UILabeltext动态获取宽度

   //昵称
    UIButton *nickBut = [UIButton buttonWithType:UIButtonTypeCustom];
    nickBut.userInteractionEnabled = YES;
    [nickBut setFrame:CGRectMake(0, 0, 100, 30)];
    [nickBut addTarget:self action:@selector(selectGroup) forControlEvents:UIControlEventTouchUpInside];
    [nickBut setTitle:@"勇敢的心" forState:UIControlStateNormal];
    navItem.titleView = nickBut;
   
    CGSize fontSize =[nickBut.titleLabel.text sizeWithFont:[UIFont  systemFontOfSize:16] 
                                       forWidth:120
                                  lineBreakMode:UILineBreakModeTailTruncation];
   
    nickBut.frame = CGRectMake(0, 0, fontSize.width + 16, fontSize.height);

根据UIButton的title，和字体，动态获取UIButton的宽度