How to set Spinner default value to null?

Alternatively, you could override your spinner adapter, and provide an empty view for position 0 in your getView method, and a view with 0dp height in the getDropDownView method.

This way, you have an initial text such as "Select an Option..." that shows up when the spinner is first loaded, but it is not an option for the user to choose (technically it is, but because the height is 0, they can't see it).

This is a complete implementation of Paul Bourdeaux's idea, namely returning a special initial view (or an empty view) in getView() for position 0.

It works for me and is relatively straightforward. You might consider this approach especially if you already have a custom adapter for your Spinner. (In my case, I was using custom adapter in order to easily customise the layout of the items, each item having a couple of TextViews.)

The adapter would be something along these lines:

public class MySpinnerAdapter extends ArrayAdapter<MyModel> {

    public MySpinnerAdapter(Context context, List<MyModel> items) {
        super(context, R.layout.my_spinner_row, items);
    }

    @Override
    public View getDropDownView(int position, View convertView, @NonNull ViewGroup parent) {
        if (position == 0) {
            return initialSelection(true);
        }
        return getCustomView(position, convertView, parent);
    }

    @NonNull
    @Override
    public View getView(int position, View convertView, @NonNull ViewGroup parent) {
        if (position == 0) {
            return initialSelection(false);
        }
        return getCustomView(position, convertView, parent);
    }


    @Override
    public int getCount() {
        return super.getCount() + 1; // Adjust for initial selection item
    }

    private View initialSelection(boolean dropdown) {
        // Just an example using a simple TextView. Create whatever default view 
        // to suit your needs, inflating a separate layout if it's cleaner.
        TextView view = new TextView(getContext());
        view.setText(R.string.select_one);
        int spacing = getContext().getResources().getDimensionPixelSize(R.dimen.spacing_smaller);
        view.setPadding(0, spacing, 0, spacing);

        if (dropdown) { // Hidden when the dropdown is opened
            view.setHeight(0);
        }

        return view;
    }

    private View getCustomView(int position, View convertView, ViewGroup parent) {
        // Distinguish "real" spinner items (that can be reused) from initial selection item
        View row = convertView != null && !(convertView instanceof TextView) 
        ? convertView :
        LayoutInflater.from(getContext()).inflate(R.layout.my_spinner_row, parent, false);

        position = position - 1; // Adjust for initial selection item
        MyModel item = getItem(position);

        // ... Resolve views & populate with data ...

        return row;
    }

}

That's it. Note that if you use a OnItemSelectedListener with your Spinner, in onItemSelected() you'd also have to adjust position to take the default item into account, for example:

if (position == 0) {
    return;
} else {
    position = position - 1;
}
MyModel selected = items.get(position);

is it possible have a spinner that loads with nothing selected

Only if there is no data. If you have 1+ items in the SpinnerAdapter, the Spinner will always have a selection.

Spinners are not designed to be command widgets. Users will not expect a selection in a Spinner to start an activity. Please consider using something else, like a ListView or GridView, instead of a Spinner.

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EDIT

BTW, I forgot to mention -- you can always put an extra entry in your adapter that represents "no selection", and make it the initial selected item in the Spinner.