使用GoogleMap V2時Android應用程序崩潰

Question

Im在GoogleMap中存在一個煩人的問題。我測試過了，地圖顯示正常。但是現在我想設置「我的位置已啓用」，以便地圖自動啓動在電話所在的位置。現在每次運行應用程序都會崩潰。我注意到，當我使用語法GoogleMap時，應用程序崩潰。 我試圖找出這個問題，並沒有結果環顧四周。

這裏是我的Maps.java文件：

package test.test; 

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

import android.location.Location; 
import android.location.LocationListener; 
import android.os.Bundle; 
import android.support.v4.app.FragmentActivity; 

public class Maps extends FragmentActivity implements LocationListener{ 

    GoogleMap googlemap; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     // TODO Auto-generated method stub 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.maps); 
     SupportMapFragment mf = (SupportMapFragment)  getSupportFragmentManager().findFragmentById(R.id.map); 
     googlemap = mf.getMap(); 

     googlemap.setMyLocationEnabled(true); 
     googlemap.setMapType(GoogleMap.MAP_TYPE_NORMAL); 

    } 

Maps.xml：

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:orientation="vertical" > 

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

</LinearLayout> 

最後我androidmanifest：

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

     <uses-sdk 
      android:minSdkVersion="8" 
      android:targetSdkVersion="16" /> 

     <permission 
      android:name="test.test.permission.MAPS_RECEIVE" 
      android:protectionLevel="signature" /> 

     <uses-permission android:name="test.test.permission.MAPS_RECEIVE" /> 
     <uses-permission android:name="android.permission.INTERNET" /> 
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> 
     <uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES" /> 
     <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 

.... 
<meta-data 
      android:name="com.google.android.maps.v2.API_KEY" 
      android:value="my key is here" /> 
    </application> 

以下是錯誤日誌：

FATAL EXCEPTION: main 
java.lang.RuntimeException: Unable to start activity ComponentInfo{test.test/test.test.Maps}: java.lang.NullPointerException 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
at android.app.ActivityThread.access$600(ActivityThread.java:141) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
at android.os.Handler.dispatchMessage(Handler.java:99) 
at android.os.Looper.loop(Looper.java:137) 
at android.app.ActivityThread.main(ActivityThread.java:5039) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:511) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
at dalvik.system.NativeStart.main(Native Method) 
Caused by: java.lang.NullPointerException 
at test.test.Maps.onCreate(Maps.java:23) 
at android.app.Activity.performCreate(Activity.java:5104) 
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 
... 11 more 

Answer 1

該片段尚未準備好，或者在設備上使用Google Play服務時出現問題。

從the docs（強調）：

返回
的GoogleMap的。 如果片段的視圖尚未準備好，則爲空。如果片段生命週期尚未經歷onCreateView(LayoutInflater, ViewGroup, Bundle)，則可能發生這種情況。如果Google Play服務不可用，也會發生這種情況。如果Google Play服務後來可用，並且該片段已經通過onCreateView(LayoutInflater, ViewGroup, Bundle)，再次調用此方法將初始化並返回GoogleMap。

的「地圖」演示應用程序顯示一個模式來解決這個問題，嘗試如果同時在創建和恢復需要來設置地圖：

/** 
* This shows how to create a simple activity with a map and a marker on the map. 
* <p> 
* Notice how we deal with the possibility that the Google Play services APK is not 
* installed/enabled/updated on a user's device. 
*/ 
public class BasicMapActivity extends FragmentActivity { 
    /** 
    * Note that this may be null if the Google Play services APK is not available. 
    */ 
    private GoogleMap mMap; 

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

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

    /** 
    * Sets up the map if it is possible to do so (i.e., the Google Play services APK is correctly 
    * installed) and the map has not already been instantiated.. This will ensure that we only ever 
    * call {@link #setUpMap()} once when {@link #mMap} is not null. 
    * <p> 
    * If it isn't installed {@link SupportMapFragment} (and 
    * {@link com.google.android.gms.maps.MapView MapView}) will show a prompt for the user to 
    * install/update the Google Play services APK on their device. 
    * <p> 
    * A user can return to this FragmentActivity after following the prompt and correctly 
    * installing/updating/enabling the Google Play services. Since the FragmentActivity may not have been 
    * completely destroyed during this process (it is likely that it would only be stopped or 
    * paused), {@link #onCreate(Bundle)} may not be called again so we should call this method in 
    * {@link #onResume()} to guarantee that it will be called. 
    */ 
    private void setUpMapIfNeeded() { 
     // Do a null check to confirm that we have not already instantiated the map. 
     if (mMap == null) { 
      // Try to obtain the map from the SupportMapFragment. 
      mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map)) 
        .getMap(); 
      // Check if we were successful in obtaining the map. 
      if (mMap != null) { 
       setUpMap(); 
      } 
     } 
    } 

    /** 
    * This is where we can add markers or lines, add listeners or move the camera. In this case, we 
    * just add a marker near Africa. 
    * <p> 
    * This should only be called once and when we are sure that {@link #mMap} is not null. 
    */ 
    private void setUpMap() { 
     mMap.addMarker(new MarkerOptions().position(new LatLng(0, 0)).title("Marker")); 
    } 
}