ios - 在不重新加载所有数据的情况下更新 UIImageView

Question

这几天一直被这个问题困扰。在触发长按手势之前，我将 ImageView 设置为不可见。但是，我无法全神贯注于如何使 UIImageView 在此之后变得可见。这是在 tableView 的一个 Cell 中。我使用了 reloadData()，但问题是表格丢失了它的位置。当您松开手指时，它会向上滚动。长手势触发数据库端的 bool 值，用于切换 saveShow。加载数据时，查询会检查并显示 UIImageView(如果为真)。所以我相信我必须重新加载数据，因为它是基于查询的..？任何帮助将不胜感激!

class SecondViewController: UIViewController, UITableViewDelegate, UITableViewDataSource, UIPickerViewDelegate, UIPickerViewDataSource {

    let db = DatabaseController()

    @IBOutlet weak var tableView: UITableView!
    @IBOutlet weak var cityPicker: UIPickerView!

    override func viewDidLoad() {
        super.viewDidLoad()
        tableView.delegate = self
        tableView.dataSource = self
        cityPicker.delegate = self
        cityPicker.dataSource = self

        self.tableView.autoresizingMask = UIView.AutoresizingMask.flexibleHeight;
        self.db.createTable()

        //////////////////////////////////////////////////////////////////
        let longPressGesture:UILongPressGestureRecognizer = UILongPressGestureRecognizer(target: self, action: #selector(longPress))
        longPressGesture.minimumPressDuration = 1.0 // 1 second press
        longPressGesture.delegate = self as? UIGestureRecognizerDelegate
        self.tableView.addGestureRecognizer(longPressGesture)
        ////////////////////////////////////////////////////////////////


        ////////////////////////////////////////////////////
        Alamofire.request("http://url.com/jsonfile").responseJSON { response in
            if (response.result.value != nil) {
                let strOutput = JSON(response.result.value ?? "nil")

                if let resObj = strOutput.arrayObject {
                    arrRes2 = resObj as! [[String:AnyObject]]
                    self.db.addShowsToDatabase(arrRes: arrRes2)
                }
            }

            self.db.deleteOldShows()
            self.grabData(id: 1)
            self.tableView.reloadData()
        }
        ////////////////////////////////////////////////////////////////////
    }

    func grabData(id: Int) -> Void {
        regionResults = self.db.listAllShows(id: id)
        self.tableView.reloadData()
    }

    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }

    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return cities.count
    }

    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return cities[row]
    }

    func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        cheapFix = row + 1
        grabData(id: row + 1)
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        if regionResults.isEmpty {
            return 1
        } else {
            return regionResults.count
        }
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "bandCustomCell") as! BandTableViewCell
        if regionResults.isEmpty {
            cell.bandPic.image = UIImage(named: "flyer.jpg")
            cell.bandSummary?.text = "No Shows Announced!"
            cell.bandVenue?.text = "None"
            cell.bandDate?.text = "None"
        } else {
            let show = regionResults[indexPath.row]
            //print(try! show.get(Expression<String>("show_summary")))

            let strDateFull = try! show.get(Expression<String>("show_date"))
            var strDate: Array = ((strDateFull as AnyObject).components(separatedBy: "T"))

            // Setting up the date
            var dateArr: Array = strDate[0].components(separatedBy: "-")
            let dateStr: String = "\(dateArr[1])-\(dateArr[2])-\(dateArr[0])"

            // Setting up the time
            var timeArr: Array = strDate[1].components(separatedBy: ":")
            var timeStr: Int? = Int(timeArr[0])

            // Changing military time to standard
            if timeStr! > 12 {
                timeStr = timeStr! - 12
            }
            let saved = try! show.get(Expression<Bool>("save_show"))

            if (saved == true) {
                cell.bandSavedShow.isHidden = false
            } else if (saved == false) {
                cell.bandSavedShow.isHidden = true
            }

            cell.bandSummary?.text = "\(try! show.get(Expression<String>("show_summary"))), \(timeStr!):\(timeArr[1])PM"
            cell.bandVenue?.text = try! show.get(Expression<String>("venue_name"))
            /*if (show["shows_img"] as? String != "null") {
                let url = URL(string: show["shows_img"] as! String)
                cell.bandPic.kf.setImage(with: url)
            } else {*/
            cell.bandPic.image = UIImage(named: "flyer.jpg")
            //}
            cell.bandDate?.text = dateStr

            tableView.isScrollEnabled = true

        }
        return cell
    }

    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {

        myIndex2 = indexPath.row
        //performSegue(withIdentifier: "segue2", sender: self)
    }

    @objc func longPress(_ longPressGestureRecognizer: UILongPressGestureRecognizer) {
        if longPressGestureRecognizer.state == UIGestureRecognizer.State.began {
            let touchPoint = longPressGestureRecognizer.location(in: self.tableView)
            if let indexPath = self.tableView.indexPathForRow(at: touchPoint) {

                let show = regionResults[indexPath.row]
                let summary = try! show.get(Expression<String>("show_summary"))
                let date = try! show.get(Expression<String>("show_date"))
                let saved = try! show.get(Expression<Bool>("save_show"))

                self.db.toogleSaveShows(summary: summary, date: date, saved: saved)
                reload(tableView: self.tableView, indexPath: indexPath)
            }
            //grabData(id: cheapFix)

        }
    }

    func reload(tableView: UITableView, indexPath: IndexPath) {
        //found on stackoverflow
        let contentOffset = tableView.contentOffset
        tableView.beginUpdates()
        tableView.reloadRows(at: [indexPath], with: UITableView.RowAnimation.none)
        tableView.setContentOffset(contentOffset, animated: false)
        tableView.endUpdates()
    }
}

Answer 1

如下更新 longPressGesture 方法:

let touchPoint = longPressGestureRecognizer.location(in: self.tableView)
        if let indexPath = self.tableView.indexPathForRow(at: touchPoint) {
              let cell = tableView.cellForRow(at: indexPath) as? BandTableViewCell;
              cell.bandPic.image = ....//provide image here.
        }

在这里，不需要重新加载整个表格，而只是访问单元格并在那里设置 ImageView 。