Question

I am expanding my application with a neat “delete all”-function in my Preferences.
What i want from it? Just to, drop the table, delete all inputs… But no… It just gives me an NPE.

And now, i am really clueless…

Prefs.java

    Preference wipeDatabase = findPreference("wipeDatabase");
wipeDatabase.setOnPreferenceClickListener(new OnPreferenceClickListener() {

    public boolean onPreferenceClick(Preference arg0) {

        AlertDialog.Builder builder = new AlertDialog.Builder(Prefs.this);
        builder.setMessage("YOU SURE!??!")
        .setCancelable(false)
        .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int id) {

                    mDbHelper.deleteAll(); // <-- This is the function.

                }
        })
        .setNegativeButton("No", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int id) {
                dialog.cancel();
            }
        });
        builder.show();
        return false;

    }
});

And the function explained in databasehelper.

    public void deleteAll() {
    SQLiteDatabase dB = mDbHelper.getWritableDatabase();
    dB.execSQL("DROP TABLE "+DATABASE_TABLE);
}

But, it throws an NPE…
I’ve also tried with:

dB.delete(DATABASE_TABLE,null,null);

But with same result… What am i doing WRONG!? 🙁

SOLUTION

Prefs.java

mDbHelper.deleteDatabase(getBaseContext()); // <-- i used this.

DatabaseHelper.java

public boolean deleteDatabase(Context context) {
    return context.deleteDatabase(DATABASE_NAME);
}

Worked perfectly! Thanks!

Answer 1

Why not deleting the database instead?
It will be recreated next time you open it.

public boolean deleteDatabase(Context context) {
    return context.deleteDatabase(DATABASE_NAME);
}

It will return false if, for whatever reason, it couldn’t delete it.