ios - 当用户滚动到最后一个 tableViewCell 时执行操作

Question

上下文

• 构建一种新闻源

问题

• 我需要在用户滚动到最后一个表格 View 单元格时加载更多帖子
• 我不知道从哪里开始，如何实现，在代码中的什么位置
• 所以基本上我需要在用户滚动到最后一个表格 View 时调用服务器下载帖子，将这些帖子附加到当前表格 View 的底部

这是相关的代码片段(我认为!)

class GeneralPostAreaController: UIViewController {
        ...
        extension GeneralPostAreaController: UITableViewDataSource {

    func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

        return PostsCollection.postsFromParse.posts.count

    }

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCellWithIdentifier("PostCell") as! PostTableViewCell
        cell.postImage.image = PostsCollection.postsFromParse.posts[indexPath.row].image
        cell.postName.text = PostsCollection.postsFromParse.posts[indexPath.row].name
        cell.postText.text = PostsCollection.postsFromParse.posts[indexPath.row].text

        cell.loadAudio = PostsCollection.postsFromParse.posts[indexPath.row].audioObject.parseAudioData
        return cell
    }

}

这是我用来从服务器获取数据的代码 (Parse)。请原谅可怕的数据结构，这是我的第一个应用程序!

    class ParseQueryer: NSObject{

//HAVE TO RESTRUCTURE

var posts: [Post] = []

//this is not a very elegant way to reload table Data
func getPosts(selectedTableView: UITableView){

var query = PFQuery(className: "Post")
query.addDescendingOrder("createdAt")
query.limit = 10
query.findObjectsInBackgroundWithBlock {(result: [AnyObject]?, error: NSError?) -> Void in
    self.posts = result as? [Post] ?? []

    selectedTableView.reloadData()

    for post in self.posts{
        post.name = post["Name"] as? String
        post.text = post["Text"] as? String
        //println(post.text)
        if let audioData = post["Audio"] as? PFFile {
            audioData.getDataInBackgroundWithBlock({
                (audioData: NSData?, error: NSError?) -> Void in
                if (error == nil){
                    post.audioObject.parseAudioData = audioData
                }
            })
        }
        if let imgData = post["Photo"] as? PFFile {
            imgData.getDataInBackgroundWithBlock({
                (imageData: NSData?, error: NSError?) -> Void in
                if (error == nil){
                    let image = UIImage(data: imageData!)
                    post.image = image
                }
            })
        }

    }
}
    selectedTableView.reloadData()

我看了答案here但这对我来说没有意义。

Answer 1

所以 UITableView 继承自 UIScrollView 所以你可以使用 scrollview 委托(delegate)方法来知道你何时滚动到底部。

    override func scrollViewDidScroll(scrollView: UIScrollView) {

       //1. decide on the distance from the bottom that if the user scrolls to that point you will load more results
        let minimumTrigger = scrollView.bounds.size.height + self.triggerDistanceFromBottom

        // 2. Now you are checking to see that the height of all the content in the scrollview/tableView.( i.e. all the cells hights stacked ontop of eachother) is greater than the minimum height for triggering a load
       // This step is so that if you have only a few results, the loadMoreResults method won't constantly be called. 
        if scrollView.contentSize.height > minimumTrigger {

           //3. This calculated the distance from the bottom of the scrollview. 
            let distanceFromBottom = scrollView.contentSize.height - (scrollView.bounds.size.height - scrollView.contentInset.bottom) - scrollView.contentOffset.y

            //4. then this is the crucial check.
            if distanceFromBottom < self.scrollTriggerDistanceFromBottom {
                // Do your stuff
            }
        }

    }