From b23d6f901d722b07f3099b74789f588a0a01d907 Mon Sep 17 00:00:00 2001
From: llwijvbw123 <llwijvbw123@gmail.com>
Date: Thu, 27 May 2021 09:47:34 +0800
Subject: [PATCH] =?UTF-8?q?=E8=A7=A3=E5=86=B3header=20=E5=9B=A0=E9=87=8D?=
 =?UTF-8?q?=E7=94=A8=E6=8F=90=E5=89=8D=E9=9A=90=E8=97=8F?=
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借鉴代码:https://github.com/HebeTienCoder/XLPlainFlowLayout/blob/master/XLPlainFlowLayout/XLPlainFlowLayout.m
---
 .../XPCollectionViewWaterfallFlowLayout.m     | 35 +++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/Example/WaterfallLayout/XPCollectionViewWaterfallFlowLayout.m b/Example/WaterfallLayout/XPCollectionViewWaterfallFlowLayout.m
index 2494f68..49c4ae0 100644
--- a/Example/WaterfallLayout/XPCollectionViewWaterfallFlowLayout.m
+++ b/Example/WaterfallLayout/XPCollectionViewWaterfallFlowLayout.m
@@ -146,6 +146,41 @@ - (CGSize)collectionViewContentSize {
             [result addObject:attribute];
         }
     }];
+    //创建存索引的数组，无符号（正整数），无序（不能通过下标取值），不可重复（重复的话会自动过滤）
+    NSMutableIndexSet *noneHeaderSections = [NSMutableIndexSet indexSet];
+    //遍历superArray，得到一个当前屏幕中所有的section数组
+    for (UICollectionViewLayoutAttributes *attributes in result)
+    {
+        //如果当前的元素分类是一个cell，将cell所在的分区section加入数组，重复的话会自动过滤
+        if (attributes.representedElementCategory == UICollectionElementCategoryCell)
+        {
+            [noneHeaderSections addIndex:attributes.indexPath.section];
+        }
+    }
+
+    //遍历superArray，将当前屏幕中拥有的header的section从数组中移除，得到一个当前屏幕中没有header的section数组
+    //正常情况下，随着手指往上移，header脱离屏幕会被系统回收而cell尚在，也会触发该方法
+    for (UICollectionViewLayoutAttributes *attributes in result) {
+        //如果当前的元素是一个header，将header所在的section从数组中移除
+        if ([attributes.representedElementKind isEqualToString:UICollectionElementKindSectionHeader]) {
+            [noneHeaderSections removeIndex:attributes.indexPath.section];
+        }
+    }
+
+    //遍历当前屏幕中没有header的section数组
+    [noneHeaderSections enumerateIndexesUsingBlock:^(NSUInteger idx, BOOL *stop) {
+
+        //取到当前section中第一个item的indexPath
+        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:idx];
+        //获取当前section在正常情况下已经离开屏幕的header结构信息
+        UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader atIndexPath:indexPath];
+
+        //如果当前分区确实有因为离开屏幕而被系统回收的header
+        if (attributes) {
+            //将该header结构信息重新加入到superArray中去
+            [result addObject:attributes];
+        }
+    }];
     
     // Header view hover.
     if (_sectionHeadersPinToVisibleBounds) {