如何在android中正确关闭光标

Question

我有这个使用 sqlite 的数据库，我在关闭游标时遇到问题，它说 Application did not close the cursor or database object that was opened here 这是 logcat

10-18 08:40:56.354: E/Cursor(331): android.database.sqlite.DatabaseObjectNotClosedException: Application did not close the cursor or database object that was opened here
10-18 08:40:56.354: E/Cursor(331):  at android.database.sqlite.SQLiteCursor.<init>(SQLiteCursor.java:210)
10-18 08:40:56.354: E/Cursor(331):  at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:53)
10-18 08:40:56.354: E/Cursor(331):  at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1345)
10-18 08:40:56.354: E/Cursor(331):  at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1229)
10-18 08:40:56.354: E/Cursor(331):  at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1184)
10-18 08:40:56.354: E/Cursor(331):  at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1264)
10-18 08:40:56.354: E/Cursor(331):  at standard.internet.marketing.mymovingfriend.SQLHandler.checkMove(SQLHandler.java:1094)
10-18 08:40:56.354: E/Cursor(331):  at standard.internet.marketing.mymovingfriend.ListMovingNames$3.onKey(ListMovingNames.java:98)
10-18 08:40:56.354: E/Cursor(331):  at android.view.View.dispatchKeyEvent(View.java:3735)
10-18 08:40:56.354: E/Cursor(331):  at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:788)
10-18 08:40:56.354: E/Cursor(331):  at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:788)
10-18 08:40:56.354: E/Cursor(331):  at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:788)
10-18 08:40:56.354: E/Cursor(331):  at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:788)
10-18 08:40:56.354: E/Cursor(331):  at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchKeyEvent(PhoneWindow.java:1667)
10-18 08:40:56.354: E/Cursor(331):  at com.android.internal.policy.impl.PhoneWindow.superDispatchKeyEvent(PhoneWindow.java:1102)
10-18 08:40:56.354: E/Cursor(331):  at android.app.Activity.dispatchKeyEvent(Activity.java:2063)
10-18 08:40:56.354: E/Cursor(331):  at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1643)
10-18 08:40:56.354: E/Cursor(331):  at android.view.ViewRoot.deliverKeyEventToViewHierarchy(ViewRoot.java:2471)
10-18 08:40:56.354: E/Cursor(331):  at android.view.ViewRoot.handleFinishedEvent(ViewRoot.java:2441)
10-18 08:40:56.354: E/Cursor(331):  at android.view.ViewRoot.handleMessage(ViewRoot.java:1735)
10-18 08:40:56.354: E/Cursor(331):  at android.os.Handler.dispatchMessage(Handler.java:99)
10-18 08:40:56.354: E/Cursor(331):  at android.os.Looper.loop(Looper.java:123)
10-18 08:40:56.354: E/Cursor(331):  at android.app.ActivityThread.main(ActivityThread.java:4627)
10-18 08:40:56.354: E/Cursor(331):  at java.lang.reflect.Method.invokeNative(Native Method)
10-18 08:40:56.354: E/Cursor(331):  at java.lang.reflect.Method.invoke(Method.java:521)
10-18 08:40:56.354: E/Cursor(331):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
10-18 08:40:56.354: E/Cursor(331):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
10-18 08:40:56.354: E/Cursor(331):  at dalvik.system.NativeStart.main(Native Method)

这个问题困扰了我 3 天。

这里有一些相关代码：

public class SQLHandler {

    public static final String KEY_MOVENAME = "movename";
    public static final String KEY_ID1 = "_id";
    public static final String KEY_ID5 = "_id";
    public static final String KEY_MOVEDATE = "movedate";
    public static final String KEY_TOTALMOVEWEIGHT = "totalmoveweight";
    public static final String KEY_TOTALITEM = "totalitem";

    private static final String DATABASE_NAME = "mymovingfriend";
    private static final int DATABASE_VERSION = 1;

    public static final String KEY_LISTITEMNAME = "listitemname";
    public static final String KEY_LISTITEMWEIGHT = "listitemweight";
    public static final String KEY_LISTITEMROOM = "listitemroom";

    private static final String DATABASE_TABLE1 = "movingname";
    private static final String DATABASE_TABLE5 = "listitem";

    public static final String CREATE_TABLE_1 = "CREATE TABLE " + DATABASE_TABLE1 + " (" + 
            KEY_ID1 + " INTEGER PRIMARY KEY AUTOINCREMENT," + 
            KEY_MOVEDATE + " TEXT NOT NULL, " + 
            KEY_TOTALMOVEWEIGHT + " TEXT NOT NULL, " + 
            KEY_TOTALITEM + " INTEGER NOT NULL, " +
            KEY_MOVENAME + " TEXT NOT NULL);";

