Question

我正在开发一款需要使用Google Maps API的应用。我已经处理了这个问题两天了。我正在使用API的第2版，所以我使用的是地图片段。因此，当我尝试从地图片段中获取谷歌地图并将其分配给我的GoogleMap googleMap变量时，它会抛出空指针异常。我猜它在找到存储GoogleMap对象的片段时遇到了麻烦。我几乎尝试了所有东西。我试图将片段放在我的主活动的xml文件中，使用支持映射片段，并以编程方式将片段添加到我的xml文件中。这些解决方案产生了其他问题，但NPE在所有问题中都是一致的。我觉得我现在非常接近，但我需要一些帮助才能最终实现它。

以下是我的GoogleMaps活动代码：

package com.parse.starter;

import android.app.*;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.provider.Settings;
import android.support.v4.app.FragmentActivity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.maps.*;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.model.*;
import com.google.android.gms.maps.SupportMapFragment;
import com.parse.*;
import com.parse.starter.R;

import java.util.List;

public class OutbreakMap extends FragmentActivity implements LocationListener {
    double lat=50;
    double longi=50;
    private LocationManager locationManager;
    private String provider;
    private GoogleMap googleMap;
    Fragment fragment;


    /** Called when the activity is first created. */

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if(isGooglePlayOn())    {
            setContentView(R.layout.map_layout);
        }
        //Add the map fragment
        FragmentManager fragmentManager = getFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        fragment = new com.parse.starter.MapFragment();
        fragmentTransaction.add(R.id.myfragment, fragment);
        fragmentTransaction.commit();

        // Get the location manager
        locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        LocationManager service = (LocationManager) getSystemService(LOCATION_SERVICE);
        boolean enabled = service.isProviderEnabled(LocationManager.GPS_PROVIDER);

         // Check if enabled and if not send user to the GSP settings
         // Better solution would be to display a dialog and suggesting to
        // go to the settings
        if (!enabled) {
            AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);

            // set title
            alertDialogBuilder.setTitle("Turn On Your GPS");

            // set dialog message
            alertDialogBuilder
                    .setMessage("Please turn on your GPS to track sickness in your area!")
                    .setCancelable(false)
                    .setPositiveButton("Yes",new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog,int id) {
                            // if this button is clicked, close
                            // current activity
                            OutbreakMap.this.finish();
                            Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                            startActivity(intent);
                        }
                    })
                    .setNegativeButton("No",new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog,int id) {
                            // if this button is clicked, just close
                            // the dialog box and do nothing
                            dialog.cancel();
                        }
                    });

            // create alert dialog
            AlertDialog alertDialog = alertDialogBuilder.create();

            // show it
            alertDialog.show();

        }
        // Define the criteria how to select the locatioin provider -> use
        // default
        Criteria criteria = new Criteria();
        provider = locationManager.getBestProvider(criteria, false);
        Location location = locationManager.getLastKnownLocation(provider);

        // Initialize the location fields
        if (location != null) {
            System.out.println("Provider " + provider + " has been selected.");
            onLocationChanged(location);
        } else {
            Toast.makeText(getApplicationContext(),"Location not found",Toast.LENGTH_SHORT).show();
        }

        setUpMapIfNeeded();
        googleMap.setMapType(GoogleMap.MAP_TYPE_SATELLITE);
        if(location != null)  {
            lat=location.getLatitude();
            longi=location.getLongitude();
        }

        CameraPosition cameraPosition = new CameraPosition.Builder()
                    .target(new LatLng(lat,longi))      // Sets the center of the map to lat,longi (which is 50,50 if the current location isnt found)
                    .zoom(17)                   // Sets the zoom
                    .build();                   // Creates a CameraPosition from the builder
        googleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));

        UiSettings uiSettings=googleMap.getUiSettings();
        uiSettings.setAllGesturesEnabled(false);
        // Initialize the location fields
        if (location != null) {
            System.out.println("Provider " + provider + " has been selected.");
            onLocationChanged(location);
        } else {
        Toast.makeText(getApplicationContext(),"Couldn't Find Location",Toast.LENGTH_SHORT).show();
        }



        ParseGeoPoint userLoc= new ParseGeoPoint(lat,longi);
        ParseQuery query= new ParseQuery("Outbreak");
        query.whereWithinMiles("location",userLoc,1);
        query.findInBackground(new FindCallback() {
            public void done(List<ParseObject> objects, ParseException e) {
                if (e == null) {
                GetOutbreaks.getOutBreaksNearMe(googleMap,lat,longi,objects);
                Toast.makeText(getApplicationContext(),"Recieved Outbreak Data",Toast.LENGTH_SHORT).show();
                } else {
                    e.printStackTrace();
                    Toast.makeText(getApplicationContext(),"Could Not Download Data",Toast.LENGTH_SHORT).show();
                }
            }

        });


//        moveToPrescription();
//        moveToPrescription();
    }


    /* Request updates at startup */
    @Override
    protected void onResume() {
        super.onResume();
        locationManager.requestLocationUpdates(provider, 400, 1, this);
    }

