根据内容的UITextView高度在iOS 9中是错误的

我通过编程动态地将视图添加到具有布局约束的scrollview中.对于文本视图组件,我想根据textview中设置的文本设置高度约束,所以我创建了扩展UITextView的类.在文本视图类中,我编写了以下代码来添加高度约束.

#import "CETextView.h"

@implementation CETextView

- (void)layoutSubviews
{
    [super layoutSubviews];

    if (!self.heightConsTraint)
    {
        self.heightConsTraint =  [NSLayoutConsTraint consTraintWithItem:self attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:100];
        [self addConsTraint:self.heightconstraint];
    }
    CGRect lRect = [self contentSizeRect];

    CGSize descriptionSize = lRect.size;
    self.heightConsTraint.constant = descriptionSize.height;

}

- (CGRect)contentSizeRect
{
    NSTextContainer* textContainer = [self textContainer];
    NSLayoutManager* layoutManager = [self layoutManager];
    [layoutManager ensureLayoutForTextContainer: textContainer];
    CGRect lRect = CGRectMake(0,320,500);
    lRect.size = self.contentSize;
    lRect.size.height = lRect.size.height + 5;
    return lRect;
}


@end

此代码在iOS 8.0中提供了正确的高度,但在iOS 9.0中提供了错误的高度.我查了苹果doc for iOS 9.0的新版本,还有一些与自动布局有关的变化.

任何帮助表示赞赏.