我在 Android 上有一个基于 Google map 的应用程序。
简而言之，该应用程序的工作原理是:首先将一些示例数据(包含纬度/经度对的数据库)输入，读取它们，最后将它们绘制在 map 叠加层上。
当我在 Android 2.3.3 (Gingerbread) 模拟器和我的 HTC Desire S 上运行这个应用程序时，它运行良好。
但是，当我在 Android 4.0.3 (ICS) 模拟器中尝试相同的应用程序时(在对 sdk 版本的 list 文件进行更改之后)，当我尝试执行 Activity 。出现 NullPointer 异常，应用程序崩溃。
StackTrace pastebin 是 here
更新方法
public int getAllEntries() {
//int entryCount;
Cursor cursorE = db.rawQuery("SELECT COUNT(LATS) FROM myPROmapData",
null);
try {
if (cursorE.moveToFirst()) {
return cursorE.getInt(0);
}
return cursorE.getInt(0);
} finally {
cursorE.close();
}
}
--
public Double[] PopulateLats() {
//id = getAllEntries();
int LatcolumnIndex = 0;
Cursor cursor = db.rawQuery("SELECT LATS FROM myPROmapData", null);
try {
Double myLats[] = new Double[cursor.getCount()];;
if (cursor.moveToFirst()) {
for (int i = 0; i < cursor.getCount(); i++)
{
myLats[i] = cursor.getDouble(LatcolumnIndex);
cursor.moveToNext();
//cursor.close();
}
}
return myLats;
} finally {
cursor.close();
}
}
--
public Double[] PopulateLons(){
int LoncolumnIndex = 0;
Cursor cursor2 = db.rawQuery("SELECT LONS FROM myPROmapData", null);
try {
Double myLons[] = new Double[cursor2.getCount()];;
if (cursor2.moveToFirst()) {
for (int i = 0; i < cursor2.getCount(); i++)
{
myLons[i] = cursor2.getDouble(LoncolumnIndex);
cursor2.moveToNext();
//cursor.close();
}
}
return myLons;
} finally {
cursor2.close();
}
}
这是我的 Activity 代码:
public class MapMaster extends MapActivity {
/** Called when the activity is first created. */
private List mapOverlays;
private Projection projection;
private MapController mc;
private MapView mapView;
private GeoPoint gP;
// private GeoPoint gP2;
private MyOverlay myoverlay;
//Author: Kanishk
DBAdapter db = new DBAdapter(this);
public Double GetStartLat4gp()
{
Double Lat1 = null;
db.open();
//db.insertQuote(); //INSERTING SAMPLE DATA INTO TABLE
Double[] dtaStartLat = null;
dtaStartLat = db.PopulateLats();
for(int z=0;z<(dtaStartLat.length);z++)
{
//System.out.println("START_LAT:");
//System.out.println(dtaStartLat[z]);
Lat1 = dtaStartLat[z];
break;
}
db.close();
return Lat1;
}
public Double GetStartLon4gp()
{
Double Lon1 = null;
db.open();
//db.insertQuote(); //INSERTING SAMPLE DATA INTO TABLE
Double[] dtaStartLon = null;
dtaStartLon = db.PopulateLons();
for(int z=0;z<(dtaStartLon.length);z++)
{
//System.out.println("START_LAT:");
//System.out.println(dtaStartLon[z]);
Lon1 = dtaStartLon[z];
break;
}
db.close();
return Lon1;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_map_master);
//Double myStartLat = null;
//Double myStartLon = null;
mapView = (MapView) findViewById(R.id.mapview1);// Creating an instance
// of MapView
mapView.setBuiltInZoomControls(true);// Enabling the built-in Zoom
// Controls
//mapView.setTraffic(true);
//mapView.setStreetView(true);
GeoPoint gP = new GeoPoint((int)(GetStartLat4gp() * 1E6), (int)(GetStartLon4gp() * 1E6));
//gP = new GeoPoint(28570000, 77320000);// Creating a GeoPoint
System.out.println("v START CORDS v");
System.out.println(GetStartLat4gp());
System.out.println(GetStartLon4gp());
System.out.println("^ START CORDS ^");
mc = mapView.getController();
mc.setCenter(gP);
mc.setZoom(15);// Initializing the MapController and setting the map to
// center at the
// defined GeoPoint
mapOverlays = mapView.getOverlays();
projection = mapView.getProjection();
myoverlay = new MyOverlay();
mapOverlays.add(myoverlay);
db.open();
//db.CreateSampleData(); //create sample data
//db.SyncNclean(); //SYNC - CLEAN
if(db.doesDatabaseExist(this, "PROdb")){
Toast.makeText(this, "EXISTS", Toast.LENGTH_SHORT).show();
db.SyncNclean();
Toast.makeText(this, "CLEANING..CREATING SAMPLE DATA..", Toast.LENGTH_SHORT).show();
db.CreateSampleData();
Toast.makeText(this, "Sample Data Created", Toast.LENGTH_SHORT).show();
}
else{
Toast.makeText(this, "DOES NOT EXISTS", Toast.LENGTH_SHORT).show();
db.SyncNclean();
Toast.makeText(this, "CLEANING..CREATING SAMPLE DATA..", Toast.LENGTH_SHORT).show();
db.CreateSampleData();
Toast.makeText(this, "Sample Data Created", Toast.LENGTH_SHORT).show();
}
long id = 0;
id = db.getAllEntries();
CharSequence text = "The data was added successfully!\nData Totals = " + id + "Records";
System.out.println(text);
db.close();
}
public Double[] GetLats()
{
db.open();
//db.insertQuote(); //INSERTING SAMPLE DATA INTO TABLE
Double[] dtaMyLats = null;
dtaMyLats = db.PopulateLats();
for(int z=0;z<(dtaMyLats.length);z++)
{
System.out.println("LATS:");
System.out.println(dtaMyLats[z]);
}
db.close();
return dtaMyLats;
}
public Double[] GetLons()
{
db.open();
Double[] dtaMyLons = null;
dtaMyLons = db.PopulateLons();
for(int z=0;z<(dtaMyLons.length);z++)
{
System.out.println("LONS:");
System.out.println(dtaMyLons[z]);
}
db.close();
return dtaMyLons;
}
@Override
protected boolean isRouteDisplayed() {
// TODO Auto-generated method stub
return false;
}
class MyOverlay extends Overlay {
public MyOverlay() {
}
//Author: Kanishk
public void draw(Canvas canvas, MapView mapv, boolean shadow) {
super.draw(canvas, mapv, shadow);
// Configuring the paint brush
Paint mPaint = new Paint();
mPaint.setDither(true);
mPaint.setColor(Color.RED);
mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(4);
Double[] LatArr = GetLats();
Double[] LonArr = GetLons();
//generate geopoints dynamically based on coordinates from index @ array
//author: Kanishk
int count = LatArr.length;
//System.out.println(count);
for(int i=0;i<count-1;i++)
{
Double lat1;
Double lon1;
Double lat2;
Double lon2;
lat1 = LatArr[i];
lon1 = LonArr[i];
//System.out.println(LatLon[i][j]);
/*System.out.println("<< BREAK >>");
System.out.println(lat1);
System.out.println(lon1);
*/
lat2=LatArr[i+1];
//lat1 = null;
lon2=LonArr[i+1];
//lon1 = null;
//i++;
if(lat2!=null){
GeoPoint gp1 = new GeoPoint((int)(lat1 * 1E6), (int)(lon1 * 1E6)); //
GeoPoint gp2 = new GeoPoint((int)(lat2 * 1E6), (int)(lon2 * 1E6)); //
System.out.println("<< coord1 >>");
System.out.println(lat1);
System.out.println(lon1);
System.out.println("<< coord2 >>");
System.out.println(lat2);
System.out.println(lon2);
Point p11 = new Point();
Point p22 = new Point();
Path mypath = new Path();
projection.toPixels(gp1, p11);
projection.toPixels(gp2, p22);
mypath.moveTo(p22.x, p22.y);// *
mypath.lineTo(p11.x, p11.y);// *
canvas.drawPath(mypath, mPaint);
}
}
// logic end
}
}
}
DBAdapter 类:
public class DBAdapter {
int id = 0;
//public static final String KEY_ROWID = "_id";
public static final String KEY_PHID = "phID";
public String KEY_LAT = "LATS";
public String KEY_LON = "LONS";
private static final String TAG = "DBAdapter";
private static final String DATABASE_NAME = "PROdb";
private static final String DATABASE_TABLE = "myPROmapData";
private static final int DATABASE_VERSION = 9;
//private static final String DATABASE_CREATE = "create table myPROmapData (_id integer primary key autoincrement, phID integer, LATS real not null, LONS real not null);";
private static final String DATABASE_CREATE = "create table myPROmapData (phID integer, LATS real not null, LONS real not null);";
private final Context context;
private DatabaseHelper DBHelper;
private SQLiteDatabase db;
public DBAdapter(Context ctx) {
this.context = ctx;
DBHelper = new DatabaseHelper(context);
}
private static class DatabaseHelper extends SQLiteOpenHelper {
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
try {
db.execSQL(DATABASE_CREATE);
}
catch (Exception e){
Log.e(TAG,"Error: onCreate db");
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
try {
Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS myPROmapData");
onCreate(db);
}
catch (Exception e){
Log.e(TAG,"Error: onUpgrade db");
}
}
}
// ---opens the database---
public DBAdapter open() throws SQLException {
db = DBHelper.getWritableDatabase();
return this;
}
// ---closes the database---
public void close() {
DBHelper.close();
}
// ---insert sample data into the database---
public long CreateSampleData() {
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_PHID, 100);
initialValues.put(KEY_LAT, 28.4588);
initialValues.put(KEY_LON, 77.0725);
db.insert(DATABASE_TABLE, null, initialValues);
initialValues.put(KEY_LAT, 28.4719);
initialValues.put(KEY_LON, 77.0722);
db.insert(DATABASE_TABLE, null, initialValues);
/*initialValues.put(KEY_LAT, 28.5700);
initialValues.put(KEY_LON, 77.3200);*/
initialValues.put(KEY_LAT, 28.4795);
initialValues.put(KEY_LON, 77.0800);
db.insert(DATABASE_TABLE, null, initialValues);
/*initialValues.put(KEY_LAT, 28.4700);
initialValues.put(KEY_LON, 77.0300);*/
initialValues.put(KEY_LAT, 28.4813);
initialValues.put(KEY_LON, 77.0931);
db.insert(DATABASE_TABLE, null, initialValues);
/*initialValues.put(KEY_LAT, 27.1833);
initialValues.put(KEY_LON, 78.0167);*/
initialValues.put(KEY_LAT, 28.4820);
initialValues.put(KEY_LON, 77.1023);
db.insert(DATABASE_TABLE, null, initialValues);
/*initialValues.put(KEY_LAT, 26.4583);
initialValues.put(KEY_LON, 80.3173);*/
initialValues.put(KEY_LAT, 28.4804);
initialValues.put(KEY_LON, 77.1251);
return db.insert(DATABASE_TABLE, null, initialValues);
}
public int getAllEntries() {
//int entryCount;
Cursor cursorE = db.rawQuery("SELECT COUNT(LATS) FROM myPROmapData",
null);
if (cursorE.moveToFirst()) {
//entryCount = cursorE.getInt(0);
return cursorE.getInt(0);
//return entryCount;
}
// CLOSING CURSOR
cursorE.close();
return cursorE.getInt(0);
//return entryCount;
}
public boolean doesDatabaseExist(ContextWrapper context, String dbName) {
File dbFile = context.getDatabasePath(dbName);
return dbFile.exists();
}
public void SyncNclean(){
Log.w(TAG, "Sync'ing with Master Server..");
//sync master server here
Log.w(TAG, "Sync Complete..");
//Log.w(TAG, "Cleaning old data..");
db.execSQL("DROP TABLE IF EXISTS myPROmapData");
DBHelper.onCreate(db);
Log.w(TAG, "Cleaning completed..");
}
public Double[] PopulateLats() {
//id = getAllEntries();
int LatcolumnIndex = 0;
Cursor cursor = db.rawQuery("SELECT LATS FROM myPROmapData", null);
Double myLats[] = new Double[cursor.getCount()];;
if (cursor.moveToFirst())
{
for (int i = 0; i < cursor.getCount(); i++)
{
myLats[i] = cursor.getDouble(LatcolumnIndex);
cursor.moveToNext();
cursor.close();
}
}
// Original location for cursor.close()
return myLats;
}
public Double[] PopulateLons(){
int LoncolumnIndex = 0;
Cursor cursor2 = db.rawQuery("SELECT LONS FROM myPROmapData", null);
Double myLons[] = new Double[cursor2.getCount()];;
if (cursor2.moveToFirst())
{
for (int i = 0; i < cursor2.getCount(); i++)
{
myLons[i] = cursor2.getDouble(LoncolumnIndex);
cursor2.moveToNext();
cursor2.close(); //third try
}
// second tried here: cursor2.close();
}
// Original location for cursor.close()
//db.close();
return myLons;
}
}
任何帮助将不胜感激。感谢阅读。
最佳答案
空指针异常的解决方法是:
GetStartLat4gp 或 GetStartLon4gp 返回空值。
除此之外，将此方法重写为代码会更稳定
public int getAllEntries() {
//int entryCount;
Cursor cursorE = db.rawQuery("SELECT COUNT(LATS) FROM myPROmapData",
null);
try {
if (cursorE.moveToFirst()) {
return cursorE.getInt(0);
}
return cursorE.getInt(0);
} finally {
cursorE.close();
}
}
在它的原稿中，它没有关闭游标，因为它确实提前返回了。
使用 try {} finally { close resources } 作为一个好的风格，确保在任何情况下(甚至是意外异常)关闭所有资源
除此之外，将另一个游标的 close() 移回循环外，它会在循环内引发错误。 (最好也在那里使用 try/finally)
关于java - 错误 : Cursor Finalized without Prior Close，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13968129/