NullPointerException异常，而试图折线/标记添加到的GoogleMap [英] NullPointerException whilst trying to add polyline/marker to a GoogleMap
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问题描述
我有一个GoogleMap对象（这是我使用的是GoogleMapOptions已经操作了）一个SupportMapFragment，它会显示/运行正常，直到我打电话的GetMap（）。addPolyline（...），我得到一个NullPointerException异常。
I have a SupportMapFragment with a GoogleMap object (which I have manipulated already using a GoogleMapOptions) and it is displaying/functioning fine, until I call getMap().addPolyline(...) where I get a NullPointerException.
下面是我对活动布局的xml：
Here is my layout xml for the Activity:
<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" >
<TextView
android:id="@+id/tripSummary"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:text="@string/trip_summary"
tools:context=".Start" />
<TextView
android:id="@+id/tripDetails"
android:layout_below="@id/tripSummary"
android:layout_alignParentLeft="true"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:text="@string/awaiting_location"
tools:context=".Start" />
<fragment
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:map="http://schemas.android.com/apk/res-auto"
android:id="@+id/map"
android:layout_below="@id/tripDetails"
android:layout_width="match_parent"
android:layout_height="match_parent"
map:cameraZoom="13"
android:name="com.google.android.gms.maps.SupportMapFragment" />
</RelativeLayout>
下面是我在活动中的createMap方法（它扩展android.support.v4.app.FragmentActivity），这就是所谓的onCreate（...）
Here is the createMap method in my Activity (which extends android.support.v4.app.FragmentActivity) which is called in onCreate(...)
private void createMap(List<LatLng> latLngs) {
float zoom = 13;
PolylineOptions poly = new PolylineOptions()
.color(Color.RED);
MarkerOptions startMarker = new MarkerOptions()
.position(latLngs.get(0))
.title("Start");
MarkerOptions endMarker = new MarkerOptions()
.position(latLngs.get(latLngs.size() - 1))
.title("End");
LatLng startLatLng = latLngs.get(0);
GoogleMapOptions mapOptions = new GoogleMapOptions();
CameraPosition cameraP = new CameraPosition(startLatLng, zoom, 0, 0);
if (mMap == null) {
// instantiate map
mMapFragment = SupportMapFragment.newInstance(mapOptions);
FragmentTransaction fragmentTransaction = getSupportFragmentManager()
.beginTransaction();
fragmentTransaction.add(R.id.map, mMapFragment);
fragmentTransaction.commit();
Log.d("Map", "fragment transaction complete");
mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map)).getMap();
// check it has been instantiated
if (mMapFragment != null) {
mapOptions.mapType(GoogleMap.MAP_TYPE_SATELLITE)
.camera(cameraP)
.compassEnabled(true);
//Add LatLngs to a polyline
for(LatLng latLng : latLngs){
poly.add(latLng);
}
mMapFragment.getMap().addPolyline(poly);
mMapFragment.getMap().addMarker(startMarker);
mMapFragment.getMap().addMarker(endMarker);
}
}
}
LogCat中：
LogCat:
01-03 20:42:42.737: E/AndroidRuntime(18116): FATAL EXCEPTION: main
01-03 20:42:42.737: E/AndroidRuntime(18116): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.project.locationapp/com.project.locationapp.TripSummary}: java.lang.NullPointerException
01-03 20:42:42.737: E/AndroidRuntime(18116): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1659)
01-03 20:42:42.737: E/AndroidRuntime(18116): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1675)
01-03 20:42:42.737: E/AndroidRuntime(18116): at android.app.ActivityThread.access$1500(ActivityThread.java:121)
01-03 20:42:42.737: E/AndroidRuntime(18116): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:943)
01-03 20:42:42.737: E/AndroidRuntime(18116): at android.os.Handler.dispatchMessage(Handler.java:99)
01-03 20:42:42.737: E/AndroidRuntime(18116): at android.os.Looper.loop(Looper.java:130)
01-03 20:42:42.737: E/AndroidRuntime(18116): at android.app.ActivityThread.main(ActivityThread.java:3701)
01-03 20:42:42.737: E/AndroidRuntime(18116): at java.lang.reflect.Method.invokeNative(Native Method)
01-03 20:42:42.737: E/AndroidRuntime(18116): at java.lang.reflect.Method.invoke(Method.java:507)
01-03 20:42:42.737: E/AndroidRuntime(18116): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
01-03 20:42:42.737: E/AndroidRuntime(18116): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:624)
01-03 20:42:42.737: E/AndroidRuntime(18116): at dalvik.system.NativeStart.main(Native Method)
01-03 20:42:42.737: E/AndroidRuntime(18116): Caused by: java.lang.NullPointerException
01-03 20:42:42.737: E/AndroidRuntime(18116): at com.project.locationapp.TripSummary.createMap(TripSummary.java:113)
01-03 20:42:42.737: E/AndroidRuntime(18116): at com.project.locationapp.TripSummary.onCreate(TripSummary.java:38)
01-03 20:42:42.737: E/AndroidRuntime(18116): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-03 20:42:42.737: E/AndroidRuntime(18116): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1623)
01-03 20:42:42.737: E/AndroidRuntime(18116): ... 11 more
我已经测试了用于获取经纬度值的数据源，并检索值的罚款。任何建议，为什么我收到一个 NullPointerException异常试图从地图时的 SupportMapFragment ？
先谢谢了。
版
推荐答案
如果您添加的 SupportMapFragment 应用于布局文件您不必手动创建一个新的实例。你只需要通过调用获得参考
If you add the SupportMapFragment to the layout file you don't have to create a new instance manually. You just need to obtain the reference by calling
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
GoogleMap map = mapFragment.getMap();
您很可能得到NPE，因为新实例片段还没有创建GoogleMap对象呢。
You are probably getting the NPE because the newly instantiated fragment haven't created the GoogleMap object yet.
这篇关于NullPointerException异常，而试图折线/标记添加到的GoogleMap的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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