Question

昨天我在github上发现了一个pod：3lvis/DATASource。自定义类DATASource具有：

初始化

private init(cellIdentifier: String, fetchRequest: NSFetchRequest, mainContext: NSManagedObjectContext, sectionName: String? = nil, tableConfiguration: ((cell: UITableViewCell, item: NSManagedObject, indexPath: NSIndexPath) -> ())?, collectionConfiguration: ((cell: UICollectionViewCell, item: NSManagedObject, indexPath: NSIndexPath) -> ())?) {
    self.cellIdentifier = cellIdentifier
    self.fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: mainContext, sectionNameKeyPath: sectionName, cacheName: nil)
    self.tableConfigurationBlock = tableConfiguration
    self.collectionConfigurationBlock = collectionConfiguration

    super.init()

    self.fetchedResultsController.delegate = self
    self.fetch()
}

关闭为私有var：

private var tableConfigurationBlock: ((cell: UITableViewCell, item:     NSManagedObject, indexPath: NSIndexPath) -> ())?

内部功能：

internal func configureCell(cell: UIView, indexPath: NSIndexPath) {
    var item: NSManagedObject?

    let rowIsInsideBounds = indexPath.row <  self.fetchedResultsController.fetchedObjects?.count
    if rowIsInsideBounds {
        item = self.fetchedResultsController.objectAtIndexPath(indexPath) as? NSManagedObject
    }

    if let item = item {
        if let _ = self.tableView, configuration = self.tableConfigurationBlock {
            configuration(cell: cell as! UITableViewCell, item: item, indexPath: indexPath)
        } else if let _ = self.collectionView, configuration = self.collectionConfigurationBlock {
            configuration(cell: cell as! UICollectionViewCell, item: item, indexPath: indexPath)
        }
    }
}

来自UITableViewDatasource的公共函数：

public func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCellWithIdentifier(self.cellIdentifier, forIndexPath: indexPath)

    self.configureCell(cell, indexPath: indexPath)

    return cell
}

然后我们创建Viewcontroller并将DATASource初始化为一个惰性变量：

lazy var dataSource: DATASource = {
    let request: NSFetchRequest = NSFetchRequest(entityName: "User")
    request.sortDescriptors = [
        NSSortDescriptor(key: "name", ascending: true),
        NSSortDescriptor(key: "firstLetterOfName", ascending: true)
    ]

    let dataSource = DATASource(tableView: self.tableView, cellIdentifier: CustomCell.Identifier, fetchRequest: request, mainContext: self.dataStack!.mainContext, sectionName: "firstLetterOfName", configuration: { cell, item, indexPath in
        if let cell = cell as? CustomCell {
            cell.label.text = item.valueForKey("name") as? String
        }
    })
    return dataSource

}()

对我来说非常有意思的是那个带有配置块的lazy var的一部分，它没有被第一次调用，只有当tableView在indexPath上询问他的委托单元格中的行时才被调用：

configuration: { cell, item, indexPath in
        if let cell = cell as? CustomCell {
            cell.label.text = item.valueForKey("name") as? String
        }
    })

我搜索了几个小时，但没有找到任何解释。所以我写了一些代码并测试了它。它确实有效！

public class Closuretest {
  private var ConfigurationBlock: ((name: String, type: String) -> ())?


  init(configuration: (name: String, type: String) -> ()) {
    self.ConfigurationBlock = configuration
  }

  //Internal func that will be called by func print
  internal func configureBlock(name: String, type: String) {
    if let conf = self.ConfigurationBlock {
      conf(name: name, type: type)
    }
  }

  public func setLabel(name: String, type: String) {
    self.configureBlock(name, type: type)
  }
}
//New class that will initialize new var with Closuretest var
class NewClass {
  lazy var closure: Closuretest = {
    let test = Closuretest(configuration: { (name, type) in
      print(name)
      print(type)
  })
  return test
  }()

  func giveMeString(name: String, type: String) {
    closure.setLabel(name, type: type)
  }
}

var testVar = NewClass()
testVar.giveMeString("Just a String", type: "True")

所以问题，为什么它有效，为什么这个配置块（闭包变量）仅在类的内部函数调用它时调用？如何调用那种类型的代码，init或者有人可以告诉你发生了什么？

Swift Closure作为在由函数

0 个答案: