每次我尝试在我的手机上测试我的应用程序时，它都会显示一条提示“不幸的是，该应用程序已停止”。
我已经检查了构建路径，并确保添加了 Google Play 服务库。我已经尝试搜索几个关于如何修复的线程，但它们都没有工作。所以我把这篇文章作为最后的手段让别人手动检查。
显现：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="in.wptrafficanalyzer.locationmarkersqlite"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<permission
android:name="in.wptrafficanalyzer.locationmarkersqlite.permission.MAPS_RECEIVE"
android:protectionLevel="signature"/>
<uses-permission android:name="in.wptrafficanalyzer.locationmarkersqlite.permission.MAPS_RECEIVE"/>
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES"/>
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
<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" >
<activity
android:name="in.wptrafficanalyzer.locationmarkersqlite.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>
<provider
android:name="LocationsContentProvider"
android:authorities="in.wptrafficanalyzer.locationmarkersqlite.locations"
android:exported="false" />
<meta-data
android:name="com.google.android.maps.v2.API_KEY"
android:value="YOUR_ANDROID_API_KEY" />
</application>
</manifest>
活动主要：
<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"
tools:context=".MainActivity" >
<fragment
android:id="@+id/map"
android:layout_width="match_parent"
android:layout_height="match_parent"
class="com.google.android.gms.maps.SupportMapFragment" />
</RelativeLayout>
主要活动.java：
package in.wptrafficanalyzer.locationmarkersqlite;
import android.app.Dialog;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.LoaderManager.LoaderCallbacks;
import android.support.v4.content.CursorLoader;
import android.support.v4.content.Loader;
import android.view.Menu;
import android.widget.Toast;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.GoogleMap.OnMapClickListener;
import com.google.android.gms.maps.GoogleMap.OnMapLongClickListener;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
public class MainActivity extends FragmentActivity implements LoaderCallbacks<Cursor> {
GoogleMap googleMap;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Getting Google Play availability status
int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getBaseContext());
// Showing status
if(status!=ConnectionResult.SUCCESS){ // Google Play Services are not available
int requestCode = 10;
Dialog dialog = GooglePlayServicesUtil.getErrorDialog(status, this, requestCode);
dialog.show();
}else { // Google Play Services are available
// Getting reference to the SupportMapFragment of activity_main.xml
SupportMapFragment fm = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
// Getting GoogleMap object from the fragment
googleMap = fm.getMap();
// Enabling MyLocation Layer of Google Map
googleMap.setMyLocationEnabled(true);
// Invoke LoaderCallbacks to retrieve and draw already saved locations in map
getSupportLoaderManager().initLoader(0, null, this);
}
googleMap.setOnMapClickListener(new OnMapClickListener() {
@Override
public void onMapClick(LatLng point) {
// Drawing marker on the map
drawMarker(point);
// Creating an instance of ContentValues
ContentValues contentValues = new ContentValues();
// Setting latitude in ContentValues
contentValues.put(LocationsDB.FIELD_LAT, point.latitude );
// Setting longitude in ContentValues
contentValues.put(LocationsDB.FIELD_LNG, point.longitude);
// Setting zoom in ContentValues
contentValues.put(LocationsDB.FIELD_ZOOM, googleMap.getCameraPosition().zoom);
// Creating an instance of LocationInsertTask
LocationInsertTask insertTask = new LocationInsertTask();
// Storing the latitude, longitude and zoom level to SQLite database
insertTask.execute(contentValues);
Toast.makeText(getBaseContext(), "Marker is added to the Map", Toast.LENGTH_SHORT).show();
}
});
googleMap.setOnMapLongClickListener(new OnMapLongClickListener() {
@Override
public void onMapLongClick(LatLng point) {
// Removing all markers from the Google Map
googleMap.clear();
// Creating an instance of LocationDeleteTask
LocationDeleteTask deleteTask = new LocationDeleteTask();
// Deleting all the rows from SQLite database table
deleteTask.execute();
Toast.makeText(getBaseContext(), "All markers are removed", Toast.LENGTH_LONG).show();
}
});
}
private void drawMarker(LatLng point){
// Creating an instance of MarkerOptions
