IOS计算文字高度

NSString* str = @"你好";

　const float kFontSize = 18.f;

NSStringDrawingOptions options =  NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading;

CGRect rect = [str boundingRectWithSize:CGSizeMake(MAXFLOAT,MAXFLOAT) options:options attributes:@{NSFontAttributeName:[UIFont systemFontOfSize:kFontSize]} context:nil];

CGFloat realHeight = ceilf(rect.size.height);