ios - 顶部固定有 SupplementaryView 的 JSQMessagesViewController
<p><p>
我已经覆盖了 collectionView:viewForSupplementaryElementOfKind:atIndexPath: 以快速显示我的 JSQMessagesViewController 子类的标题 View 。这确实很好用，但标题 View 会随着聊天滚动，我希望将其固定在顶部。</p>
<p>Apple 在 iOS 9 中引入了 sectionHeadersPinToVisibleBounds 属性，这应该有固定的标题 View ，但由于某种原因，这在 JSQMessagesViewController 子类中不起作用。我已经添加了
self.collectionView.collectionViewLayout.sectionHeadersPinToVisibleBounds = true
查看DidLoad()</p>
<p>我尝试的另一个解决方案(来自这篇文章 <a href="https://stackoverflow.com/q/13511733/6394244" rel="noreferrer noopener nofollow">How to make Supplementary View float in UICollectionView as Section Headers do in UITableView plain style</a> )是继承 JSQMessagesCollectionViewFlowLayout，这几乎奏效了。向上滑动时，标题 View 固定在顶部，聊天消息推送到标题 View 下方。但是，当我尝试向下滑动时，当应用崩溃时，我的控制台中会收到以下错误:</p>
<pre class="lang-swift prettyprint-override"><code>*** Assertion failure in -, /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit/UIKit-3512.60.12/UICollectionViewData.m:408
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'layout attributes for supplementary item at index path (<NSIndexPath: 0xc000000000000016> {length = 2, path = 0 - 0}) changed from <JSQMessagesCollectionViewLayoutAttributes: 0x13f65a730> index path: (<NSIndexPath: 0xc000000000000016> {length = 2, path = 0 - 0}); element kind: (UICollectionElementKindSectionHeader); frame = (0 0; 414 100); zIndex = 10;to <JSQMessagesCollectionViewLayoutAttributes: 0x13f679920> index path: (<NSIndexPath: 0xc000000000000016> {length = 2, path = 0 - 0}); element kind: (UICollectionElementKindSectionHeader); frame = (0 10; 414 100); zIndex = 1024;without invalidating the layout'
</code></pre>
<p>有没有人以同样的方式为 JSQMessagesViewController 成功修复了标题 View ？</p>
<p>我改变的方法是
shouldInvalidateLayoutForBoundsChange:
我返回的是，</p>
<p>和 layoutAttributesForElementsInRect: 我改为:</p>
<pre class="lang-swift prettyprint-override"><code>- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
NSMutableArray *attributesInRect = [ mutableCopy];
// if (self.springinessEnabled) {
// NSMutableArray *attributesInRectCopy = ;
// NSArray *dynamicAttributes = ;
//
// //avoid duplicate attributes
// //use dynamic animator attribute item instead of regular item, if it exists
// for (UICollectionViewLayoutAttributes *eachItem in attributesInRect) {
//
// for (UICollectionViewLayoutAttributes *eachDynamicItem in dynamicAttributes) {
// if (
// && eachItem.representedElementCategory == eachDynamicItem.representedElementCategory) {
//
// ;
// ;
// continue;
// }
// }
// }
//
// attributesInRect = attributesInRectCopy;
// }
UICollectionView * const cv = self.collectionView;
CGPoint const contentOffset = cv.contentOffset;
NSMutableIndexSet *missingSections = ;
for (UICollectionViewLayoutAttributes *layoutAttributes in attributesInRect) {
if () {
;
}
}
[attributesInRect enumerateObjectsUsingBlock:^(JSQMessagesCollectionViewLayoutAttributes *attributesItem, NSUInteger idx, BOOL *stop) {
if (attributesItem.representedElementCategory == UICollectionElementCategoryCell) {
;
;
}
else {
attributesItem.zIndex = -1;
}
}];
[missingSections enumerateIndexesUsingBlock:^(NSUInteger idx, BOOL *stop) {
NSIndexPath *indexPath = ;
UICollectionViewLayoutAttributes *layoutAttributes = ;
;
}];
for (UICollectionViewLayoutAttributes *layoutAttributes in attributesInRect){
if () {
NSInteger section = layoutAttributes.indexPath.section;
NSInteger numberOfItemsInSection = ;
NSIndexPath *firstCellIndexPath = ;
NSIndexPath *lastCellIndexPath = ;
NSIndexPath *firstObjectIndexPath = ;
NSIndexPath *lastObjectIndexPath = ;
UICollectionViewLayoutAttributes *firstObjectAttrs;
UICollectionViewLayoutAttributes *lastObjectAttrs;
if (numberOfItemsInSection > 0) {
firstObjectAttrs = ;
lastObjectAttrs = ;
} else {
firstObjectAttrs = ;
lastObjectAttrs = ;
}
CGFloat headerHeight = CGRectGetHeight(layoutAttributes.frame);
CGPoint origin = layoutAttributes.frame.origin;
origin.y = MIN(MAX(contentOffset.y + cv.contentInset.top, (CGRectGetMinY(firstObjectAttrs.frame) - headerHeight)), (CGRectGetMaxY(lastObjectAttrs.frame) - headerHeight));
layoutAttributes.zIndex = 1024;
layoutAttributes.frame = (CGRect) {
.origin = origin, .size = layoutAttributes.frame.size
};
}
}
return attributesInRect;
}
</code></pre></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>我上面提供的代码是可以的。我认为导致崩溃的原因是我在 <code>JSQMessagesViewController</code> 子类中覆盖了 <code>collectionView:collectionViewLayout:referenceSizeForHeaderInSection:</code> 函数。我注释掉了该函数，而是在 <code>JSQMessagesLoadEarlierHeaderView</code> 中的 <code>kJSQMessagesLoadEarlierHeaderViewHeight</code> 常量中设置了高度。是的，我劫持了 LoadEarlierHeaderView 以显示我自己的自定义标题 View 。</p>
<p>现在，标题 View 固定在顶部，显示了我的自定义标题 View ，并且没有任何崩溃。</p></p>
<p style="font-size: 20px;">关于ios - 顶部固定有 SupplementaryView 的 JSQMessagesViewController，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/37499713/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/37499713/
</a>
</p>
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