MarkerOptions markerOptions = new MarkerOptions();
// Setting latitude and longitude for the marker
markerOptions.position(point);
// Adding marker on the Google Map
googleMap.addMarker(markerOptions);
}
private class LocationInsertTask extends AsyncTask<ContentValues, Void, Void>{
@Override
protected Void doInBackground(ContentValues... contentValues) {
/** Setting up values to insert the clicked location into SQLite database */
getContentResolver().insert(LocationsContentProvider.CONTENT_URI, contentValues[0]);
return null;
}
}
private class LocationDeleteTask extends AsyncTask<Void, Void, Void>{
@Override
protected Void doInBackground(Void... params) {
/** Deleting all the locations stored in SQLite database */
getContentResolver().delete(LocationsContentProvider.CONTENT_URI, null, null);
return null;
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public Loader<Cursor> onCreateLoader(int arg0,
Bundle arg1) {
// Uri to the content provider LocationsContentProvider
Uri uri = LocationsContentProvider.CONTENT_URI;
// Fetches all the rows from locations table
return new CursorLoader(this, uri, null, null, null, null);
}
@Override
public void onLoadFinished(Loader<Cursor> arg0,
Cursor arg1) {
int locationCount = 0;
double lat=0;
double lng=0;
float zoom=0;
// Number of locations available in the SQLite database table
locationCount = arg1.getCount();
// Move the current record pointer to the first row of the table
arg1.moveToFirst();
for(int i=0;i<locationCount;i++){
// Get the latitude
lat = arg1.getDouble(arg1.getColumnIndex(LocationsDB.FIELD_LAT));
// Get the longitude
lng = arg1.getDouble(arg1.getColumnIndex(LocationsDB.FIELD_LNG));
// Get the zoom level
zoom = arg1.getFloat(arg1.getColumnIndex(LocationsDB.FIELD_ZOOM));
// Creating an instance of LatLng to plot the location in Google Maps
LatLng location = new LatLng(lat, lng);
// Drawing the marker in the Google Maps
drawMarker(location);
// Traverse the pointer to the next row
arg1.moveToNext();
}
if(locationCount>0){
// Moving CameraPosition to last clicked position
googleMap.moveCamera(CameraUpdateFactory.newLatLng(new LatLng(lat,lng)));
// Setting the zoom level in the map on last position is clicked
googleMap.animateCamera(CameraUpdateFactory.zoomTo(zoom));
}
}
@Override
public void onLoaderReset(Loader<Cursor> arg0) {
// TODO Auto-generated method stub
}
}
位置数据库.java：
package in.wptrafficanalyzer.locationmarkersqlite;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class LocationsDB extends SQLiteOpenHelper{
/** Database name */
private static String DBNAME = "locationmarkersqlite";
/** Version number of the database */
private static int VERSION = 1;
/** Field 1 of the table locations, which is the primary key */
public static final String FIELD_ROW_ID = "_id";
/** Field 2 of the table locations, stores the latitude */
public static final String FIELD_LAT = "lat";
/** Field 3 of the table locations, stores the longitude*/
public static final String FIELD_LNG = "lng";
/** Field 4 of the table locations, stores the zoom level of map*/
public static final String FIELD_ZOOM = "zom";
/** A constant, stores the the table name */
private static final String DATABASE_TABLE = "locations";
/** An instance variable for SQLiteDatabase */
private SQLiteDatabase mDB;
/** Constructor */
public LocationsDB(Context context) {
super(context, DBNAME, null, VERSION);
this.mDB = getWritableDatabase();
}
/** This is a callback method, invoked when the method getReadableDatabase() / getWritableDatabase() is called
* provided the database does not exists
* */
@Override
public void onCreate(SQLiteDatabase db) {
String sql = "create table " + DATABASE_TABLE + " ( " +
FIELD_ROW_ID + " integer primary key autoincrement , " +
FIELD_LNG + " double , " +
FIELD_LAT + " double , " +
FIELD_ZOOM + " text " +
" ) ";
db.execSQL(sql);
}
/** Inserts a new location to the table locations */
public long insert(ContentValues contentValues){
long rowID = mDB.insert(DATABASE_TABLE, null, contentValues);
return rowID;
}
/** Deletes all locations from the table */
public int del(){
int cnt = mDB.delete(DATABASE_TABLE, null , null);
return cnt;
}
/** Returns all the locations from the table */
public Cursor getAllLocations(){
