ItemizedOverlay.getIndexToDraw中的NullPointerException

Question

我有一个相对简单的MapActivity,我试图在给定的地图区域内显示一个"阵营"列表.我创建了一个名为CampOverlayItem的自定义子类OverlayItem,一个名为CampsOverlay的自定义ItemizedOverlay返回CampOverlayItems,当然还有一个填充地图的MapActivity子类.

我正在使用我的活动中创建的AsyncTask从数据库中提取叠加数据.AsyncTask是从附加到MapView的ViewTreeObserver.OnGlobalLayoutListener触发的.

在AsyncTask的onPostExecute方法中,我创建了一个CampsOverlay类的新实例,并向其传递了一个从数据库返回的阵营列表(在doInBackground中获取).然后我打电话给:

mapView.getOverlays().add(newOverlay);

newOverlay是我刚刚创建的CampsOverlay.所有这些代码都运行没有错误,但是当Map尝试绘制自己时,我得到一个带有以下堆栈跟踪的NullPointerException:

java.lang.NullPointerException
   at
com.google.android.maps.ItemizedOverlay.getIndexToDraw(ItemizedOverlay.java:
211)
   at
com.google.android.maps.ItemizedOverlay.draw(ItemizedOverlay.java:240)
   at com.google.android.maps.Overlay.draw(Overlay.java:179)
   at com.google.android.maps.OverlayBundle.draw(OverlayBundle.java:
42)
   at com.google.android.maps.MapView.onDraw(MapView.java:476)
   at android.view.View.draw(View.java:6274)
   at android.view.ViewGroup.drawChild(ViewGroup.java:1526)
   at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1256)
   at android.view.ViewGroup.drawChild(ViewGroup.java:1524)
   at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1256)
   at android.view.View.draw(View.java:6277)
   at android.widget.FrameLayout.draw(FrameLayout.java:352)
   at android.view.ViewGroup.drawChild(ViewGroup.java:1526)
   at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1256)
   at android.view.ViewGroup.drawChild(ViewGroup.java:1524)
   at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1256)
   at android.view.ViewGroup.drawChild(ViewGroup.java:1524)
   at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1256)
   at android.view.ViewGroup.drawChild(ViewGroup.java:1524)
   at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1256)
   at android.view.ViewGroup.drawChild(ViewGroup.java:1524)
   at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1256)
   at android.view.View.draw(View.java:6277)
   at android.widget.FrameLayout.draw(FrameLayout.java:352)
   at android.view.ViewGroup.drawChild(ViewGroup.java:1526)
   at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1256)
   at android.view.View.draw(View.java:6277)
   at android.widget.FrameLayout.draw(FrameLayout.java:352)
   at com.android.internal.policy.impl.PhoneWindow
$DecorView.draw(PhoneWindow.java:1883)
   at android.view.ViewRoot.draw(ViewRoot.java:1332)
   at android.view.ViewRoot.performTraversals(ViewRoot.java:1097)
   at android.view.ViewRoot.handleMessage(ViewRoot.java:1613)
   at android.os.Handler.dispatchMessage(Handler.java:99)
   at android.os.Looper.loop(Looper.java:123)
   at android.app.ActivityThread.main(ActivityThread.java:4203)
   at java.lang.reflect.Method.invokeNative(Native Method)
   at java.lang.reflect.Method.invoke(Method.java:521)
   at com.android.internal.os.ZygoteInit
$MethodAndArgsCaller.run(ZygoteInit.java:791)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549)
   at dalvik.system.NativeStart.main(Native Method)

因为它似乎特别相关,这里是我的ItemizedOverlay子类的代码:

public class CampsOverlay extends ItemizedOverlay<CampOverlayItem> {
    private ArrayList<Camp> camps = null;

    public CampsOverlay(Drawable defaultMarker, ArrayList<Camp> theCamps)
{
        super(defaultMarker);
        this.camps = theCamps;
    }

    @Override
    protected CampOverlayItem createItem(int i) {
        Camp camp = camps.get(i);
        CampOverlayItem item = new CampOverlayItem(camp);
        return item;
    }

    @Override
    protected boolean onTap(int index) {
        // TODO Auto-generated method stub
        return super.onTap(index);
    }

    @Override
    public int size() {
        return camps.size();
    }

}

有谁知道这里会发生什么？我试图验证我控制的所有内容都是非空的.如有必要,我可以提供更多代码.

Answer 1

我不知道你在哪里打电话populate()给你CampsOverlay.

这是一个示例项目,显示了覆盖项的异步加载 - 如果populate()不是问题,它可能会给你一些想法.