当我按下按钮ListView活动以返回MapViewActivity时，我收到了以下错误。
我真的不知道出了什么问题，因为它没有显示我的代码中错误的位置。
任何建议都将不胜感激！
07-20 15:49:51.558: E/AndroidRuntime(2794): FATAL EXCEPTION: main
07-20 15:49:51.558: E/AndroidRuntime(2794): java.lang.NullPointerException
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.SurfaceView.updateWindow(SurfaceView.java:497)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.SurfaceView.updateWindow(SurfaceView.java:408)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.SurfaceView.dispatchDraw(SurfaceView.java:352)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.ViewGroup.drawChild(ViewGroup.java:1644)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.ViewGroup.drawChild(ViewGroup.java:1644)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.View.draw(View.java:6936)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.widget.FrameLayout.draw(FrameLayout.java:357)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.ViewGroup.drawChild(ViewGroup.java:1646)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.ViewGroup.drawChild(ViewGroup.java:1644)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.View.draw(View.java:6936)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.widget.FrameLayout.draw(FrameLayout.java:357)
07-20 15:49:51.558: E/AndroidRuntime(2794): at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1926)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.ViewRoot.draw(ViewRoot.java:1527)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.ViewRoot.performTraversals(ViewRoot.java:1263)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.view.ViewRoot.handleMessage(ViewRoot.java:1865)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.os.Handler.dispatchMessage(Handler.java:99)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.os.Looper.loop(Looper.java:130)
07-20 15:49:51.558: E/AndroidRuntime(2794): at android.app.ActivityThread.main(ActivityThread.java:3687)
07-20 15:49:51.558: E/AndroidRuntime(2794): at java.lang.reflect.Method.invokeNative(Native Method)
07-20 15:49:51.558: E/AndroidRuntime(2794): at java.lang.reflect.Method.invoke(Method.java:507)
07-20 15:49:51.558: E/AndroidRuntime(2794): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:847)
07-20 15:49:51.558: E/AndroidRuntime(2794): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)
07-20 15:49:51.558: E/AndroidRuntime(2794): at dalvik.system.NativeStart.main(Native Method)