTitle = getString(R.string.title_section2);
                break;
        }
    }

    public void restoreActionBar() {
        ActionBar actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
        actionBar.setDisplayShowTitleEnabled(true);
        actionBar.setTitle(mTitle);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        if (!mNavigationDrawerFragment.isDrawerOpen()) {
            // Only show items in the action bar relevant to this screen
            // if the drawer is not showing. Otherwise, let the drawer
            // decide what to show in the action bar.
            getMenuInflater().inflate(R.menu.main, menu);
            restoreActionBar();
            return true;
        }
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_about) {
            openHelpDialog();
            return true;
        }

        return super.onOptionsItemSelected(item);
    }


    public void openHelpDialog(){

        new AlertDialog.Builder(this)
                .setTitle("About")
                .setMessage("Pocket Buddy V1.0 \nAuthor : Milos Matic")
                .setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {
                    }
                })
                .setIcon(android.R.drawable.ic_dialog_alert)
                .show();


    }

    @Override
    public void onFragmentInteraction(Uri uri) {

    }
}

Android list

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="aaaaaaaaaaa" >


    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <!-- The following two permissions are not required to use
         Google Maps Android API v2, but are recommended. -->
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>

    <uses-feature
        android:glEsVersion="0x00020000"
        android:required="true"/>

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >

        <meta-data android:name="com.google.android.gms.version"
         android:value="@integer/google_play_services_version" />

        <meta-data
            android:name="com.google.android.maps.v2.API_KEY"
            android:value="I'm a using correct key"/>

        <activity
            android:name="com.shomi.pocketbuddy.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

嗯，主要问题是每次切换到 MapFragment 时我都没有获得 GoogleMap 对象，我设法用 try-catch block 绕过它并且它可以工作，但它不允许我在 map 上设置任何首选项.

例如，setUpMap() 永远不会被调用。

我尝试重新排列我的代码好几次，它仍然是一样的。

我希望能够保存 fragment 状态，然后自由切换而不丢失我的数据(我想根据移动在 map 上绘制，所以不能每次都从头开始绘制)但我不能这样做直到我解决这个问题。

我认为问题在于 Gmap 对象的准备速度不够快，但我不知道如何解决这个问题:/

我的设备是 Nexus 5，运行 Android 5.0

感谢您的每一点帮助。

Answer 1

而不是

gMap = ((SupportMapFragment) getActivity().getSupportFragmentManager().findFragmentById(R.id.map)).getMap();

使用

gMap = ((SupportMapFragment) this.getChildFragmentManager().findFragmentById(R.id.map)).getMap();