Null Pointer exception when attempting to update row of sqlite database in android

Question

First off, I have looked at all the similar questions that hours of google and SO searches have displayed. No luck.

I have a Database Helper class called PropertiesDatabase which extends SQLiteOpenHelper as follows:

private static final class PropertiesDatabase extends SQLiteOpenHelper{

            static final int DATABASE_VERSION = 1;
    private static final String KEY_PROPERTIES_TABLE = "PropertiesTable";
    static final String KEY_ID = "_id";
    static final String KEY_NAME = "name";   
    static final String KEY_SIZE = "size";    
    static final String KEY_PASSWORD = "password";      

    static final String [] columnsProperties = new String[] { KEY_NAME, 
        KEY_SIZE, KEY_PASSWORD};

    private static String CREATE_TABLE;

    public PropertiesDatabase(Context context) {
        super(context, KEY_PROPERTIES_TABLE, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        CREATE_TABLE = "create table " 
                + KEY_PROPERTIES_TABLE + "(" 
                + KEY_ID + " integer primary key autoincrement, " 
                + KEY_NAME + " text not null, "  
                + KEY_SIZE + " integer," 
                + KEY_PASSWORD + " text" + ");";
        db.execSQL(CREATE_TABLE);
    }

            public void changeName(String oldName, String newName){
        SQLiteDatabase db = this.getReadableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_NAME, newName);

        db.update(KEY_PROPERTIES_TABLE, values, KEY_NAME + "=?",
                new String[] {oldName});
        db.close();
    }

            public void changeSize(String name, int n){
        SQLiteDatabase db = this.getReadableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_SIZE, n);

        db.update(KEY_PROPERTIES_TABLE, values, KEY_NAME + "=?", 
                          new String[] {name});
        db.close();
    }
}

There are many more methods in the class, but I've included changeName and changeSize because they are almost identical, but the first works and the second throws a null pointer exception. The logcat says that the call

db.update(KEY_PROPERTIES_TABLE, values, KEY_NAME + "=?", new String[] {name});

In the changeSize() method is the culprit. I checked using db.isOpen() immediately before that call, and the database is not open. It is open, however, before the update call in changeName().

I can't understand why one method works fine and the other doesn't. Any help solving that mystery would be appreciated.

Thank you for taking the time to read this.

Edit:

Here is the relevant logcat info:

01-31 13:37:17.315: E/AndroidRuntime(1978): FATAL EXCEPTION: main
01-31 13:37:17.315: E/AndroidRuntime(1978): java.lang.NullPointerException
01-31 13:37:17.315: E/AndroidRuntime(1978):     at          
android.database.sqlite.SQLiteStatement.releaseAndUnlock(SQLiteStatement.java:290)
01-31 13:37:17.315: E/AndroidRuntime(1978):     at   
android.database.sqlite.SQLiteStatement.executeInsert(SQLiteStatement.java:115)
01-31 13:37:17.315: E/AndroidRuntime(1978):     at   
android.database.sqlite.SQLiteDatabase.insertWithOnConflict(SQLiteDatabase.java:1825)
01-31 13:37:17.315: E/AndroidRuntime(1978):     at  
android.database.sqlite.SQLiteDatabase.replace(SQLiteDatabase.java:1744)
01-31 13:37:17.315: E/AndroidRuntime(1978):     at   
com.LN.AppName.DatabaseHandler$PropertiesDatabase.changeSize(DatabaseHandler.java:767)

Line 767 is, of course, the call to update.

Thanks again!

Put a breakpoint on that line. Run your code until it hits the breakpoint. Inspect all of the objects. Which one is null? — Simon
– Simon, Commented Jan 31, 2013 at 18:24
At the breakpoint the variables were this, db, values, name, and n, none of which were null. I don't think that I have some null variables, I believe the issue is that db is not open, for some reason. — Rookatu
– Rookatu, Commented Jan 31, 2013 at 19:02

Georgy Gobozov · Accepted Answer · 2013-01-31 18:24:23Z

1

I think problem is that your class is static, as I know only nested class may be static. Try to use standart method to work with database, smth like this

answered Jan 31, 2013 at 18:24

Georgy Gobozov

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4 Comments

Rookatu Over a year ago

This class actually is nested. In any case, why does this work for changeName() and not changeSize()? That is the real mystery. There is also a method called changePassword() which is almost identical and works as well.

Georgy Gobozov Over a year ago

Do you call your methods in same sequence? If yes, try to change it, try to rebulid project, try to use debugger, try do not close db after first call.

Rookatu Over a year ago

I have called the methods in different order, cleaned project and used debugger. Not closing db after the first call did not solve the problem either.

Rookatu Over a year ago

I rewrote my database code to more closely resemble the code in the link you sent. I still don't know why my original code wasn't working, but I'll move on before I've pulled all my hair out! Thanks!

Wolfram Rittmeyer · Accepted Answer · 2013-02-01 13:25:14Z

1

First off: Do not use getReadableDatabase() when you want to write to the database - and updates are writes. Use getWritableDatabase() instead. Most often this causes no problem, but it can!

Also you normally should hold onto one instance of SQLiteDatabase within your code. See this comment in SQLiteOpenHelper's code:

// Darn! The user closed the database by calling mDatabase.close().

Create one writable SQLiteDatabase object when you first use the SQLiteOpenHelper and use it within all your methods. Take care of your cursors and close the database only, when you are truely done with your database related code.

answered Feb 1, 2013 at 13:25

Wolfram Rittmeyer

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1 Comment

Rookatu Over a year ago

Actually, following Georgy Gobozov's suggestion to rewrite my database code in the way described by the link he provided, I have made those changes. This seems to have solved the problem (if not the mystery), but I'll accept his answer on that account. Thanks for the help though!

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