    /* Remove the locationlistener updates when Activity is paused */
    @Override
    protected void onPause() {
        super.onPause();
        locationManager.removeUpdates(this);
    }

    @Override
    public void onLocationChanged(Location location) {
        int lat = (int) (location.getLatitude());
        int lng = (int) (location.getLongitude());
    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onProviderEnabled(String provider) {
        Toast.makeText(this, "Enabled new provider " + provider,
                Toast.LENGTH_SHORT).show();

    }

    @Override
    public void onProviderDisabled(String provider) {
        Toast.makeText(this, "Disabled provider " + provider,
                Toast.LENGTH_SHORT).show();
    }

    public void moveToPrescription(){
        Intent intent = new Intent(this,Prescription.class);
        startActivity(intent);
    }

    public void setUpMapIfNeeded() {
        if(googleMap==null) {
           googleMap= ((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();

        }
        else {

        }
    }

    public boolean isGooglePlayOn() {
        int status=GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);
        if(status== ConnectionResult.SUCCESS)   {
            return true;
        }
        ((Dialog) GooglePlayServicesUtil.getErrorDialog(status,this,10)).show();
        Toast.makeText(this,"Google Play Services cannot be found", Toast.LENGTH_SHORT).show();
        return false;
    }

}

这是我的活动的xml文件（内部线性布局是地图片段的持有者）：

    <?xml version="1.0" encoding="utf-8"?>

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

    <FrameLayout
            android:id="@+id/mapContainer"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent">
        <LinearLayout
                android:id="@+id/myfragment"
                android:layout_width="match_parent"
                android:layout_weight="4"
                android:layout_height="match_parent" />
    </FrameLayout>
</LinearLayout>

以下是地图片段的xml文件：

<?xml version="1.0" encoding="utf-8"?>

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

最后这是我的Android Manifest：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.parse.starter"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="4" android:targetSdkVersion="15"/>
    <permission
            android:name="com.parse.starter.permission.MAPS_RECEIVE"
            android:protectionLevel="signature"/>
    <uses-permission android:name="com.parse.starter.permission.MAPS_RECEIVE"/>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES"/>
    <!-- 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-permission android:name="android.permission.WAKE_LOCK"/>

    <application
        android:name="ParseApplication"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".ParseStarterProjectActivity"

            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".Register"/>
        <activity android:name=".Login"/>
        <activity android:name=".Home"/>
        <activity android:name=".OutbreakMap"/>
        <activity android:name=".Prescription"/>
        <activity android:name=".MyPrescriptions"/>
        <receiver android:name=".AlarmManagerBroadcastReceiver"></receiver>

        <uses-library android:name="com.google.android.maps"/>
        <meta-data
                android:name="com.google.android.maps.v2.API_KEY"
                android:value="MY API KEY IS HERE"/>
    </application>
    <uses-feature android:glEsVersion="0x00020000" android:required="true"/>

</manifest>

抱歉，我没有LogCat对话框，因为它已被删除，我正在测试的手机属于一个不得不离开的朋友。但它基本上说，在setUpMapIfNeeded();和googleMap= ((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();所在的行上有一个NPE。此外，值得注意的是，在AndroidManifest.xml文件中，它显示“无法解析符号'0x00020000'”，它在最底部显示<uses-feature android:glEsVersion="0x00020000" android:required="true"/>。这并不能阻止应用程序编译和安装。感谢所有的帮助，非常感谢。

Answer 1

很少有事情搞砸了：

在使用FragmentActivity时使用getSupportFragmentManager
如果要按ID查找片段，则它必须存在于布局文件
您想在布局或代码中添加片段（fragment = new com.parse.starter.MapFragment();） - 而不是两者都
究竟是什么com.parse.starter.MapFragment？

编辑：Manifest中也有一些东西......

可能还有更多内容，但我建议从google play services lib中的地图样本等简单项目开始。

编辑2 ：Manifest中的错误信息：

<uses-library android:name="com.google.android.maps"/>是不必要的
<uses-sdk android:minSdkVersion="4"应为8 - 可能是Cannot resolve symbol '0x00020000'

您无法使用xml将片段嵌套在片段内。您只能使用代码实例化嵌套片段并使用getChildFragmentManager。

我仍然没有看到你的MapFragment代码，但如果你真的需要这个额外的片段，请考虑封装：如果Google的MapFragment在你的MapFragment中（最好更改名称），那么你的MapFragment应该做任何与嵌套片段的交互，而不是活动。

Answer 2

使用getSupportFragmentManager

时使用FragmentActivity

如果要按ID查找片段，则必须在布局文件中存在要在布局中添加片段或者在代码中 (fragment = new com.parse.starter.MapFragment();)

注意：不得同时使用

什么是com.parse.starter.MapFragment？

Google Maps API上的Google Maps API Null Pointer Exception

2 个答案: