How to set font custom font to Spinner text programmatically?

You would apply the font through your own custom SpinnerAdapter, in getView() and getDropDownView().

Try this create custom custom_spinner.xml

<?xml version="1.0" encoding="utf-8"?>

<com.xxxx.xxxx.CheckedTextViewC

    xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@android:id/text1"
    style="?android:attr/spinnerDropDownItemStyle"
    android:singleLine="true"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:ellipsize="marquee"
    android:textAlignment="center"
    android:paddingTop="5dp"
    android:paddingBottom="5dp"
    android:textSize="18sp"

    />

Create custom CheckedtextView like this

import android.content.Context;
import android.graphics.Typeface;
import android.util.AttributeSet;
import android.widget.CheckedTextView;

public class CheckedTextViewC extends CheckedTextView {

    public CheckedTextViewC(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        // TODO Auto-generated constructor stub
    }
    public CheckedTextViewC(Context context, AttributeSet attrs) {
        super(context, attrs);
        // TODO Auto-generated constructor stub
    }
    public CheckedTextViewC(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }
    public void setTypeface(Typeface tf, int style) {
        if(!this.isInEditMode()){
        Typeface normalTypeface = Typeface.createFromAsset(getContext().getAssets(), "font/Roboto-Light.ttf");
        Typeface boldTypeface = Typeface.createFromAsset(getContext().getAssets(), "font/Roboto-Light.ttf");

        if (style == Typeface.BOLD) {
            super.setTypeface(boldTypeface/*, -1*/);
        } else {
            super.setTypeface(normalTypeface/*, -1*/);
        }
        }

    }
}

implemente the new layout

adapter= new ArrayAdapter <String>(Menu.this,R.layout.custom_spinner, list);

If you implement your Adapter in another file, you can access the "getAssets()" function from the constructor of the Adapter, as you have the Context as a parameter.

public class YourItemAdapter extends ArrayAdapter<String> {
int recurso;
Typeface tf;

public YourItemAdapter(Context _context, int _resource,
        List<String> _items) {

    super(_context, _resource, _items);
    recurso=_resource;
    tf=Typeface.createFromAsset(_context.getAssets(),"font/digital-7.ttf");
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    //You can use the new tf here.
    TextView spinner_text=(TextView)findViewById(R.id.text1);
    spinner_text.setTypeface(tf);
    }
}

This is what worked for me (using ideas both from CommonsWare's and gsanllorente's answers):

private static class MySpinnerAdapter extends ArrayAdapter<String> {
    // Initialise custom font, for example:
    Typeface font = Typeface.createFromAsset(getContext().getAssets(),
                        "fonts/Blambot.otf");

    // (In reality I used a manager which caches the Typeface objects)
    // Typeface font = FontManager.getInstance().getFont(getContext(), BLAMBOT);

    private MySpinnerAdapter(Context context, int resource, List<String> items) {
        super(context, resource, items);
    }

    // Affects default (closed) state of the spinner
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        TextView view = (TextView) super.getView(position, convertView, parent);
        view.setTypeface(font);
        return view;
    }

    // Affects opened state of the spinner
    @Override
    public View getDropDownView(int position, View convertView, ViewGroup parent) {
        TextView view = (TextView) super.getDropDownView(position, convertView, parent);
        view.setTypeface(font);
        return view;
    }
}

If you, like me, originally populated the Spinner using ArrayAdapter.createFromResource() and an array resource (as in Spinner documentation), then you'd use MySpinnerAdapter like this:

MySpinnerAdapter<String> adapter = new MySpinnerAdapter(
        getContext(),
        R.layout.view_spinner_item,
        Arrays.asList(getResources().getStringArray(R.array.my_array))
);
spinner.setAdapter(adapter);