Android Studio Null Pointer exception with item lists

Question

This code is very vital to my project. It refreshes items from a sql server that I have created. It does not load any of the items and gives me a Null Pointer Exception.

private void refreshItemsToInventoryList() {

    // Get the items that weren't marked as completed and add them in the
    // adapter

    AsyncTask<Void, Void, Void> task = new AsyncTask<Void, Void, Void>(){
        @Override
        protected Void doInBackground(Void... params) {

            try {
                final List<Item> results = refreshItemsFromInventoryTable();

                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        mInventoryAdapter.clear();

                        for (Item item : results) {
                            mInventoryAdapter.add(item);
                        }
                    }
                });
            } catch (final Exception e){
                Log.e("Error: ", e.getMessage());
            }

            return null;
        }
    };

    runAsyncTask(task);
}

/**
 * Refresh the list with the items in the Inventory Table
 */

@Nullable
private List<Item> refreshItemsFromInventoryTable() throws ExecutionException, InterruptedException {

    ResultSet rs;
    List<Item> inventoryItems = null;
    try {
        String query = "SELECT * FROM Inventory; ";
        Statement stmt = con.createStatement();
        rs = stmt.executeQuery(query);

        while (rs.next()){
            inventoryItems.add(new Item(rs.getString("ItemDescription")));
        }
    }
    catch (SQLException sql)
    {
        createAndShowDialog(sql.getMessage(), "Error");
    }

    return inventoryItems;
}

This code is to create and add items to a list, but it unfortunately gives me a Null Pointer Exception.

Please add Log of NPE here. Just saying it gives you a NPE doesn't help — Napster, Feb 08 '18 at 18:36

score 0 · Answer 1 · answered Feb 08 '18 at 18:32

0

Do you have records in the Inventory table? If no you will always have null as you are returning the initialized inventoryItems result

answered Feb 08 '18 at 18:32

Matthew Odedoyin

86
9

I do have an item in the Inventory Table – Darren Feb 09 '18 at 18:43

score 0 · Answer 2 · answered Feb 08 '18 at 18:34

0

First things: does your inventory database table have rows? Did you open up your database connection properly?

Whenever I get a Null Pointer Exception, I find it really helpful to set a breakpoint right before the line that the logcat points to that is in error. You can then watch the variables and items, and see if they are being populated, or are null.

answered Feb 08 '18 at 18:34

shagberg

2,427
1
12
23

Database connection is opened properly and the table does have rows. – Darren Feb 09 '18 at 18:43

Android Studio Null Pointer exception with item lists

2 Answers2