Question

我正在开发一个简单的Android项目，使用一组硬编码的纬度和经度值显示折线。

MainActivity.java如下所示：包com.flip.GoogleMaps;

import android.app.Activity;
import android.app.FragmentManager;
import android.os.Bundle;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Polyline;
import com.google.android.gms.maps.model.PolylineOptions;

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    GoogleMap myMap = null;
    FragmentManager myFragmentManager = getFragmentManager();
    MapFragment myMapFragment = MapFragment)myFragmentManager.findFragmentById(R.id.map);
    myMap = myMapFragment.getMap();
    myMap.setMyLocationEnabled(true);
    myMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);
    super.onCreate(savedInstanceState);


    PolylineOptions rectOptions = new PolylineOptions()
    .add(new LatLng(37.35, -122.0))
    .add(new LatLng(37.45, -122.0))  
    .add(new LatLng(37.45, -122.2))  
    .add(new LatLng(37.35, -122.2))  
    .add(new LatLng(37.35, -122.0));

    @SuppressWarnings("unused")
    Polyline polyline = myMap.addPolyline(rectOptions);         
    }
}

activity_main.xml如下：

<LinearLayout 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"
android:orientation="vertical"
tools:context=".MainActivity" >

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

</LinearLayout>

AndroidManifest.xml如下：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.flip.GoogleMaps"
android:versionCode="1"
android:versionName="1.0" >
<uses-feature
    android:glEsVersion="0x00020000"
    android:required="true"/>
<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="17" />
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<permission      android:name="com.flip.GoogleMaps.permission.MAPS_RECEIVE"
    android:protectionLevel="signature"></permission>
<uses-permission android:name="com.flip.GoogleMaps.permission.MAPS_RECEIVE"/>
<uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES"/>


<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <meta-data
        android:name="com.google.android.maps.v2.API_KEY"
        android:value="AIzaSyBD9fsiMd_G9Pzeq2Eqas2FwJjzMGbSOnA"/>
    <uses-library android:name="com.google.android.maps" />
    <activity
        android:name="com.flip.GoogleMaps.MainActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

</application>
</manifest>

无法启动时，Logcat中会显示以下错误：

03-14 12:22:13.573: E/AndroidRuntime(1120): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.flip.GoogleMaps/com.flip.GoogleMaps.MainActivity}: java.lang.NullPointerException
03-14 12:22:13.573: E/AndroidRuntime(1120):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at android.app.ActivityThread.access$600(ActivityThread.java:130)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at android.os.Looper.loop(Looper.java:137)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at     android.app.ActivityThread.main(ActivityThread.java:4745)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at java.lang.reflect.Method.invokeNative(Native Method)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at java.lang.reflect.Method.invoke(Method.java:511)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at dalvik.system.NativeStart.main(Native Method)
03-14 12:22:13.573: E/AndroidRuntime(1120):     Caused by: java.lang.NullPointerException
03-14 12:22:13.573: E/AndroidRuntime(1120):     at com.flip.GoogleMaps.MainActivity.onCreate(MainActivity.java:20)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at android.app.Activity.performCreate(Activity.java:5008)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
03-14 12:22:13.573: E/AndroidRuntime(1120):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
03-14 12:22:13.573: E/AndroidRuntime(1120):     ... 11 more

我现在没希望了。请帮忙！

Answer 1

您的代码中存在拼写错误。变化

MapFragment myMapFragment = MapFragment)myFragmentManager.findFragmentById(R.id.map);

到

MapFragment myMapFragment = (MapFragment)myFragmentManager.findFragmentById(R.id.map);

谷歌地图折线项目显示java.lang.RuntimeException

1 个答案: