Swift
//System Font
textView.font = UIFont.systemFont(ofSize: 12)
//Font of your choosing
textView.font = UIFont(name: "Font Name", size: 12)
Objective-C
//System Font
textView.font = [UIFont systemFontOfSize:12];
//Font of your choosing
textView.font = [UIFont fontWithName:@"Font Name" size:12];