Android Drop a SQLite table

Question

I'm building an app where I've to create multiple tables on a SQLite database.

The best example I can give is of one store that I'll have to manage, so I'm creating one table for each category (wines, beers, milk, etc...) of products where I have to manage the brands that I'm selling but, if I quit from selling one of this categories I would like to be able to drop this category table.

But I tried many examples from the web and nothing works. I'm always getting the same error.

Because I've many items on my tables I built a custom list view and a custom adapter and both are working perfectly, I can delete or add new items without problems, build new tables, but the same approach doesn't work to drop my built tables.

I intentionally let my database opened until my activity is destroyed so I don't have to open it trough my adapter.

Maybe someone can help me how to drop a table with the name passed from a String, using one button or in this case, would be really helpful using my adapter button, because my idea is to add buttons on my list view.

Just to make clear, I can drop the tables if I create one editText to type my tables names and use a button to run this code:

dataBase.execSQL("DROP TABLE IF EXISTS '" + tableName + "'");

or if I run this code during the execution of the method onCreate and I give a name from a table that really exists.

dataBase.execSQL("DROP TABLE IF EXISTS 'test 1'");

So my question is not how to handle NullPointerException but how to manipulate my SQLite database from my custom adapter.

Thank you!

this is my adapter code:

public class MyCustomAdapter extends BaseAdapter implements ListAdapter {
private ArrayList<String> list = new ArrayList<String>();
private Context context;
private SQLiteDatabase dataBase;
private String tableName;

public MyCustomAdapter(ArrayList<String> list, Context context) {
    this.list = list;
    this.context = context;
}

@Override
public int getCount() {
    return list.size();
}

@Override
public Object getItem(int pos) {
    return list.get(pos);
}

@Override
public long getItemId(int pos) {
    //return list.get(pos).getId();

    //just return 0 if your list items do not have an Id variable.
    return 0;
}

@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    View view = convertView;
    if (view == null) {
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        view = inflater.inflate(R.layout.list_item_clickable, null);
    }

    //Handle TextView and display string from your list
    TextView listItemText = (TextView)view.findViewById(R.id.list_item_textview);
    listItemText.setText(list.get(position));

    //Handle buttons and add onClickListeners
    Button deleteBtn = (Button)view.findViewById(R.id.delete_btn);

    deleteBtn.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v) {

            //criar alertDialog
            AlertDialog.Builder  dialog = new AlertDialog.Builder(context);

            dialog.setTitle("Delete!");

            dialog.setMessage("Do you wish to delete this ToDo list?");

            dialog.setCancelable(false);

            dialog.setIcon(android.R.drawable.ic_delete);

            dialog.setNegativeButton("No", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialogInterface, int i) {
                    Toast.makeText(context, "No!", Toast.LENGTH_SHORT).show();
                }
            });

            dialog.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialogInterface, int i) { 
                    final String tableName= list.get( position ).toString();

                    try {

                        dataBase.execSQL("DROP TABLE IF EXISTS '" + tableName + "'");
                                //dataBase.execSQL("DROP TABLE IF EXISTS 'test 1'");

                                list.remove(position); //or some other task

                                    Toast.makeText(context, "Tabela " + tableName + " removida com sucesso!", Toast.LENGTH_SHORT).show();
                                    notifyDataSetChanged();


                    } catch (Exception e) {
                        e.printStackTrace();
                    }

                }
            });

            dialog.create();
            dialog.show();

        }
    });

    listItemText.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            //Toast.makeText(context, "Item position is: " + list.get(position), Toast.LENGTH_SHORT).show();

            Intent intent = new Intent(context, MainActivity.class);
            String tabelaNome = list.get( position ).toString();

            intent.putExtra("tableName", tableName);

           context.startActivity(intent);
        }
    });

    return view;
}

Error message

Answer 1

Note the difference between your two SQL statements:

dataBase.execSQL("DROP TABLE IF EXISTS '" + tableName + "'");
dataBase.execSQL("DROP TABLE IF EXISTS teste 1"); 

The one you say works does not have quotes around the table name.