問題描述

在 此技術說明中，Apple 聲明您可以通過向 UISCrollView 的超級視圖添加約束來固定/浮動 UIScrollView 的子視圖.我試過了，但我做錯了，我不知道是什么問題.

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.

請注意，您可以通過在視圖和滾動視圖的子樹之外的視圖(例如滾動視圖的超級視圖)之間創建約束，使滾動視圖的子視圖看起來浮動(不滾動)在其他滾動內容之上.

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.

這就是我所做的.我已經設置了 UIScrollView 并嘗試將固定視圖添加到滾動視圖的頂部，如下所示:

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)]];

但是，這不起作用，添加的視圖將與滾動視圖一起移動并且不會浮動".有什么想法嗎?

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

推薦答案

在視圖和滾動視圖子樹之外的視圖之間，例如滾動視圖的超級視圖.

這部分很關鍵.self.scrollView 是 _testOverlay 的超級視圖.因此，在 @"|[_testOverlay]|" 中，豎線引用 self.scrollView.你必須用 _testOverlay 和(我想)self.view 之間的約束替換這個約束.我不確定視覺格式語言是否可行，但您當然可以使用 constraintWithItem:attribute:relatedBy:toItem:attribute:multiplier:constant 來實現.它會是這樣的(我不會發布整個代碼，因為它很長):

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]];

這篇關于UIScrollView 中的固定/浮動視圖與 AutoLayout的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！