Question

我正在研究一个聊天应用程序示例。

我想在加载所有数据后向下滚动，但是我的代码不起作用。它会加载所有数据，对它们进行排序并显示，但不会向下滚动到最后一条消息。

这是我的代码，我在其中加载所有数据并想向下滚动：

 //Downloads messages
func fetchData() {
    Message.downloadAllMessages(forUserID: (currentUser?.uid)!, completion: {[weak weakSelf = self] (message) in
        weakSelf?.items.append(message)
        weakSelf?.items.sort{ $0.timestamp < $1.timestamp }
        DispatchQueue.main.async {
            if let state = weakSelf?.items.isEmpty, state == false {
                weakSelf?.tableView.reloadData()
                weakSelf?.tableView.scrollToRow(at: IndexPath.init(row: self.items.count - 1, section: 0), at: .bottom, animated: false)
            }
        }
    })
    Message.markMessagesRead(forUserID: (currentUser?.uid)!)
}

这是我的自定义：

 func customization() {
    self.imagePicker.delegate = self
    self.tableView.estimatedRowHeight = self.barHeight
    self.tableView.rowHeight = UITableView.automaticDimension
    self.tableView.contentInset.bottom = self.barHeight
    self.tableView.scrollIndicatorInsets.bottom = self.barHeight
    self.navigationItem.title = self.currentUser?.username
    self.locationManager.delegate = self

    //ContainerView customization
    let extraViewsContainer = UIView.init()
    extraViewsContainer.translatesAutoresizingMaskIntoConstraints = false
    self.view.addSubview(extraViewsContainer)
    self.topAnchorContraint = NSLayoutConstraint.init(item: extraViewsContainer, attribute: .top, relatedBy: .equal, toItem: self.view, attribute: .top, multiplier: 1, constant: 1000)
    self.topAnchorContraint.isActive = true
    extraViewsContainer.leadingAnchor.constraint(equalTo: self.view.leadingAnchor).isActive = true
    extraViewsContainer.trailingAnchor.constraint(equalTo: self.view.trailingAnchor).isActive = true
    extraViewsContainer.heightAnchor.constraint(equalTo: self.view.heightAnchor, multiplier: 1).isActive = true
    extraViewsContainer.backgroundColor = UIColor.clear

    //PreviewView Customization
    extraViewsContainer.addSubview(self.previewView)
    self.previewView.isHidden = true
    self.previewView.translatesAutoresizingMaskIntoConstraints = false
    self.previewView.leadingAnchor.constraint(equalTo: extraViewsContainer.leadingAnchor).isActive = true
    self.previewView.topAnchor.constraint(equalTo: extraViewsContainer.topAnchor).isActive = true
    self.previewView.trailingAnchor.constraint(equalTo: extraViewsContainer.trailingAnchor).isActive = true
    self.previewView.bottomAnchor.constraint(equalTo: extraViewsContainer.bottomAnchor).isActive = true
    self.scrollView.minimumZoomScale = 1.0
    self.scrollView.maximumZoomScale = 3.0
    //MapPreView Customization
    extraViewsContainer.addSubview(self.mapPreviewView)
    self.mapPreviewView.isHidden = true
    self.mapPreviewView.translatesAutoresizingMaskIntoConstraints = false
    self.mapPreviewView.leadingAnchor.constraint(equalTo: extraViewsContainer.leadingAnchor).isActive = true
    self.mapPreviewView.topAnchor.constraint(equalTo: extraViewsContainer.topAnchor).isActive = true
    self.mapPreviewView.trailingAnchor.constraint(equalTo: extraViewsContainer.trailingAnchor).isActive = true
    self.mapPreviewView.bottomAnchor.constraint(equalTo: extraViewsContainer.bottomAnchor).isActive = true
    //NotificationCenter for showing extra views
    NotificationCenter.default.addObserver(self, selector: #selector(self.showExtraViews(notification:)), name: NSNotification.Name(rawValue: "showExtraView"), object: nil)

}

我在viewDidLoad中同时调用fetchData和customization，也许customization中有一些问题

在此先感谢您的帮助！

Answer 1

您可以尝试在selectRow之前使用didSelectRowAt和scrollToRow，

DispatchQueue.main.async {
        if let state = weakSelf?.items.isEmpty, state == false {
            weakSelf?.tableView.reloadData()
            let indexPath = IndexPath.init(row: self.items.count - 1, section: 0)
            weakSelf?.tableView.selectRow(at: indexPath, animated: true, scrollPosition: .none)
            weakSelf?.tableView.delegate?.tableView?(weakSelf?.tableView, didSelectRowAt: indexPath)
            weakSelf?.tableView.scrollToRow(at: indexPath, at: .bottom, animated: true)
        }
    }

加载数据后如何滚动到行？

1 个答案: