attr.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="RobotoTextView">
        <attr name="font" format="string" />
    </declare-styleable>
</resources>

RobotoTextView.java

public class RobotoTextView extends TextView {

    public static final String ANDROID_SCHEMA = "http://schemas.android.com/apk/res/android";

    private static HashMap<String, Typeface> fontCache = new HashMap<>();

    public RobotoTextView(Context context, AttributeSet attrs) {
        super(context, attrs);

        applyCustomFont(context, attrs);
    }

    public RobotoTextView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        applyCustomFont(context, attrs);
    }

    private void applyCustomFont(Context context, AttributeSet attrs) {
        TypedArray attributeArray = context.obtainStyledAttributes(
                attrs,
                R.styleable.RobotoTextView);

        String fontName = attributeArray.getString(R.styleable.RobotoTextView_font);
        int textStyle = attrs.getAttributeIntValue(ANDROID_SCHEMA, "textStyle", Typeface.NORMAL);

        Typeface customFont = selectTypeface(context, fontName, textStyle);
        setTypeface(customFont);

        attributeArray.recycle();
    }

    private Typeface selectTypeface(Context context, String fontName, int textStyle) {
        if (fontName.contentEquals(context.getString(R.string.roboto))) {
            return getTypeface("fonts/roboto.ttf", context);
        } else if (fontName.contentEquals(context.getString(R.string.roboto_condensed))) {
            return getTypeface("fonts/robotocondensed.ttf", context);
        } else {
            // no matching font found
            // return null so Android just uses the standard font (Roboto)
            return null;
        }
    }

    public static Typeface getTypeface(String fontname, Context context) {
        Typeface typeface = fontCache.get(fontname);

        if (typeface == null) {
            try {
                typeface = Typeface.createFromAsset(context.getAssets(), fontname);
            } catch (Exception e) {
                return null;
            }

            fontCache.put(fontname, typeface);
        }

        return typeface;
    }
}

strings.xml

<resources>
    <string name="roboto">roboto</string>
    <string name="roboto_condensed">robotocondensed</string>
</resources>