java从SQLite插入和获取真实数据类型会为连续插入获取空值吗？
我一直在想，当我在SOP（sys.out.println）上的同一个db/表中插入相同的数据（类型为Double的数组）时，为什么会出现“null（s）”，因为我没有设置任何约束
我怀疑“空”会进入我的表格，但这怎么可能呢？我第一次插入值时，它工作正常，但一旦我再次尝试插入相同的值（第二次运行我的应用程序），我会在logcat上获得SOP的输出，如下所示：
12-14 13:24:43.788: I/System.out(763): 28.0
12-14 13:24:43.788: I/System.out(763): null
12-14 13:24:43.797: I/System.out(763): The data was added successfully!
12-14 13:24:43.797: I/System.out(763): Data Totals = 2
我的数据库适配器。java看起来像这样：
package com.profourth.line;
import java.util.Random;
import 安卓.content.ContentValues;
import 安卓.content.Context;
import 安卓.database.Cursor;
import 安卓.database.SQLException;
import 安卓.database.sqlite.SQLiteDatabase;
import 安卓.database.sqlite.SQLiteOpenHelper;
import 安卓.util.Log;
public class DBAdapter {
int id = 0;
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 = 2;
private static final String DATABASE_CREATE = "create table myPROmapData (phID integer, LATS real, LONS real);";
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) {
db.execSQL(DATABASE_CREATE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
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);
}
}
// ---opens the database---
public DBAdapter open() throws SQLException {
db = DBHelper.getWritableDatabase();
return this;
}
// ---closes the database---
public void close() {
DBHelper.close();
}
// ---insert a title into the database---
public long insertQuote(/* String Quote */) {
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_PHID, 100);
initialValues.put(KEY_LAT, 28.00);
initialValues.put(KEY_LON, 72.00);
return db.insert(DATABASE_TABLE, null, initialValues);
}
public int getAllEntries() {
Cursor cursor = db.rawQuery("SELECT COUNT(LATS) FROM myPROmapData",
null);
if (cursor.moveToFirst()) {
return cursor.getInt(0);
}
return cursor.getInt(0);
}
public Double[] Populate() {
Double[] myLats;
Double[] myLons;
id = getAllEntries();
/*
* Random random = new Random(); int rand =
* random.nextInt(getAllEntries()); if(rand == 0) ++rand;
*/
Cursor cursor = db.rawQuery("SELECT LATS FROM myPROmapData", null);
/*
* if(cursor.moveToFirst()) { //return cursor.getString(0); } //return
* cursor.getString(0); return myLats;
*/
Double data[] = new Double[cursor.getCount()];
if (cursor != null) {
while (cursor.moveToNext()) {
int j = 0;
while (j < cursor.getColumnCount()) {
// data[j] = cursor.getString(j);
data[j] = cursor.getDouble(j);
j++;
}
cursor.moveToNext();
}
cursor.close();
}
return data;
}
}
我的活动看起来像：
package com.profourth.line;
import 安卓.os.Bundle;
import 安卓.app.Activity;
import 安卓.content.Context;
import 安卓.database.sqlite.SQLiteDatabase;
import 安卓.view.Menu;
import 安卓.widget.Toast;
public class MapDataController extends Activity {
DBAdapter db = new DBAdapter(this);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_map_data_controller);
/*MapDataHandler dbh = new MapDataHandler(this);
SQLiteDatabase db = dbh.getWritableDatabase();
MapDataHandler handlemydata = new MapDataHandler(null);
handlemydata.onCreate(db);
handlemydata.AddRows();
handlemydata.PopulateArr();
db.close();*/
db.open();
long id = 0;
db.insertQuote();
id = db.getAllEntries();
Double[] dta = null;
dta = db.Populate();
for(int z=0;z<(dta.length);z++)
{
System.out.println(dta[z]);
}
//Context context = getApplicationContext();
CharSequence text = "The data was added successfully!\nData Totals = " + id;
/*int duration = Toast.LENGTH_LONG;
Toast toast = Toast.makeText(context, text, duration);
toast.show();*/
System.out.println(text);
//Quote.setText("");
db.close();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_map_data_controller, menu);
return true;
}
}
非常感谢您的帮助。谢谢你的阅读
解决：
下面是我更新的Populate（）方法：
public Double[] Populate() {
Double[] myLats;
Double[] myLons;
//Double[] data = null;
id = getAllEntries();
/*
* Random random = new Random(); int rand =
* random.nextInt(getAllEntries()); if(rand == 0) ++rand;
*/
int columnIndex = 0;
Cursor cursor = db.rawQuery("SELECT LATS FROM myPROmapData", null);
/*
* if(cursor.moveToFirst()) { //return cursor.getString(0); } //return
* cursor.getString(0); return myLats;
*/
Double data[] = new Double[cursor.getCount()];
if (cursor.moveToFirst())
{
for (int i = 0; i < cursor.getCount(); i++)
{
data[i] = cursor.getDouble(columnIndex);
cursor.moveToNext();
}
}
cursor.close();
return data;
}
# 1 楼答案
代码在循环中有两个
moveToNext()调用，因此它每秒读取一次值，并将数组的最后一半留空