Swift实现UITableView分页滚动：每页5条，滚动切换页码

Hey there! Let's fix your code to meet that page-switching scrolling requirement. I'll break down what's missing and how to adjust it step by step.

First, let's go over the gaps in your current code:

• When you scroll to the bottom, you increment currentPage but don't actually fetch the new page's data (you just reload the table with existing items).
• There's no logic to detect scrolling to the top to switch to the previous page.
• You're appending new items to the array every time, which would accumulate all pages instead of showing only the current page's 5 items.
• No loading state to prevent duplicate requests if the user scrolls repeatedly before the data loads.

Here's the modified code with all the fixes:

First, add a loading flag to avoid concurrent requests:

var currentPage: Int = 1
var listLimit: Int = 5
var isLoading = false // Add this to prevent duplicate API calls

Then update your updatePropertyListWithDistrict function to handle loading state, clear the array for page switching, and safely handle the response:

func updatePropertyListWithDistrict(district: String) {
    guard !isLoading else { return } // Don't proceed if already loading data
    isLoading = true
    MBProgressHUD.showAdded(to: self.view, animated: true) // Show loading indicator while fetching
    
    PSPWCFService.sharedClient.PropertyList(district: district, PageNumber: currentPage, PageSize: listLimit) { (json, error) in
        // Ensure we always hide the HUD and reset loading state, even if there's an error
        defer {
            MBProgressHUD.hide(for: self.view, animated: true)
            self.isLoading = false
        }
        
        if let error = error {
            print(error.localizedDescription)
            // Optional: Show an error alert to the user here for better UX
            return
        }
        
        let jsonArray = json?.array ?? [] // Safely unwrap to avoid crashes if JSON is invalid
        self.properties.removeAll() // Clear existing items to show only current page's 5 items
        for object in jsonArray {
            let newProperty = Property(json: object)
            self.properties.append(newProperty)
        }
        
        self.tableView.reloadData()
        
        if self.properties.isEmpty {
            let alertController = UIAlertController(title: "Alert", message: "No listings available in the area.", preferredStyle: .alert)
            alertController.addAction(UIAlertAction(title: "Dismiss", style: .default))
            self.present(alertController, animated: true)
        }
    }
}

Next, update the scrollViewDidEndDragging method to detect both bottom (next page) and top (previous page) scrolls:

func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
    guard scrollView == tableView, !isLoading else { return } // Only act on the table view and if not loading
    
    // Check if scrolled to the bottom to load next page
    let isAtBottom = (scrollView.contentOffset.y + scrollView.frame.size.height) >= scrollView.contentSize.height
    if isAtBottom {
        currentPage += 1
        updatePropertyListWithDistrict(district: "ABC")
        // Optional: Scroll to the top of the new page after loading for smoother transition
        // tableView.scrollToRow(at: IndexPath(row: 0, section: 0), at: .top, animated: true)
        return
    }
    
    // Check if scrolled to the top to load previous page (only if not on the first page)
    let isAtTop = scrollView.contentOffset.y <= 0
    if isAtTop && currentPage > 1 {
        currentPage -= 1
        updatePropertyListWithDistrict(district: "ABC")
        // Optional: Scroll to the bottom of the previous page after loading
        // tableView.scrollToRow(at: IndexPath(row: properties.count - 1, section: 0), at: .bottom, animated: true)
    }
}

Key changes explained:

1. Loading State: The isLoading flag prevents overlapping API calls if the user scrolls quickly before the previous request finishes.
2. Page Switching: We clear the properties array before adding new items so each page only shows 5 items (matches your "switch to next/previous page" requirement). If you want infinite scroll (accumulate all loaded items instead of switching), just remove the self.properties.removeAll() line.
3. Top Scroll Detection: Added logic to trigger the previous page when the user scrolls to the top (as long as we're not on page 1).
4. Safe Handling: Replaced force unwrapping of jsonArray with a safe default to avoid crashes, and used defer to ensure loading state and HUD are always reset.
5. Loading Indicator: Added showing the HUD when the request starts (your original code only hid it).

内容的提问来源于stack exchange，提问作者William Loke