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我对Android开发非常陌生，所以我确信这会变成我错过的一些愚蠢的东西，但我有两个活动：StartScreen和Map。 StartScreen只是简单的文本和一个按钮，它应该会带您进入地图活动。无法实例化ComponentInfo NullPointerException
我已经尝试将Map活动减少到几乎没有，并且我确定它没有导致错误，但我无法弄清楚是什么。
这是错误的logcat的输出，当我按下按钮连接两个活动发生了：
04-28 20:40:24.097: E/AndroidRuntime(13458): FATAL EXCEPTION: main
04-28 20:40:24.097: E/AndroidRuntime(13458): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.rr.freespace/com.rr.freespace.Map}: java.lang.NullPointerException
04-28 20:40:24.097: E/AndroidRuntime(13458): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
04-28 20:40:24.097: E/AndroidRuntime(13458): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2229)
04-28 20:40:24.097: E/AndroidRuntime(13458): at android.app.ActivityThread.access$600(ActivityThread.java:139)
04-28 20:40:24.097: E/AndroidRuntime(13458): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1261)
04-28 20:40:24.097: E/AndroidRuntime(13458): at android.os.Handler.dispatchMessage(Handler.java:99)
04-28 20:40:24.097: E/AndroidRuntime(13458): at android.os.Looper.loop(Looper.java:154)
04-28 20:40:24.097: E/AndroidRuntime(13458): at android.app.ActivityThread.main(ActivityThread.java:4945)
04-28 20:40:24.097: E/AndroidRuntime(13458): at java.lang.reflect.Method.invokeNative(Native Method)
04-28 20:40:24.097: E/AndroidRuntime(13458): at java.lang.reflect.Method.invoke(Method.java:511)
04-28 20:40:24.097: E/AndroidRuntime(13458): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
04-28 20:40:24.097: E/AndroidRuntime(13458): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
04-28 20:40:24.097: E/AndroidRuntime(13458): at dalvik.system.NativeStart.main(Native Method)
04-28 20:40:24.097: E/AndroidRuntime(13458): Caused by: java.lang.NullPointerException
04-28 20:40:24.097: E/AndroidRuntime(13458): at android.content.ContextWrapper.getPackageName(ContextWrapper.java:127)
04-28 20:40:24.097: E/AndroidRuntime(13458): at android.content.ComponentName.<init>(ComponentName.java:75)
04-28 20:40:24.097: E/AndroidRuntime(13458): at android.content.Intent.<init>(Intent.java:3475)
04-28 20:40:24.097: E/AndroidRuntime(13458): at com.rr.freespace.Map.<init>(Map.java:12)
04-28 20:40:24.097: E/AndroidRuntime(13458): at java.lang.Class.newInstanceImpl(Native Method)
04-28 20:40:24.097: E/AndroidRuntime(13458): at java.lang.Class.newInstance(Class.java:1319)
04-28 20:40:24.097: E/AndroidRuntime(13458): at android.app.Instrumentation.newActivity(Instrumentation.java:1039)
04-28 20:40:24.097: E/AndroidRuntime(13458): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2101)
这里是我的StartScreen.java：
package com.rr.freespace;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
public class StartScreen extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_start_screen);
}
public void doIt(View view) { // Do something in response to button }
Intent intent = new Intent(this, Map.class);
startActivity(intent);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.start_screen, menu);
return true;
}
}
的activity_start_screen.xml布局文件：
<RelativeLayout 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:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".StartScreen" >
<TextView
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_marginTop="180dp"
android:text="@string/hometext2"
android:textAppearance="?android:attr/textAppearanceLarge" />
<Button
android:id="@+id/button1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:layout_centerVertical="true"
android:layout_margin="20dp"
android:text="@string/doit"
android:onClick="doIt" />
</RelativeLayout>
最后，清单文件：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.rr.freespace"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="11"
android:targetSdkVersion="17" />
<permission
android:name="com.example.mapdemo.permission.MAPS_RECEIVE"
android:protectionLevel="signature"/>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="com.rr.freespace.permission.MAPS_RECEIVE"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES"/>
<uses-feature
android:glEsVersion="0x00020000"
android:required="true"/>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme">
<uses-library android:name="com.google.android.maps" />
<meta-data
android:name="com.google.android.maps.v2.API_KEY"
android:value="AIzaSyBaoeVjdRY312vJ5KMLXxmzpKHhPiYqASo"/>
<activity
android:name="com.rr.freespace.StartScreen"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.rr.freespace.Map"
android:label="@string/app_name" >
</activity>
</application>
</manifest>
我希望有人能弄清楚这里发生了什么，因为我不能！干杯!
编辑：这里的map.java码，有可能是在这里更多的错误，我没有到呢，因为我昨天一起砍死大部分在此之前我曾访问Android设备：
package com.rr.freespace;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.provider.Settings;
import android.view.Menu;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.GoogleMapOptions;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.model.LatLng;
public class Map extends Activity {
final Context context = this;
Intent goback = new Intent(this, StartScreen.class);
protected LocationManager locationManager;
protected LocationListener listener;
private GoogleMap mMap;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_map);
LocationManager locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
final boolean gpsEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
if (!gpsEnabled) {
AlertDialog.Builder gpssettings = new AlertDialog.Builder(context);
gpssettings.setMessage(R.string.gpstext)
.setTitle(R.string.gpstitle);
gpssettings.setPositiveButton(R.string.gpsok, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
// User clicked OK button
enableLocationSettings();
}
});
gpssettings.setNegativeButton(R.string.gpscancel, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
// User cancelled the dialog
startActivity(goback);
}
});
}
mMap = ((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();
GoogleMapOptions options = new GoogleMapOptions();
options.mapType(GoogleMap.MAP_TYPE_NORMAL)
.compassEnabled(false)
.rotateGesturesEnabled(false)
.tiltGesturesEnabled(false);
//Get GPS data
final LocationListener listener = new LocationListener() {
@Override
public void onLocationChanged(Location location) {
// A new location update is received. Do something useful with it. Update the UI with
// the location update.
final LatLng position = new LatLng(location.getLatitude(),location.getLongitude());
mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(position, 15));
}
@Override
public void onProviderDisabled(String provider) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
};
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER,
1000, // 10-second interval.
5, // 5 meters.
listener);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.map, menu);
return true;
}
private void enableLocationSettings() {
Intent settingsIntent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
startActivity(settingsIntent);
}
protected void onStop() {
super.onStop();
locationManager.removeUpdates(listener);
}
}
邮政编码Map.java – Gustek 2013-04-28 20:21:02