return mDB.query(DATABASE_TABLE, new String[] { FIELD_ROW_ID, FIELD_LAT , FIELD_LNG, FIELD_ZOOM } , null, null, null, null, null);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
LocationContenteProvider.java:
package in.wptrafficanalyzer.locationmarkersqlite;
import java.sql.SQLException;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.net.Uri;
/** A custom Content Provider to do the database operations */
public class LocationsContentProvider extends ContentProvider{
public static final String PROVIDER_NAME = "in.wptrafficanalyzer.locationmarkersqlite.locations";
/** A uri to do operations on locations table. A content provider is identified by its uri */
public static final Uri CONTENT_URI = Uri.parse("content://" + PROVIDER_NAME + "/locations" );
/** Constant to identify the requested operation */
private static final int LOCATIONS = 1;
private static final UriMatcher uriMatcher ;
static {
uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI(PROVIDER_NAME, "locations", LOCATIONS);
}
/** This content provider does the database operations by this object */
LocationsDB mLocationsDB;
/** A callback method which is invoked when the content provider is starting up */
@Override
public boolean onCreate() {
mLocationsDB = new LocationsDB(getContext());
return true;
}
/** A callback method which is invoked when insert operation is requested on this content provider */
@Override
public Uri insert(Uri uri, ContentValues values) {
long rowID = mLocationsDB.insert(values);
Uri _uri=null;
if(rowID>0){
_uri = ContentUris.withAppendedId(CONTENT_URI, rowID);
}else {
try {
throw new SQLException("Failed to insert : " + uri);
} catch (SQLException e) {
e.printStackTrace();
}
}
return _uri;
}
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
// TODO Auto-generated method stub
return 0;
}
/** A callback method which is invoked when delete operation is requested on this content provider */
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
int cnt = 0;
cnt = mLocationsDB.del();
return cnt;
}
/** A callback method which is invoked by default content uri */
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
if(uriMatcher.match(uri)==LOCATIONS){
return mLocationsDB.getAllLocations();
}
return null;
}
@Override
public String getType(Uri uri) {
return null;
}
}
日志猫：
11-06 18:13:23.327: E/AndroidRuntime(2219): FATAL EXCEPTION: main
11-06 18:13:23.327: E/AndroidRuntime(2219): java.lang.RuntimeException: Unable to start activity ComponentInfo{in.wptrafficanalyzer.locationmarkersqlite/in.wptrafficanalyzer.locationmarkersqlite.MainActivity}: java.lang.NullPointerException
11-06 18:13:23.327: E/AndroidRuntime(2219): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
11-06 18:13:23.327: E/AndroidRuntime(2219): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
11-06 18:13:23.327: E/AndroidRuntime(2219): at android.app.ActivityThread.access$600(ActivityThread.java:141)
11-06 18:13:23.327: E/AndroidRuntime(2219): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
11-06 18:13:23.327: E/AndroidRuntime(2219): at android.os.Handler.dispatchMessage(Handler.java:99)
11-06 18:13:23.327: E/AndroidRuntime(2219): at android.os.Looper.loop(Looper.java:137)
11-06 18:13:23.327: E/AndroidRuntime(2219): at android.app.ActivityThread.main(ActivityThread.java:5041)
11-06 18:13:23.327: E/AndroidRuntime(2219): at java.lang.reflect.Method.invokeNative(Native Method)
11-06 18:13:23.327: E/AndroidRuntime(2219): at java.lang.reflect.Method.invoke(Method.java:511)
11-06 18:13:23.327: E/AndroidRuntime(2219): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
11-06 18:13:23.327: E/AndroidRuntime(2219): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
11-06 18:13:23.327: E/AndroidRuntime(2219): at dalvik.system.NativeStart.main(Native Method)
11-06 18:13:23.327: E/AndroidRuntime(2219): Caused by: java.lang.NullPointerException
11-06 18:13:23.327: E/AndroidRuntime(2219): at in.wptrafficanalyzer.locationmarkersqlite.MainActivity.onCreate(MainActivity.java:60)
11-06 18:13:23.327: E/AndroidRuntime(2219): at android.app.Activity.performCreate(Activity.java:5104)
11-06 18:13:23.327: E/AndroidRuntime(2219): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
11-06 18:13:23.327: E/AndroidRuntime(2219): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)