java - MapView 上的空指针异常

Question

我似乎无法找到以下问题的解决方案。我在尝试在 Activity 中使用以下 MapView 时遇到空指针异常。

Java

public class ActivityMAIN extends FragmentActivity implements LocationListener {

private GoogleMap mMap; 

...

mMap = ((MapFragment) getFragmentManager().findFragmentById(R.id.myMapView)).getMap();
       //LOGCAT shows Null at above statement only

LatLng sydney = new LatLng(-33.867, 151.206);

    mMap.setMyLocationEnabled(true);
    mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(sydney, 13));

    mMap.addMarker(new MarkerOptions()
            .title("Sydney")
            .snippet("The most populous city in Australia.")
            .position(sydney));

XML

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

日志猫

02-02 12:42:51.356: E/AndroidRuntime(4003): Process: com.testing.googlemaps, PID: 4003
02-02 12:42:51.356: E/AndroidRuntime(4003): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.testing.googlemaps/com.testing.googlemaps.ActivityMAIN}: java.lang.NullPointerException
02-02 12:42:51.356: E/AndroidRuntime(4003):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at android.os.Handler.dispatchMessage(Handler.java:102)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at android.os.Looper.loop(Looper.java:136)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at android.app.ActivityThread.main(ActivityThread.java:5017)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at java.lang.reflect.Method.invokeNative(Native Method)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at java.lang.reflect.Method.invoke(Method.java:515)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at dalvik.system.NativeStart.main(Native     Method)
02-02 12:42:51.356: E/AndroidRuntime(4003): Caused by: java.lang.NullPointerException
02-02 12:42:51.356: E/AndroidRuntime(4003):     at com.testing.googlemaps.ActivityMAIN.onCreate(ActivityMAIN.java:150)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at android.app.Activity.performCreate(Activity.java:5231)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
02-02 12:42:51.356: E/AndroidRuntime(4003):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)

Answer 1

问题似乎是当您调用fragment.getMap()方法时，您试图获取 Activity 创建时的 map ，此时 fragment 未显示，因此 fragment 存在但不存在GoogleMap 元素，尝试在 Activity 的 onResume() 方法上执行此操作，或者确保已使用 setContentView(...) 设置 Activity 的内容