swift - 过滤 Realm 时显示 NSProgressIndicator

Question

设置:

一个 Swift 3 应用程序，RealmSwift 2.10.1，带有一个按钮、tableview 和一个不确定的旋转进度指示器(旋转的圆圈)

目标:

当用户点击按钮时，查询大型 Realm 数据库(百万条记录)并在等待结果期间显示进度指示器。

问题:

进度指示器在过滤器完成后才会显示。

代码:

//called from button click
func performFilterAction() {  
     self.filterProgressIndicator.isHidden = false
     self.filterProgressIndicator.startAnimation(nil)
     let predicate = NSPredicate(format: "location = %@", "US")
     let realm = try! Realm()
     self.results = realm.objects(MyClass.self).filter(predicate)
     self.tableView.reloadData()
     self.filterProgressIndicator.isHidden = true
}

上面的代码为美国的所有位置过滤了 Realm，并填充了一个数组，该数组用作 tableView 的数据源。

其他:

另一个问题是，即使进度指示器隐藏在代码末尾，它也不会隐藏在 UI 中。

我试过在后台线程上实现过滤代码:

func performFilterAction() {
     self.filterProgressIndicator.isHidden = false
     self.filterProgressIndicator.startAnimation(nil)

     DispatchQueue.global(qos: .background).async {  
          let predicate = NSPredicate(format: "location = %@", "US")
          let realm = try! Realm()
          self.results = realm.objects(MyClass.self).filter(predicate)
          DispatchQueue.main.async {
              self.tableView.reloadData()
              self.filterProgressIndicator.isHidden = true
          }
     }
}

它在过滤之前确实显示了 progressIndicator，但在 tableView 重新加载时崩溃并出现以下错误

This application is modifying the autolayout engine from a background thread after the engine was accessed from the main thread. This can lead to engine corruption and weird crashes.

另一个尝试:

根据提供的答案，我实现了这样的收集通知

func performFilterAction1() {
    self.filterProgressIndicator.isHidden = false
    self.filterProgressIndicator.startAnimation(nil)
    let predicate = NSPredicate(format: "location = %@", "US")
    let realm = try! Realm()
    self.results = realm.objects(MyClass.self).filter(predicate)

    self.notificationToken = self.results.addNotificationBlock { [weak self] (changes: RealmCollectionChange) in
        guard let tableView = self?.filterTableView else { return }
        switch changes {
        case .initial:
            // Results are now populated and can be accessed without blocking the UI
            tableView.reloadData()
            self?.filterProgressIndicator.isHidden = true
            break
        case .update(_, let deletions, let insertions, let modifications):
            break
        case .error(let error):
            // An error occurred while opening the Realm file on the background worker thread
            fatalError("\(error)")
            break
        }
    }
}

这样做的结果:进度指示器在过滤器完成之前不会显示，它只是暂时“闪烁”。

每个请求:回溯

772.00 ms   58.7%   0 s      Main Thread  0x72995
742.00 ms   56.5%   0 s       start
742.00 ms   56.5%   0 s        main
742.00 ms   56.5%   0 s         NSApplicationMain
625.00 ms   47.6%   1.00 ms          -[NSApplication run]
377.00 ms   28.7%   0 s           -[NSApplication(NSEvent) sendEvent:]
342.00 ms   26.0%   0 s            -[NSWindow(NSEventRouting) sendEvent:]
342.00 ms   26.0%   0 s             -[NSWindow(NSEventRouting) _reallySendEvent:isDelayedEvent:]
342.00 ms   26.0%   0 s              -[NSWindow(NSEventRouting) _handleMouseDownEvent:isDelayedEvent:]
331.00 ms   25.2%   0 s               -[NSControl mouseDown:]
330.00 ms   25.1%   0 s                -[NSButtonCell trackMouse:inRect:ofView:untilMouseUp:]
330.00 ms   25.1%   0 s                 -[NSCell trackMouse:inRect:ofView:untilMouseUp:]
319.00 ms   24.2%   0 s                  _os_activity_initiate_impl
319.00 ms   24.2%   0 s                   -[NSButtonCell _sendActionFrom:]
319.00 ms   24.2%   0 s                    -[NSCell _sendActionFrom:]
319.00 ms   24.2%   0 s                     _os_activity_initiate_impl
319.00 ms   24.2%   0 s                      __26-[NSCell _sendActionFrom:]_block_invoke
319.00 ms   24.2%   0 s                       -[NSControl sendAction:to:]
319.00 ms   24.2%   0 s                        -[NSApplication(NSResponder) sendAction:to:from:]
318.00 ms   24.2%   0 s                         _os_activity_initiate_impl
259.00 ms   19.7%   0 s                          @objc FilterVC.filterAction(Any) -> ()
259.00 ms   19.7%   0 s                           FilterVC.filterAction(Any) -> ()
257.00 ms   19.5%   0 s                            FilterVC.test() -> ()
238.00 ms   18.1%   0 s                             Results.count.getter
238.00 ms   18.1%   0 s                              -[RLMResults count]
238.00 ms   18.1%   0 s                               -[RLMResults count]::$_1::operator()() const
238.00 ms   18.1%   0 s                                realm::Results::size()
238.00 ms   18.1%   0 s                                 realm::Query::count(unsigned long, unsigned long, unsigned long) const
238.00 ms   18.1%   0 s                                  realm::Query::aggregate_internal(realm::Action, realm::DataType, bool, realm::ParentNode*, realm::QueryStateBase*, unsigned long, unsigned long, realm::SequentialGetterBase*) const

Answer 1

这是 Realm's collection notifications 的完美用例.这看起来像:

var notificationToken: NotificationToken? = nil
var results: Results<MyClass>? = nil

func performFilterAction() {
  filterProgressIndicator.isHidden = false
  filterProgressIndicator.startAnimation(nil)

  let realm = try! Realm()
  results = realm.objects(MyClass.self).filter("location = %@", "US")
  notificationToken = results.addNotificationBlock { [weak self] (changes: RealmCollectionChange) in
    guard let tableView = self?.tableView else { return }
    switch changes {
    case .initial:
      // Results are now populated and can be accessed without blocking the UI
      tableView.reloadData()
      self.filterProgressIndicator.isHidden = true
      break
    case .update(_, let deletions, let insertions, let modifications):
      // Query results have changed, so apply them to the UITableView
      tableView.beginUpdates()
      tableView.insertRows(at: insertions.map({ IndexPath(row: $0, section: 0) }),
                         with: .automatic)
      tableView.deleteRows(at: deletions.map({ IndexPath(row: $0, section: 0)}),
                         with: .automatic)
      tableView.reloadRows(at: modifications.map({ IndexPath(row: $0, section: 0) }),
                         with: .automatic)
      tableView.endUpdates()
      break
    case .error(let error):
      // An error occurred while opening the Realm file on the background worker thread
      fatalError("\(error)")
      break
    }
  }
}

deinit {
  notificationToken?.stop()
}

这使您可以在执行初始过滤时显示进度指示器，还可以在对集合中的数据进行更改时提供动画更新。如果您不关心后者，您也可以在 .update 情况下调用 reloadData()。