UITextView文本与底部对齐

Question

我正在创建UIScrollView并设置 attributedText 。出于某种原因，文本没有显示......直到我实际向下滚动。看来文字正与UIScrollView的底部对齐，我不明白为什么？！

NSString *description = NSLocalizedString(@"forgot.description", nil);
NSMutableAttributedString *paragraph = [[NSMutableAttributedString alloc] initWithString:description attributes:@{}];

NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle alloc] init];
[paragraphStyle setLineSpacing:4];
[paragraph addAttribute:NSParagraphStyleAttributeName value:paragraphStyle range:NSMakeRange(0, [paragraph length])];
[paragraph addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:12] range:NSMakeRange(0, [paragraph length])];
[paragraph addAttribute:NSForegroundColorAttributeName value:[UIColor colorWithRed:43/255.0f green:47/255.0f blue:61/255.0f alpha:1.0f] range:NSMakeRange(0, [paragraph length])];
_descriptionTextView = [[UITextView alloc] init];
_descriptionTextView.backgroundColor = [UIColor whiteColor];
_descriptionTextView.attributedText = paragraph;
_descriptionTextView.userInteractionEnabled = NO;
_descriptionTextView.scrollEnabled = NO;
_descriptionTextView.clipsToBounds = NO;

CGFloat const ComponentWidth = 280.0;
CGFloat const ComponentHeight = 40.0;
self.descriptionTextView.frame = CGRectIntegral(CGRectMake(x, y, ComponentWidth, ComponentHeight));
[self.view addSubview:self.descriptionTextView];

我认为当我将它设置为不隐藏

时，这与navigationBar有关

- (void)viewWillAppear:(BOOL)animated
{
    [self.navigationController setNavigationBarHidden:NO animated:NO];
    [super viewWillAppear:animated];
}