Google Maps API v2調用getmap（）拋出NullPointerException（已解決）

Question

我在關注如何使Google Maps API v2正常工作。它顯示了一個地圖片段，但第二個我在一個活動中調用了getmap（），該應用程序崩潰時發生了NullPointerException異常。

這裏是我的RunProgress.java：

package dk.aau.student.runapp; 

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

import android.app.Activity; 
import android.os.Bundle; 
import android.util.Log; 
import android.widget.Toast; 

public class RunProgress extends Activity { 

    // Google Map 
    private GoogleMap googleMap; 

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

    /** 
    * function to load map. If map is not created it will create it for you 
    * */ 
    private void initializeMap() { 
     if (googleMap == null) { 
      googleMap = ((MapFragment) getFragmentManager().findFragmentById(
        R.id.map)).getMap(); 

      // check if map is created successfully or not 
      if (googleMap == null) { 
       Toast.makeText(getApplicationContext(), 
         "Sorry! unable to create maps", Toast.LENGTH_SHORT) 
         .show(); 
      } 
     } 
    } 

    @Override 
    protected void onResume() { 
     super.onResume(); 
     initializeMap(); 
    } 

} 

這裏是layout.xml：

<RelativeLayout 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" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    android:paddingBottom="@dimen/activity_vertical_margin" 
    tools:context="dk.aau.student.runapp.RunProgress$MapFrag"> 

    <fragment 
     android:id="@+id/map" 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:name="com.google.android.gms.maps.MapFragment"/> 

</RelativeLayout> 

這裏是清單：

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

    <uses-sdk 
     android:minSdkVersion="11" 
     android:targetSdkVersion="19" 
     /> 

    <uses-permission android:name="android.permission.INTERNET" /> 
    <uses-permission android:name="com.android.vending.CHECK_LICENSE" /> 
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> 
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> 
    <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-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" > 

       <!-- GOOGLE API KEY --> 
     <meta-data 
      android:name="com.google.android.maps.v2.API_KEY" 
      android:value="API_KEY" /> 
     <meta-data 
      android:name="com.google.android.gms.version" 
      android:value="@integer/google_play_services_version" /> 

     <activity 
      android:name="dk.aau.student.runapp.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> 
     <activity 
      android:name="dk.aau.student.runapp.RunOptions" 
      android:label="@string/title_activity_run_options" 
      android:parentActivityName="dk.aau.student.runapp.MainActivity" > 
      <meta-data 
       android:name="android.support.PARENT_ACTIVITY" 
       android:value="MainActivity" /> 
     </activity> 
     <activity 
      android:name="dk.aau.student.runapp.MatchComp" 
      android:label="@string/title_activity_matchmake" 
      android:parentActivityName="dk.aau.student.runapp.RunOptions" > 
      <meta-data 
       android:name="android.support.PARENT_ACTIVITY" 
       android:value="RunOptions" /> 
     </activity> 
     <activity 
      android:name="dk.aau.student.runapp.MatchFriend" 
      android:label="@string/title_activity_matchmake" 
      android:parentActivityName="dk.aau.student.runapp.RunOptions" > 
      <meta-data 
       android:name="android.support.PARENT_ACTIVITY" 
       android:value="RunOptions" /> 
     </activity> 
     <activity 
      android:name="dk.aau.student.runapp.PickRoute" 
      android:label="@string/title_activity_pick_route" 
      android:parentActivityName="dk.aau.student.runapp.MatchComp" > 
      <meta-data 
       android:name="android.support.PARENT_ACTIVITY" 
       android:value="MatchComp" /> 
     </activity> 
     <activity 
      android:name="dk.aau.student.runapp.RunProgress" 
      android:label="@string/title_activity_run_progress" > 
     </activity> 
    </application> 

</manifest> 

注：我有一個API鍵，我剛剛從這個清單中刪除它。

這裏是我的logcat：

03-28 17:01:48.222: E/AndroidRuntime(12800): FATAL EXCEPTION: main 
03-28 17:01:48.222: E/AndroidRuntime(12800): java.lang.RuntimeException: Unable to resume activity {dk.aau.student.runapp/dk.aau.student.runapp.RunProgress}: java.lang.NullPointerException 
03-28 17:01:48.222: E/AndroidRuntime(12800): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2732) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2760) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2216) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at android.app.ActivityThread.access$600(ActivityThread.java:149) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1300) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at android.os.Handler.dispatchMessage(Handler.java:99) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at android.os.Looper.loop(Looper.java:153) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at android.app.ActivityThread.main(ActivityThread.java:4987) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at java.lang.reflect.Method.invokeNative(Native Method) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at java.lang.reflect.Method.invoke(Method.java:511) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:821) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:584) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at dalvik.system.NativeStart.main(Native Method) 
03-28 17:01:48.222: E/AndroidRuntime(12800): Caused by: java.lang.NullPointerException 
03-28 17:01:48.222: E/AndroidRuntime(12800): at dk.aau.student.runapp.RunProgress.initializeMap(RunProgress.java:28) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at dk.aau.student.runapp.RunProgress.onResume(RunProgress.java:42) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1189) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at android.app.Activity.performResume(Activity.java:5094) 
03-28 17:01:48.222: E/AndroidRuntime(12800): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2718) 
03-28 17:01:48.222: E/AndroidRuntime(12800): ... 12 more 

我老老實實在我束手無策這裏。

Answer 1

我正在將您的解決方案帶出問題並將其放入正確的答案中以協助將來的搜索。

發現問題：在嘗試調用getmap（）之前未創建片段，因爲調用onCreate（）的佈局是activity_run_progress佈局，而不是fragment_run_progress。我已經將contentView設置爲片段佈局，並刪除了Fragment類，因爲我現在不需要它。在Activity中運行一切。

隨着工作的代碼，我的課現在看起來是這樣的：

public class RunProgress extends Activity 
{ 
    private GoogleMap googleMap; 

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

     initializeMap();    

     } 

    /** 
    * function to load map. If map is not created it will create it for you 
    * */ 
    private void initializeMap() 
    { 
     if (googleMap == null) { 
      googleMap = ((MapFragment) getFragmentManager().findFragmentById(
        R.id.map)).getMap(); 

      // check if map is created successfully or not 
      if (googleMap == null) { 
       Toast.makeText(getApplicationContext(), 
         "Sorry! unable to create maps", Toast.LENGTH_SHORT) 
         .show(); 
      } 
     } 
    } 

} 

而且我的佈局是這樣的：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:id="@+id/container" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    android:paddingBottom="@dimen/activity_vertical_margin" 
    tools:context="dk.aau.student.runapp.RunProgress" 
    tools:ignore="MergeRootFrame"> 

    <fragment 
     android:id="@+id/map" 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:name="com.google.android.gms.maps.MapFragment"/> 

    </RelativeLayout>