    public static final String CREATE_TABLE_2 = "CREATE TABLE " + DATABASE_TABLE2 + " (" + 
            KEY_ID2 + " INTEGER PRIMARY KEY AUTOINCREMENT," + 
            KEY_ROOMMOVEHOLDER + " TEXT NOT NULL, " + 
            KEY_ROOMWEIGHT + " TEXT NOT NULL, " + 
            KEY_ROOM + " TEXT NOT NULL);";

    public static final String CREATE_TABLE_5 = "CREATE TABLE " + DATABASE_TABLE5 + " (" + 
            KEY_ID5 + " INTEGER PRIMARY KEY AUTOINCREMENT," + 
            KEY_LISTITEMNAME + " TEXT NOT NULL, " + 
            KEY_LISTITEMWEIGHT + " TEXT NOT NULL, " +
            KEY_LISTITEMROOM + " TEXT NOT NULL);";

    private DbHelper ourHelper;
    private final Context ourContext;
    private SQLiteDatabase ourDatabase;

    private static class DbHelper extends SQLiteOpenHelper{

        public DbHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
            // TODO Auto-generated constructor stub
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            // TODO Auto-generated method stub
            db.execSQL(CREATE_TABLE_1);
            db.execSQL(CREATE_TABLE_2);
            db.execSQL(CREATE_TABLE_3);
            db.execSQL(CREATE_TABLE_4);
            db.execSQL(CREATE_TABLE_5);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldversion, int newversion) {
            // TODO Auto-generated method stub
            db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE1);
            db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE2);
            db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE3);
            db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE4);
            db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE5);
            onCreate(db);
        }
    }

    public SQLHandler(Context c){
        ourContext = c;
    }

    public SQLHandler open() throws SQLException{
        ourHelper = new DbHelper(ourContext);
        ourDatabase = ourHelper.getWritableDatabase();
        return this;
    }

    public void close(){
        ourDatabase.close();
        ourHelper.close();
    }

    public long createMove(String smovename){
        ContentValues cv = new ContentValues();
        cv.put(KEY_MOVENAME, smovename);
        cv.put(KEY_MOVEDATE, "Not yet set");
        cv.put(KEY_TOTALMOVEWEIGHT, "0");
        cv.put(KEY_TOTALITEM, 0);
        return ourDatabase.insert(DATABASE_TABLE1, null, cv);
    }

    public void createList(){

        String[] sroom = new String[]{"Kitchen", "Bedroom", "Dinning Room"};
        String[] sitem = new String[]{"Dishwasher", "Bed", "Table"};
        String[] sweight = new String[]{"40", "25", "15"};

        for (int i = 0; i < sroom.length; i++) {
            cv.put(KEY_LISTITEMROOM, sroom[i]);
            cv.put(KEY_LISTITEMNAME, sitem[i]);
            cv.put(KEY_LISTITEMWEIGHT, sweight[i]);
            ourDatabase.insert(DATABASE_TABLE5, null, cv);
        }
    }

    public void setMoveDate(String smovedate, String smovename){
        ContentValues cv = new ContentValues();
        cv.put(KEY_MOVEDATE, smovedate);
        ourDatabase.update(DATABASE_TABLE1, cv, KEY_MOVENAME + "='" + smovename + "'", null);
    }

    public void setMoveWeight(String smoveweight, String smovename){
        ContentValues cv = new ContentValues();
        cv.put(KEY_TOTALMOVEWEIGHT, smoveweight);
        ourDatabase.update(DATABASE_TABLE1, cv, KEY_MOVENAME + "='" + smovename + "'", null);
    }

    public void setTotalItem(String smovename, int imoveitem){
        ContentValues cv = new ContentValues();
        cv.put(KEY_TOTALITEM, imoveitem);
        ourDatabase.update(DATABASE_TABLE1, cv, KEY_MOVENAME + "='" + smovename + "'", null);
    }

    public void renameRoom(String movename, String roomname, String currentroom){
        ContentValues cv = new ContentValues();
        cv.put(KEY_ROOM, roomname);
        ourDatabase.update(DATABASE_TABLE2, cv, KEY_ROOMMOVEHOLDER + "='" + movename + "'" + " AND " + KEY_ROOM + "='" + currentroom + "'", null);
    }

    public void setRoomWeight(String sroomweight, String smovename, String sroomname){
        ContentValues cv = new ContentValues();
        cv.put(KEY_ROOMWEIGHT, sroomweight);
        ourDatabase.update(DATABASE_TABLE2, cv, KEY_ROOMMOVEHOLDER + "='" + smovename + "'" + " AND " + KEY_ROOM + "='" + sroomname + "'", null);
    }

    public long addRooms(String sroommoveholder, String sroom){
        ContentValues cv = new ContentValues();
        cv.put(KEY_ROOMMOVEHOLDER, sroommoveholder);
        cv.put(KEY_ROOM, sroom);
        cv.put(KEY_ROOMWEIGHT, "0");
        return ourDatabase.insert(DATABASE_TABLE2, null, cv);
    }

    public long addNewItems(String sitemmoveholder, String sroomholder, String sitemname, String sitemvalue, String sitemweight){
        ContentValues cv = new ContentValues();
        cv.put(KEY_ITEMMOVEHOLDER, sitemmoveholder);
        cv.put(KEY_ROOMHOLDER, sroomholder);
        cv.put(KEY_ITEMNAME, sitemname);
        cv.put(KEY_ITEMVALUE, sitemvalue);
        cv.put(KEY_ITEMWEIGHT, sitemweight);
        return ourDatabase.insert(DATABASE_TABLE3, null, cv);
    }

    public void updateItems(String sitemmoveholder, String sroomholder, String sitemname, String sitemvalue, String sitemweight){
        ContentValues cv = new ContentValues();
        cv.put(KEY_ITEMVALUE, sitemvalue);
        cv.put(KEY_ITEMWEIGHT, sitemweight);
        ourDatabase.update(DATABASE_TABLE3, cv, KEY_ITEMMOVEHOLDER + "='" + sitemmoveholder + "'" + " AND " + 
                KEY_ROOMHOLDER + "='" + sroomholder + "'" + " AND " + KEY_ITEMNAME + "='" + sitemname + "'", null);
    }

    public Cursor getMove(){
        String[] columns = new String[]{KEY_ID1, KEY_MOVENAME};

        Cursor c = null;
        try {
            c = ourDatabase.query(DATABASE_TABLE1, columns, null, null, null, null, null);
        } catch (Exception e) {
            c.close();
        }
        return c;
    }

    public String getTotalWeight(String m) throws SQLException{
        String[] columns = new String[]{KEY_ID1, KEY_MOVENAME, KEY_MOVEDATE, KEY_TOTALMOVEWEIGHT};

        Cursor c = null;
        try {
            c = ourDatabase.query(DATABASE_TABLE1, columns, KEY_MOVENAME + "= '" + m + "'", null, null, null, null);
            if (c != null) {
                c.moveToFirst();
                String totalWeight = c.getString(3);
                return totalWeight;
            }
        } catch (Exception e) {
            c.close();
        }
        return null;

    }

    public String getTotalWeightLBS(String m) throws SQLException{
        String[] columns = new String[]{KEY_ID1, KEY_MOVENAME, KEY_MOVEDATE, KEY_TOTALMOVEWEIGHT};

        Cursor c = null;
        try {
            c = ourDatabase.query(DATABASE_TABLE1, columns, KEY_MOVENAME + "= '" + m + "'", null, null, null, null);
            if (c != null) {
                c.moveToFirst();
                int x = Integer.parseInt(c.getString(3)) * 7;
                String totalWeight = "" + x + " lbs";
                return totalWeight;
            }
        } catch (Exception e) {
            c.close();
        }
        return null;

    }

    public String getDateMove(String md){
        String[] columns = new String[]{KEY_ID1, KEY_MOVENAME, KEY_MOVEDATE};

        Cursor c = null;try {
            c = ourDatabase.query(DATABASE_TABLE1, columns, KEY_MOVENAME + "= '" + md + "'", null, null, null, null);

            if (c != null) {
                c.moveToFirst();
                String moveDate = c.getString(2);
                return moveDate;
            }
        } catch (Exception e) {
            c.close();
        }
        return null;
    }

    public ArrayList<String> loadRooms(String mn) throws SQLException{
        String[] columns = new String[]{KEY_ID2, KEY_ROOMMOVEHOLDER, KEY_ROOM};

        ArrayList<String> array = new ArrayList<String>();

