删除中间视图时,Autolayout会折叠空间

Question

关于如何正确定义约束,在删除给定视图时会折叠视图之间的空间,我感到有点难过.我尝试添加大于或等于关系的垂直约束,但是,似乎不满足约束的最小距离.

例如,给定以下具有三个约束V的布局:[A] -5- [B],V:[B] -5- [C],并且V:[A] - (> = 5) - [C] :

[ View A ]
    |
   5 pt
    |
[ View B ]
    |
   5 pt
    |
[ View C ]

删除视图后,BI希望它看起来像这样:

[ View A ]
    |
   5 pt
    |
[ View C ]

但它看起来像这样:

[ View A ]
    |
   5 pt + 5 pt + height of view B
    |
[ View C ]

Answer 1

您可以添加V:[A] -5- [C],优先级低于1000.

[superview]
    |
[ View A ]
    |             |
   5 pt (1000)    | 
    |             |
[ View B ]       5 pt (999)
    |             |
   5 pt (1000)    |
    |             |
[ View C ]        

Answer 2

如果您正在寻找可扩展性，您可能必须用代码来完成。我用类似的东西

UIView *superView = /* whatever the superview of your views is, probably self.view in a lot of cases */
NSArray *arrViews = [NSArray arrayWithObjects:/* put only the things you want to show in here, do not put the hidden things, and put them in order from top to bottom */, nil];
CGFloat buffer = 5;

[superView addConstraint:[NSLayoutConstraint constraintWithItem:[arrViews objectAtIndex:0] attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:superView attribute:NSLayoutAttributeTop multiplier:1 constant:buffer]];
for (int i = 1; i < arrViews.count; i++)
{
     [superView addConstraint:[NSLayoutConstraint constraintWithItem:[arrViews objectAtIndex:i] attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:[arrViews objectAtIndex:i-1] attribute:NSLayoutAttributeBottom multiplier:1 constant:buffer]];
}
[superView addConstraint:[NSLayoutConstraint constraintWithItem:[arrViews lastObject] attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:superView attribute:NSLayoutAttributeBottom multiplier:1 constant:-1*(buffer)]]; 

buffer这将在顶部项目和它的超级视图之间，然后在每个子视图和它正上方的子视图之间，然后在底部视图和超级视图之间放置一个固定的间距（大小 = ）。每次从 中删除项目时都必须调用此函数arrViews，然后调用[superView needsLayout]。您还需要确保以某种方式设置高度限制，否则您会收到错误。如果所有东西都具有相同的高度，您可以在循环中添加另一行来添加高度约束。