列表的一半将在开始时加载，当到达列表的末尾时，另一半将添加到表视图内的下方

Question

我有一个 tableView 和 json 数据。我希望 tableview 加载一半的 json 数据。当表视图滚动到前半部分结束时，另一半将被加载。有人知道我该怎么做吗？

Answer 1

我相信您必须在 scrollViewDidScroll 的帮助下进行一些 pagination 类型的处理，以观察何时到达 tableview 的末尾以加载下一批

首先设置一些初始变量来帮助您跟踪分页过程。

var pageStart = 0
var pageSize = 15

// scrollViewDidScroll will be called several times
// so we need to be able to block the loading process
var isLoadingItems = false

// Array of 50 values which you get from the API
// For example your JSON data
var totalNumberOfItems = (0...49).reduce([Int]())
{ (result, number) in
    
    var array = result
    array.append(number)
    return array
}

// This will periodically be filled with items from totalNumberOfItems
var itemsToLoad: [Int] = []

我创建了这个加载函数，它有助于批量添加项目并适当地重新加载表格视图

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(true)
    loadItems()
}

private func loadItems(withDelay delay: Double = 0) {
    
    // Check that there are items to load
    if pageStart < totalNumberOfItems.count, !isLoadingItems {
        
        isLoadingItems = true
        
        // The delay and dispatch queue is just to show you the
        // loading of data in batches, it is not needed for the
        // solution
        if delay > 0 {
            presentLoader()
        }
        
        DispatchQueue.main.asyncAfter(deadline: .now() + delay) {
            
            if delay > 0 {
                
                // dismiss the loader
                self.dismiss(animated: true, completion: nil)
            }
            
            // Calculate the page end based on the page size or on
            // the number of items remaining to load if the page size
            // is greater than the number of items remaining
            var pageEnd = self.pageStart + self.pageSize - 1
            
            if pageEnd > self.totalNumberOfItems.count {
                let remainingItems = self.totalNumberOfItems.count - self.pageStart - 1
                pageEnd = self.pageStart + remainingItems
            }
            
            let newItems = Array(self.totalNumberOfItems[self.pageStart ... pageEnd])
            self.itemsToLoad.append(contentsOf: newItems)
            self.pageStart = pageEnd + 1
            
            let indexPaths = newItems.map { IndexPath(row: $0,
                                                      section: 0) }
            
            // Update the table view
            self.tableView.beginUpdates()
            self.tableView.insertRows(at: indexPaths, with: .fade)
            self.tableView.endUpdates()
            
            // scroll to first newly inserted row
            if let firstNewRow = indexPaths.first {
                self.tableView.scrollToRow(at: firstNewRow,
                                           at: .top,
                                           animated: true)
            }
            
            
            // Unlock the loading process
            self.isLoadingItems = false
        }
    }
}

然后观察是否使用 scrollViewDidScroll 到达末尾并重新加载表格视图以显示插入的行

override func scrollViewDidScroll(_ scrollView: UIScrollView) {
    
    // Check that the current scroll offset is > 0 so you don't get
    // any false positives when the table view is set up
    // and check if the current offset has reached the end
    if scrollView.contentOffset.y >= 0 &&
        scrollView.contentOffset.y >= (scrollView.contentSize.height - scrollView.frame.size.height) {
        
        print("reached end, load more")
        
        // Load more data
        loadItems(withDelay: 1)
    }
}

如下所示：

如果您发现某些部分难以理解或添加到您自己的代码中，可以找到可以按原样运行的完整代码 此处：