iOS - 純AutoLayout和UIScrollView不滾動

Question

這是我第一次使用UIScrollViews純粹的Autolayout方法。這是視圖層次結構的樣子

view 
-scrollview 
--view1 
--view2 
--view3 

scrollview應該按順序包含view1 | view2 | view3。

我將scrollviews的寬度，高度，centerx和底部空間設置爲superview。創建的view1，view2和view3都在其updateConstraints方法中設置了寬度和高度約束。此外，代碼中提供了一些限制。這個scrollview不是從左到右滾動的原因是什麼？從字面上看，我可以在網上找到關於以自動佈局以編程方式創建和添加子視圖到UIScrollView的所有指南。我發現一些提到必須爲每個視圖提供四個不同的約束，前導，尾隨，頂部和底部作爲子視圖添加到滾動視圖。這些是唯一可以指定的NSLayoutAttributes嗎？屬性如NSLayoutAttribueLeft或NSLayoutAttribueRight如何相關？我也閱讀過蘋果網站上的文檔，特別是https://developer.apple.com/library/ios/technotes/tn2154/_index.html。我附加了我目前擁有的設置。一切都是通過代碼完成的。

- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
    self.dataSource = @[ [[PCCGenericRating alloc] initWithTitle:@"Easiness" 
                 andMessage:@"WHAT A JOKERRRR" 
                andVariatons:@[ @"very easy", @"easy", @"moderate", @"hard", @"very hard"]], 

         [[PCCGenericRating alloc] initWithTitle:@"Joker" 
                 andMessage:@"WHAT A JOKERRRR" 
                andVariatons:@[ @"very easy", @"easy", @"moderate", @"hard", @"very hard"]], 

         [[PCCGenericRating alloc] initWithTitle:@"Difficulty" 
                 andMessage:@"YOu are not difficult at all" 
                andVariatons:@[ @"very easy", @"easy", @"moderate", @"hard", @"very hard"]] 
         ]; 
    [self initView]; 
} 

- (void)initView { 
    CGFloat navigationBarHeight = self.navigationController.navigationBar.frame.size.height; 
    CGFloat statusBarHeight = [[UIApplication sharedApplication] statusBarFrame].size.height; 

    CGFloat heightDifference = navigationBarHeight + statusBarHeight; 

    self.scrollView = [[UIScrollView alloc] init]; 
    self.scrollView.delegate = self; 
    [self.scrollView setTranslatesAutoresizingMaskIntoConstraints:NO]; 
    self.scrollView.backgroundColor = [UIColor greenColor]; 
    [self.view addSubview:self.scrollView]; 


    //setup constraints 
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.scrollView attribute:NSLayoutAttributeWidth 
                        relatedBy:NSLayoutRelationEqual 
                         toItem:self.view 
                        attribute:NSLayoutAttributeWidth 
                        multiplier:1.0f 
                        constant:0.0f]]; 

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.scrollView attribute:NSLayoutAttributeHeight 
                  relatedBy:NSLayoutRelationEqual 
                  toItem:self.view 
                  attribute:NSLayoutAttributeHeight 
                 multiplier:1.0f 
                  constant:-heightDifference]]; 

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.scrollView attribute:NSLayoutAttributeCenterX 
                        relatedBy:NSLayoutRelationEqual 
                         toItem:self.view 
                        attribute:NSLayoutAttributeCenterX 
                        multiplier:1.0f 
                        constant:0.0f]]; 

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.scrollView attribute:NSLayoutAttributeBottom 
                  relatedBy:NSLayoutRelationEqual 
                  toItem:self.view 
                  attribute:NSLayoutAttributeBottom 
                 multiplier:1.0f 
                  constant:0.0]]; 

    [self.dataSource enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) { 
     PCCGenericRating *rating = (PCCGenericRating *)obj; 
     PCCGenericRatingView *ratingView = [self createViewWithRating:rating]; 
     [self.scrollView addSubview:ratingView]; 

     int multiplier = (idx == 0) ? 1 : (int) (idx + 1) ; 
     [self.scrollView addConstraint:[NSLayoutConstraint constraintWithItem:ratingView 
                     attribute:NSLayoutAttributeCenterX 
                     relatedBy:NSLayoutRelationEqual 
                      toItem:self.scrollView 
                     attribute:NSLayoutAttributeCenterX 
                     multiplier:multiplier 
                     constant:0.0f]]; 

     [self.scrollView addConstraint:[NSLayoutConstraint constraintWithItem:ratingView 
                    attribute:NSLayoutAttributeCenterY 
                    relatedBy:NSLayoutRelationEqual 
                     toItem:self.scrollView 
                    attribute:NSLayoutAttributeCenterY 
                    multiplier:1.0f 
                    constant:0.0f]]; 
    }]; 
} 

- (PCCGenericRatingView *)createViewWithRating:(PCCGenericRating *)rating { 
    PCCGenericRatingView *view = [PCCGenericRatingView genericRatingViewWithTitle:rating.title andMessage:rating.message]; 
    return view; 
} 

在打印出了滾動的限制，他們看起來還好我：

po self.scrollView.constraints 
<__NSArrayM 0x115b051f0>(
<NSLayoutConstraint:0x1145d9290 PCCGenericRatingView:0x114579880.centerX == UIScrollView:0x11458d4b0.centerX>, 
<NSLayoutConstraint:0x1145d9410 PCCGenericRatingView:0x114579880.centerY == UIScrollView:0x11458d4b0.centerY>, 
<NSLayoutConstraint:0x1145d9dd0 PCCGenericRatingView:0x1145d9560.centerX == 2*UIScrollView:0x11458d4b0.centerX>, 
<NSLayoutConstraint:0x1145d9e40 PCCGenericRatingView:0x1145d9560.centerY == UIScrollView:0x11458d4b0.centerY>, 
<NSLayoutConstraint:0x1145da6b0 PCCGenericRatingView:0x1145d9e90.centerX == 3*UIScrollView:0x11458d4b0.centerX>, 
<NSLayoutConstraint:0x1145da730 PCCGenericRatingView:0x1145d9e90.centerY == UIScrollView:0x11458d4b0.centerY> 
) 

這裏是什麼樣子的截圖：

我覺得很奇怪，最後數據源中的元素是第一個顯示在滾動視圖中的視圖控制器，它應該是最後一個視圖。它也不會從左到右滾動。

Answer 1

無論您在何處打印您的約束，請嘗試打印scrollview.contentSize，它可能會是0,0，這就是您的問題所在。據我所知，正如你在文章中提到的那樣，你必須明確地將scrollview的子視圖設置爲滾動視圖左上和右下限制。設置這些會自動設置滾動視圖的contentSize，使其能夠滾動。它看起來像你只設置centerX和centerY約束，它不會將scrollviews contentSize設置爲你所需要的。

嘗試編程設置這些（這是僞代碼，但你的想法）：

• view1.topConstraint = scrollView.topConstraint
• view1.leftConstraint = scrollView.leftConstraint
• view3.bottomConstraint =滾動視圖.bottomConstraint
• view3.rightConstraint = scrollView.rightConstraint

如果您將所有這些設置正確，您的滾動視圖將正確滾動。請記住檢查內容，如果contentsize是0,0，那麼您的約束沒有正確設置。

Answer 2

確保您top_constraint爲廠景和bottom_constraint爲VIEW3會按您的滾動視圖的約束。否則滾動查看的contentSize: {0, 0}。