java - Android 谷歌地图致命异常

Question

所以我正在尝试创建一个 android 应用程序，它将读取大量飞行数据并在 Google map 上用标记表示数据。

目前我无法做很多事情，我可以生成一个显示谷歌地图的应用程序，并且已经能够使用 XML 设置开始位置。

我似乎无法添加标记，它只是崩溃了。

package com.fly.plane;

import com.fly.plane.R;
import com.google.android.gms.maps.GoogleMap;

import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;


import android.os.Bundle;
import android.support.v4.app.FragmentActivity;

public class MyMapActivity extends FragmentActivity {
GoogleMap mMap;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_my_map);

// without this next line, it will work:
        mMap.addMarker(new MarkerOptions()
        .position(new LatLng(0, 0))
        .title("Hello world"));
}

}

和 XML

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >

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

</RelativeLayout>

这是错误日志:

02-10 22:31:28.433: E/AndroidRuntime(13131): FATAL EXCEPTION: main
02-10 22:31:28.433: E/AndroidRuntime(13131): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.fly.plane/com.fly.plane.MyMapActivity}: java.lang.NullPointerException
02-10 22:31:28.433: E/AndroidRuntime(13131):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2295)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at android.app.ActivityThread.access$700(ActivityThread.java:159)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at android.os.Handler.dispatchMessage(Handler.java:99)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at android.os.Looper.loop(Looper.java:137)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at android.app.ActivityThread.main(ActivityThread.java:5419)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at java.lang.reflect.Method.invokeNative(Native Method)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at java.lang.reflect.Method.invoke(Method.java:525)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1187)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at dalvik.system.NativeStart.main(Native Method)
02-10 22:31:28.433: E/AndroidRuntime(13131): Caused by: java.lang.NullPointerException
02-10 22:31:28.433: E/AndroidRuntime(13131):    at com.fly.plane.MyMapActivity.onCreate(MyMapActivity.java:21)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at android.app.Activity.performCreate(Activity.java:5372)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)
02-10 22:31:28.433: E/AndroidRuntime(13131):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2257)
02-10 22:31:28.433: E/AndroidRuntime(13131):    ... 11 more

我在 java/android 开发方面不是很擅长，所以对于导致这种情况的任何帮助将不胜感激。

问候

菲尔

Answer 1

少了一行:

mMap = ((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();

你的 onCreate() 方法必须像这样:

private GoogleMap mMap; 

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_my_map);

//Add this line.
mMap = ((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();

        mMap.addMarker(new MarkerOptions()
        .position(new LatLng(0, 0))
        .title("Hello world"));
}