在UIScrollView的固定/浮动观点与自动版式 [英] Fixed / Float view in UIScrollView with AutoLayout

问题描述

在本技术说明苹果公司指出，你可以的UIScrollView的子视图固定通过添加约束UIScrollView的上海华/浮动。我想，但我做错了什么，我想不出什么问题。

  

请注意，您可以滚动视图的子视图出现通过创建视图和滚动视图的子树外的视图，如滚动视图的上海华之间的约束浮动（不滚动）比其他滚动内容。

这就是我所做的。我有一个UIScrollView已经建立并尝试将固定视图中添加像下面的滚动视图的顶部：

_testOverlay = [[UIView的页头]初始化];
_testOverlay.backgroundColor =的UIColor blueColor]
_testOverlay.translatesAutoresizingMaskIntoConstraints = NO;
[self.scrollView addSubview：_testOverlay];[self.view addConstraints：[NSLayoutConstraint constraintsWithVisualFormat：@| [_testOverlay] |选项​​：0的指标：无意见：NSDictionaryOfVariableBindings（_testOverlay）];
[self.view addConstraints：[NSLayoutConstraint constraintsWithVisualFormat：@V：| [_testOverlay（64）〕 - （大于= 0） - |选项​​：0的指标：无意见：NSDictionaryOfVariableBindings（_testOverlay）];


然而，这不工作，所添加的视图将沿着与滚动视图移动并且不会浮动。任何想法什么错在这里？

解决方案

  

视图和滚动视图的子树之外的视图，如间
  滚动视图的上海华

这部分是至关重要的。 self.scrollView 是 _testOverlay 的上海华。所以，在 @| [_testOverlay] |竖线参考 self.scrollView 。您有 _testOverlay 键，（我想）之间的约束，以取代此约束 self.view 。我不知道是否有可能与视觉格式语言，但你肯定可以使用做constraintWithItem：属性：relatedBy：toItem：属性：事半功倍：恒。它会是这样的（我不会张贴整个code，因为它是looong）：

  [self.view addConstraint：[NSLayoutConstraint
                          constraintWithItem：self.view
                          属性：NSLayoutAttributeLeft
                          relatedBy：NSLayoutRelationEqual
                          toItem：_testOverlay
                          属性：NSLayoutAttributeLeft
                          事半功倍：1.0
                          常数：0]];
 

In this technical Note Apple states that you can make a subview of UIScrollView fixed / floating by adding constraints to UISCrollView's superview. I tried that but I'm doing something wrong and I can't figure out whats the problem.

Note that you can make a subview of the scroll view appear to float (not scroll) over the other scrolling content by creating constraints between the view and a view outside the scroll view’s subtree, such as the scroll view’s superview.

That's what I did. I have a UIScrollView already set up and try to add the fixed view to the top of the scrollview like the following:

_testOverlay = [[UIView alloc] init];
_testOverlay.backgroundColor = [UIColor blueColor];
_testOverlay.translatesAutoresizingMaskIntoConstraints = NO;
[self.scrollView addSubview:_testOverlay];

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|[_testOverlay]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_testOverlay)]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[_testOverlay(64)]-(>=0)-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_testOverlay)]];

However, this does not work, the added view will move along with the scrollview and does not 'float'. Any ideas whats wrong here?

解决方案

between the view and a view outside the scroll view’s subtree, such as the scroll view’s superview.

This part is critical. self.scrollView is a superview of _testOverlay. So, in @"|[_testOverlay]|" vertical bars reference self.scrollView. You have to replace this constraint with the constraint between _testOverlay and (I suppose) self.view. I'm not sure if it's possible with the visual format language, but you certainly can do it with constraintWithItem:attribute:relatedBy:toItem:attribute:multiplier:constant. It would go like this (I won't post the whole code, because it's looong):

[self.view addConstraint:[NSLayoutConstraint
                          constraintWithItem:self.view
                          attribute:NSLayoutAttributeLeft
                          relatedBy:NSLayoutRelationEqual
                          toItem:_testOverlay
                          attribute:NSLayoutAttributeLeft
                          multiplier:1.0
                          constant:0]];

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