changing font size of UIButton

I have a UIButton which displays a text, with the following code:

 [button setTitle:@"Join this group" forState:UIControlStateNormal];

however, how do I change the font size for this? I tried

button.titleLabel.font = [UIFont fontWithName:@"Arial-MT" size:8.0];

but I think it's a totally different thing. Or at least how do I make the text to adjust to the size of the button frame. Should I just use textLabel.text instead?

The reason that the code you're posting isn't working is probably because Arial isn't present in iOS. You can change the properties of a UIButton's titleLabel just like any other instance of UILabel. Read about that here.

So, you can change the font size with something like:

button.titleLabel.font = [UIFont systemFontOfSize:14.0];

You can choose a font by name, but not all fonts are available on iOS. Here's a list of ones that are.