这是NSString分类(NSString (NSExtendedStringDrawing))中的一个方法:
- (CGRect)boundingRectWithSize:(CGSize)size options:(NSStringDrawingOptions)options attributes:(nullable NSDictionary<NSString *, id> *)attributes context:(nullable NSStringDrawingContext *)context NS_AVAILABLE(10_11, 7_0);
利用该方法可获取想得到的值.
CGRect textRect = [_msgStr boundingRectWithSize:CGSizeMake(contentWidth, MAXFLOAT) options:NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading attributes:@{NSFontAttributeName : [UIFont systemFontOfSize:contentFont]} context:nil];