<item name="fontFamily">@font/avalon</item>

public class MyTextView extends TextView {

public MyTextView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    init();
}

public MyTextView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
}

public MyTextView(Context context) {
    super(context);
    init();
}

private void init() {
    if (!isInEditMode()) {
        Typeface tf = Typeface.createFromAsset(getContext().getAssets(), "fonts/custom.ttf");
        setTypeface(tf);
    }
}

Typeface typeface=Typeface.createFromAsset(getAssets(), "fonts/custom.ttf");
myTextView.setTypeface(typeface);