        Cursor c = null;
        try {
            c = ourDatabase.query(DATABASE_TABLE2, columns,KEY_ROOMMOVEHOLDER + "='" + mn + "'", 
                    null, null, null, null);
            int iroom = c.getColumnIndex(KEY_ROOM);

            for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
                array.add(c.getString(iroom));
            }
        } catch (Exception e) {
            c.close();
        }
        return array;
    }

    public void deleteMove(String m) throws SQLException{
        ourDatabase.delete(DATABASE_TABLE1, KEY_MOVENAME + "='" + m + "'", null);
        ourDatabase.delete(DATABASE_TABLE2, KEY_ROOMMOVEHOLDER + "='" + m + "'", null);
        ourDatabase.delete(DATABASE_TABLE3, KEY_ITEMMOVEHOLDER + "='" + m + "'", null);
        ourDatabase.delete(DATABASE_TABLE4, KEY_TODOMOVE + "='" + m + "'", null);
    }

    public ArrayList<String> getitems(){
        String[] columns = new String[]{KEY_ID5, KEY_ITEMNAME};
        ArrayList<String> items;
        items = new ArrayList<String>();

        Cursor c = null;
        try {
            c = ourDatabase.query(DATABASE_TABLE5, columns, null, null, null, null, null);

            for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
                items.add(c.getString(1));
            }
        } catch (Exception e) {
            c.close();
        }

        return items;
    }

    public ArrayList<String> getitemweight(){
        String[] columns = new String[]{KEY_ID5, KEY_ITEMWEIGHT};
        ArrayList<String> items = new ArrayList<String>();

        Cursor c = null;
        try {
            c = ourDatabase.query(DATABASE_TABLE5, columns, null, null, null, null, null);
            for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
                items.add(c.getString(1));
            }
        } catch (Exception e) {
            c.close();
        }

        return items;
    }

    public ArrayList<String> getitemclass(){
        String[] columns = new String[]{KEY_ID5, KEY_LISTITEMROOM};
        ArrayList<String> items = new ArrayList<String>();

        Cursor c = null;
        try {
            c = ourDatabase.query(DATABASE_TABLE5, columns, null, null, null, null, null);

            for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
                items.add(c.getString(1));
            }
        } catch (Exception e) {
            c.close();
        }

        return items;
    }

}

Answer 1

getDateMove、getTotalWeightLBS、loadRooms、...中没有关闭光标。

在不再需要光标的地方关闭它。在这些方法中使用try-finally，即使抛出异常，也会保证在finally块中执行代码。

从这里更改方法中的代码：

try{
  // get data from cursor
} catch (Exception e) {
    c.close();
}

到这里：

try {
   // get data from cursor
} catch (Exception e) {
   // exception handling
} finally {
   if(c != null){
       c.close();
   }
} 

Answer 2

如果一个元素正在实现 AutoCloseable（就像 Cursor.class 所做的那样），我建议执行 try-with-resources，就像描述的 here 一样。 如果你使用 Retrolambda，它有 try-with-resources 向后移植。

所以你的代码：

Cursor cursor = db.query("tableName", columns, null, null, null, null, null);
try {
    if (cursor.moveToFirst()) return cursor.getString(3);
    else return null;
} finally {
   cursor.close();
}

只会变成：

try (Cursor cursor = db.query("tableName", columns, null, null, null, null, null)) {
    if (cursor.moveToFirst()) return cursor.getString(3);
    else return null;
}

Answer 3

在finally 中关闭光标将保证它会被关闭；

public void myfunc() {

    Cursor c = null;

    try {

      c = ... // Open cursor here
      return .... // maybe return something

    } finally {
       if(c != null) { c.close(); }
    } 
}

Answer 4

如果您使用 Kotlin（也可以在 Java 中以稍微不同的方式使用）和 Android 4.1 及更高版本，您可以使用这个：

    cursor?.use { 
       //..do stuff
    }

例如，您可以查看here。

如果您想使用 Java，请执行以下操作：

        try (Cursor cursor = ...) {
            // do something
        }

Answer 5

在onStop() 或onDestroy() 活动的方法中关闭您的数据库！

Answer 6

您正在尝试使用

关闭 catch 块内的光标

catch (Exception e) {
            c.close();
        }

但是如果你没有得到任何异常，那么它将如何关闭

所以把它放在 finally 块中

finally {
            c.close();
        }

Answer 7

试试这个，

在onStop() 或onDestroy()

检查光标是否为空

@Override
public void onStop(){
 Cursor cursor;

 if(cursor!=null){
  cursor.close();}
 }

如果没有则关闭光标。

编辑

关闭数据库对象

DatabaseObject db;
if(db!=null)
{ db.close();}

希望对你有帮助。