How to use NSString drawInRect to center text?

Martins answer is pretty close, but it has a few small errors. Try this:

NSMutableParagraphStyle* style = [[NSMutableParagraphStyle alloc] init];
[style setAlignment:NSCenterTextAlignment];
NSDictionary *attr = 
  [NSDictionary dictionaryWithObject:style 
                              forKey:NSParagraphStyleAttributeName];
[myString drawInRect:someRect withAttributes:attr];
[style release];

You'll have to create a new NSMutableParagraphStyle (instead of using the default paragraph style as Martin suggested) because [NSMutableParagraphStyle defaultParagraphStyle] returns an NSParagraphStyle, which doesn't have the setAlignment method. Also, you don't need the string @"NSParagraphStyleAttributeName"—just NSParagraphStyleAttributeName.

This works for me:

    CGRect viewRect = CGRectMake(x, y, w, h);
    UIFont* font = [UIFont systemFontOfSize:15];
    CGSize size = [nsText sizeWithFont:font
                     constrainedToSize:viewRect.size
                         lineBreakMode:(UILineBreakModeWordWrap)];  
    float x_pos = (viewRect.size.width - size.width) / 2; 
    float y_pos = (viewRect.size.height - size.height) /2; 
    [someText drawAtPoint:CGPointMake(viewRect.origin.x + x_pos, viewRect.origin.y + y_pos) withFont:font];

Vertical alignment you'll have to do yourself ((height of view + height of string)/2). Horizontal alignment you can do with:

NSMutableParagraphStyle *style = [[NSParagraphStyle defaultParagraphStyle] mutableCopy];
style.alignment = NSTextAlignmentCenter;
NSDictionary *attr = [NSDictionary dictionaryWithObject:style forKey:NSParagraphStyleAttributeName];
[myString drawInRect:someRect withAttributes:attr];

This works for me for horizontal alignment

[textX drawInRect:theRect 
         withFont:font 
    lineBreakMode:UILineBreakModeClip 
        alignment:UITextAlignmentCenter];