如何在AutoLayout(iOS6)中使用UIScrollView？

Question

我正在尝试构建一个将具有多个不同控件的视图,但我希望视图仅在垂直方向上滚动.我正在使用自动布局,所以我不想手动指定大小(我知道我可以这样做,但据我所知,根据UIScrollView你不应该发布的说明).

因此,如果我创建一个简单的视图控制器(没有.xib文件)并简单地将以下内容添加到init方法中,我希望我的标签会换行(他们这样做)并且我的视图会垂直滚动,但是,这不是案子:

- (id)init {
    self = [super init];
    if (self) {

        UIScrollView *_scrollView = [UIScrollView new];
        [_scrollView setTranslatesAutoresizingMaskIntoConstraints:NO];

        UILabel *label1 = [UILabel new];
        UILabel *label2 = [UILabel new];

        [label1 setTranslatesAutoresizingMaskIntoConstraints:NO];
        [label2 setTranslatesAutoresizingMaskIntoConstraints:NO];

        [label1 setNumberOfLines:0];
        [label2 setNumberOfLines:0];

        [label1 setPreferredMaxLayoutWidth:240];
        [label2 setPreferredMaxLayoutWidth:240];

        NSString *sampleText = @"Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.";
        [label1 setText:sampleText];
        [label2 setText:sampleText];

        [self.view addSubview:_scrollView];
        [_scrollView addSubview:label1];
        [_scrollView addSubview:label2];

        NSArray *constraints;
        constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[_scrollView]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_scrollView)];
        [self.view addConstraints:constraints];

        constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[_scrollView]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_scrollView)];
        [self.view addConstraints:constraints];

        constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[label1]-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(label1)];
        [_scrollView addConstraints:constraints];

        constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[label2]-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(label2)];
        [_scrollView addConstraints:constraints];

        constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-[label1]-[label2]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(label1, label2)];
        [_scrollView addConstraints:constraints];
    }

    return self;
}

我认为这个代码有几个结果很奇怪.如果你在viewDidLayoutSubviews方法中记录scrollviewheight (在超级调用之后),这是应该应用所有约束的地方,那么高度报告为0.还有一个奇怪的是宽度报告的数字与我预期的不同.我期望它报告超级视图的宽度由于第一个约束(我甚至试图强制该约束内的宽度具有所谓的优先级,但它仍然不起作用).

据我了解,其UIScrollView内容大小应根据其内容的内在大小来设定,但似乎并未发生.

那么,有谁知道缺少什么？

Answer 1

我联系了Apple的支持,以便回答我的问题.代码的问题在于UIScrollView中包含的对象必须固定在垂直顶部和底部,以确定其内在内容大小.所以下面的代码行

constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-[label1]-[label2]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(label1, label2)];
[_scrollView addConstraints:constraints];

应改为:

constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-[label1]-[label2]-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(label1, label2)];
[_scrollView addConstraints:constraints];

他们还指出我在几个对象上使用"new"关键字,其中基本的"init"不是指定的初始化程序.虽然这与我的具体问题无关,但他们确实指出你应该避免这样做,因为你的对象可能处于无效状态.