Question

我想在for循环中声明google maps标记。这是我的代码：

public void latlong() throws JSONException {

    JSONArray jsonArrayData = jsonData.getJSONArray("rows");

    for (int i = 0; i <  jsonArrayData.length(); i++) {

        JSONObject c = jsonArrayData.getJSONObject(i);

        JSONObject tmpObject = c.getJSONObject("value");
        String latString = tmpObject.getString("latitude");
        String longString = tmpObject.getString("longitude");

        double lat = Double.parseDouble(latString);
        double lng = Double.parseDouble(longString);

        System.out.println("lat: " + lat + " // long: " + lng);

       MarkerOptions place = new MarkerOptions().position(new LatLng(lat ,lng)).title("Hello Maps");
       googleMap.addMarker(place);

    }
}

我不知道为什么我会收到java.lang.NullPointerException。谢谢你的帮助！

logcat的：

02-12 01:19:02.363    9648-9648/emama.stadtrundgang E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: emama.stadtrundgang, PID: 9648
    java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.android.gms.maps.model.Marker com.google.android.gms.maps.GoogleMap.addMarker(com.google.android.gms.maps.model.MarkerOptions)' on a null object reference
            at emama.stadtrundgang.MapFragment.latlong(MapFragment.java:118)
            at emama.stadtrundgang.MapFragment.onCreateView(MapFragment.java:40)
            at android.support.v4.app.Fragment.performCreateView(Fragment.java:1786)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1126)
            at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739)
            at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1489)
            at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:486)
            at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:1073)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
            at android.support.v4.view.ViewPager$3.run(ViewPager.java:249)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
            at android.view.Choreographer.doCallbacks(Choreographer.java:580)
            at android.view.Choreographer.doFrame(Choreographer.java:549)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

Answer 1

您的地图似乎尚未初始化。为了初始化你的地图，你需要在你的onCreate（）方法中调用yourFragment.getMapAsync（），然后你会得到这样的回调：

@Override
public void onMapReady(GoogleMap map) {
    map.addMarker(new MarkerOptions()
        .position(new LatLng(10, 10))
        .title("Hello world"));
}

如果你的标记依赖于对json资源的异步调用，你可以在你的活动中设置一个标志，如下所示：

boolean isMapReady = false; boolean isDataLoaded = false;

然后在onMapReady（）和latlong（）中都可以检查标志并调用例如addMarkers（）方法。见下面的例子：

public void onMapReady(GoogleMap map) {
    isMapReady = true;
    if(isDataLoaded)
        addMarkers(map, jsonData);
}

public void latLong() {
    data = YOUR_DATA;
    isDataLoaded = true;

    if(isMapReady)
        addMarkers(map, jsonData);
}

Answer 2

当您尝试将标记放在地图上时，您的地图似乎尚未加载/初始化

尝试调用虚拟方法'com.google.android.gms.maps.model.Marker com.google.android.gms.maps.GoogleMap.addMarker（com.google.android.gms.maps.model.MarkerOptions） '在空对象参考

在for循环中创建谷歌地图标记

2 个答案: