java-在数据库上未显式调用close()

概述我需要知道在我的代码中调用db.close()的位置.我已经在onCreate()方法上添加了它,但是当我需要使用某些方法时,它说数据库未打开,然后我从onCreate()中删除了,并说未明确调用close().所以我应该在哪里关闭,它可以在类的每个方法内吗？这是代码：publicclassHoursPerDayDataHelper

我需要知道在我的代码中调用db.close()的位置.我已经在onCreate()方法上添加了它,但是当我需要使用某些方法时,它说数据库未打开,然后我从onCreate()中删除了,并说未明确调用close().所以我应该在哪里关闭,它可以在类的每个方法内吗？

这是代码：

public class HoursPerDayDataHelper {private static final String DATABASE_name = "database.db";private static final int DATABASE_VERSION = 1;protected static final String table_name = "table";protected String TAG = "HoursPerDayDataHelper";private Context context;private sqliteDatabase db;OpenHelper openHelper = null;public HoursPerDayDataHelper(Context context) {    this.context = context;    openHelper = new OpenHelper(this.context);    this.db = openHelper.getWritableDatabase();    openHelper.onCreate(db);}public voID close() {    if (openHelper != null) {        openHelper.close();    }}public voID deleteall() {    this.db.delete(table_name, null, null);}public String selectDuration(String date) {    String duration = "";    Integer value = 0;    String returnment = "";    Log.i(TAG, "date do select: " + date);                  Cursor cursor = this.db.query(table_name, new String[] { "duration" },            "date = ? ", new String[]{ date }, null, null, null);    Log.i(TAG, "cursor string " + cursor);    if (cursor.movetoFirst()) {        do {            Log.i(TAG, "dentro do if cursor");            duration = cursor.getString(0);            value += Integer.parseInt(duration);        } while (cursor.movetoNext());        returnment = Integer.toString(value);    }else{        Log.i(TAG, "bla bla bla");    }    if (cursor != null && !cursor.isClosed()) {        cursor.close();    }    return returnment;}public ArrayList<String[]> selecttopContacts() {    ArrayList<String[]> List1 = new ArrayList<String[]>();    Cursor cursor = this.db.query(table_name, null, null, null, null, null,            "duration desc");    if (cursor.movetoFirst()) {        do {            if (cursor.getString(2) != "") {                String[] data = new String[4];                data[0] = cursor.getString(2);                data[1] = cursor.getString(4);                data[2] = cursor.getString(5);                data[3] = cursor.getString(7);                List1.add(data);            } else {                String[] data = new String[3];                data[1] = cursor.getString(4);                data[2] = cursor.getString(5);                data[3] = cursor.getString(7);                List1.add(data);            }        } while (cursor.movetoNext());    }    if (cursor != null && !cursor.isClosed()) {        cursor.close();    }    return List1;}public static class OpenHelper extends sqliteOpenHelper {    OpenHelper(Context context) {        super(context, DATABASE_name, null, DATABASE_VERSION);    }    @OverrIDe    public voID onCreate(sqliteDatabase db) {        db.execsql("CREATE table IF NOT EXISTS "                + table_name                + "(ID INTEGER PRIMARY KEY autoINCREMENT, duration TIME, date DATE, current_time TIME)");    }    @OverrIDe    public voID onUpgrade(sqliteDatabase db, int oldVersion, int newVersion) {        Log.w("HoursPerDay Database",                "Upgrading database, this will drop tables and recreate.");        db.execsql("DROP table IF EXISTS " + table_name);        onCreate(db);    }}}

这是我的活动：

public class HoursPerDay extends Activity{private String LOG_TAG = "HoursPerDay";private TextVIEw mDatedisplay;public String date;private int mYear;private int mMonth;private int mDay;private int newDay;private String hpdData; private HoursPerDayDataHelper hpd;OpenHelper openHelper = new OpenHelper(HoursPerDay.this);static final int DATE_DIALOG_ID = 0;protected voID onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentVIEw(R.layout.hours_per_day);    hpd = new HoursPerDayDataHelper(this);    // capture our VIEw elements    mDatedisplay = (TextVIEw) findVIEwByID(R.ID.datedisplay);       // get the current date    final Calendar c = Calendar.getInstance();    mYear = c.get(Calendar.YEAR);    mMonth = c.get(Calendar.MONTH);    mDay = c.get(Calendar.DAY_OF_MONTH);    // display the current date (this method is below)}@OverrIDeprotected voID onDestroy() {    super.onDestroy();    if (openHelper != null) {        openHelper.close();    }    if (hpd != null) {        hpd.close();    }}// the callback received when the user "sets" the date in the dialogprivate DatePickerDialog.OnDateSetListener mDateSetListener = new DatePickerDialog.OnDateSetListener() {    public voID onDateSet(DatePicker vIEw, int year, int monthOfYear,            int dayOfMonth) {        mYear = year;        mMonth = monthOfYear;        mDay = dayOfMonth;                          setBasicContent();        hpd.close();    }};protected Dialog onCreateDialog(int ID) {    switch (ID) {    case DATE_DIALOG_ID:        return new DatePickerDialog(this,                    mDateSetListener,                    mYear, mMonth, mDay);    }    return null;}@OverrIDepublic boolean onCreateOptionsMenu(Menu menu){    MenuInflater inflater = getMenuInflater();    inflater.inflate(R.layout.hoursperdaymenu, menu);    return true;}@OverrIDepublic boolean onoptionsItemSelected(MenuItem item){    switch(item.getItemID()){    case R.ID.filter_by_day:                        showDialog(DATE_DIALOG_ID);            return true;    case R.ID.filter_by_user:        showDialog(DATE_DIALOG_ID);        return true;    default:        return super.onoptionsItemSelected(item);    }}   public voID setBasicContent() {    date = (mMonth + 1) + "/" + newDay + "/" + mYear;           hpdData = this.hpd.selectDuration(date);    mDatedisplay.setText(hpdData);    hpd.close();}}

解决方法:

我认为有两种方法：

>在onPause方法中,检查是否有完成->关.问题：如果您的应用程序被应用程序杀手杀死,则数据库保持打开状态.
>每次读取/写入(方法)时,都会打开和关闭数据库.

编辑：
好的,我知道为什么会造成这种情况.我认为您误解了sqliteOpenHelper的用法.您无需调用onCreate方法.
最好的方法是创建一个DBHelper类,并在单独的调用中使用它,比如说sqlDataHandler.
您的活动看起来不错.我改变了几件事,看看是否有帮助.我将其标记为：

这就是Helper类中的所有内容：

public static class OpenHelper extends sqliteOpenHelper { private static final String DATABASE_name = "database.db"; private static final int DATABASE_VERSION = 1; protected static final String table_name = "table"; protected String TAG = "HoursPerDayDataHelper";

只需保留它的CREATE table就可以创建/调用它(如果不存在).
我已经看到如果直接传递字符串会发生错误

 @OverrIDe public voID onCreate(sqliteDatabase db) {    String query = "CREATE table "               + table_name               + "(ID INTEGER PRIMARY KEY autoINCREMENT, duration TIME, date DATE,          current_time TIME)";    db.execsql(query);    } }@OverrIDepublic voID onUpgrade(sqliteDatabase db, int oldVersion, int newVersion) {} OpenHelper(Context context) {     super(context, DATABASE_name, null, DATABASE_VERSION); }}

要使用它：
只需调用您的DataHandler类：

OpenHelper helper = new OpenHelper(ctx);// sqliteDatabase db = helper.getReadableDatabase();sqliteDatabase db = helper.getWritableDatabase();

所有其他内容,例如删除,添加等,都应在“ DataHandler”类中完成.
只需在此处使用相同的两种方法即可获取数据库.最后,完成 *** 作后,只需在DataHandler类db.close()中进行调用.
这样,活动本身永远不会直接使用de DB.我认为更好的做法;)

希望对您有所帮助.如有其他疑问,请问:)

EDIT2：

首先,通常它应该与内部类一起工作.
但是：如果您想从另一个类中添加另一个表,它将不再起作用.这就是为什么这是从一开始就将其放在单独的类中的更好方法.它甚至可以重用(进行一些小的调整).
将我发布的代码放在您的类OpenHelper中.而已.
然后,将数据处理的东西放在一个类中：DataHandlerDB.

代码示例：

package ...;import java.util.ArrayList;import java.util.List;import androID.content.ContentValues;import androID.content.Context;import androID.database.Cursor;import androID.database.sqlite.sqliteDatabase;public class DataHandlerDB {  public static voID persistAll(Context ctx, List<Module> moduleList) {      DatabaseHelper helper = new DatabaseHelper(ctx);      sqliteDatabase db = helper.getWritableDatabase();      ContentValues values = new ContentValues();      for (Module m : moduleList) {          values.put("_ID", m.get_ID());          values.put("name", m.getModule());          db.insert("module", null, values);      }      db.close();  }  public static List<Module> findAll(Context ctx) {      List<Module> result = new ArrayList<Module>();      DatabaseHelper helper = new DatabaseHelper(ctx);      sqliteDatabase db = helper.getReadableDatabase();      Cursor c = db.query(ModuleDB.table_name, new String[] { ModuleDB.ID,            ModuleDB.MODulE}, null, null, null, null, null);      while (c.movetoNext()) {          Module m = new Module(c.getInt(0), c.getString(1));          result.add(m);      }      c.close();      db.close();      return result;  }  // Update Database entry  public static voID update(Context ctx, Module m) {      DatabaseHelper helper = new DatabaseHelper(ctx);      sqliteDatabase db = helper.getWritableDatabase();      ContentValues values = new ContentValues();      values.put("_ID", m.get_ID());      values.put("name", m.getModule());      db.update("module", values, null, null);      db.close();  }  public static voID delete(Context ctx, Module m) {      DatabaseHelper helper = new DatabaseHelper(ctx);      sqliteDatabase db = helper.getWritableDatabase();      ContentValues values = new ContentValues();      values.put("_ID", m.get_ID());      values.put("name", m.getModule());      db.delete("module","_ID = m.get_ID()", null);      db.close();  }  public static voID createDB(Context ctx) {      DatabaseHelper helper = new DatabaseHelper(ctx);      sqliteDatabase db = helper.getWritableDatabase();      db.close();  }}

为了提高效率,方法是静态的,您无需创建对象.
像这样使用它：在您的活动中

    protected voID onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);            // get the a writable DB, in case it's not existing it gets created.    DataHandlerDB.createDB(this);    // get stuff out of DB    moduleList = DataHandlerDB.findAll(this);    adapter = new ArrayAdapter<Module>(this,            androID.R.layout.simple_List_item_1, moduleList);    setlistadapter(adapter);}

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