Set custom font on an android custom textview. Untested code, be sure to test.

Static typeface

public class TextHelper{
  
  private static TypeFace typeface = null;
  
  public static void setTypeface(Context context, TextView textview){
    if(this.typeface == null){
      this.typeface = Typeface.createFromAsset(context.getAssets(), "Helvetica_Neue.ttf");
    }
    textview.setTypeface(face); 
  }
  
}


public class FontTextView extends TextView {

    public FontTextView(Context context) {
      super(context);
      TextHelper.setTypeface(context, this);
    }
    
}

Great !