swift - UICollectionView dequeue 在快速单元测试中引发异常

Question

我正在尝试使用 swift 测试我的 UICollectionViewDataSource，但它在尝试使单元格出队时引发异常。异常似乎没有为重用标识符注册类。在我的 Storyboard 中，我注册了一个类和标识符，所以当我运行该应用程序时工作正常，但我正在尝试单独测试

//  CollectionViewDataSource.swift
import UIKit

class CollectionViewDataSource : NSObject, UICollectionViewDataSource {

  private var items = [MediaItem]()

    init(items: [MediaItem]) {
      self.items = items
    }

  func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return self.items.count
  }

  func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
    return 1
  }

  func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {

    let cell = collectionView.dequeueReusableCellWithReuseIdentifier("Cell", forIndexPath: indexPath) as MediaItemCell

      // .. cell property setting

      return cell
  }

}

测试文件

//  CollectionViewDataSourceTests.swift
import UIKit
import XCTest

class CollectionViewDataSourceTests: XCTestCase {

  var dataSource: CollectionViewDataSource!
    var collectionView: UICollectionView?

    override func setUp() {
      super.setUp()

        let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
        let size = CGRect(x: 0, y: 0, width: 100, height: 100)
        collectionView = UICollectionView(frame: size, collectionViewLayout: layout)

        let movieA = Movie(title: "Title", year: 1980, slug: "", banner: "")
        let movieB = Movie(title: "", year: 1980, slug: "", banner: "")
        let items = [movieA, movieB]
        dataSource = CollectionViewDataSource(items: items)

    }

  // This crashes when attempting to dequeue a cell. It's as if the collection
  // view never registers the class properly
  func testDataSourceReturnsACell() {
    let indexPath = NSIndexPath(forItem: 0, inSection: 0)

      // Register the cell
      collectionView!.registerClass(MediaItemCell.self, forCellWithReuseIdentifier: "Cell")
      let cell = dataSource.collectionView(collectionView!, cellForItemAtIndexPath: indexPath) as MediaItemCell
      XCTAssert(cell.textLabel.text == "The Shawshank Redemption", "Data source should set cell text")

  }

}

Answer 1

有趣的是，这个测试引发异常的原因是因为我从未将 collectionView 和 dataSource 链接在一起。我认为这意味着 UICollectionView 不允许您在没有数据源的情况下注册单元格。固定代码如下:

func testDataSourceReturnsACell() {
    let indexPath = NSIndexPath(forItem: 0, inSection: 0)
    collectionView!.dataSource = dataSource // d'oh
    collectionView!.registerClass(MediaItemCell.self, forCellWithReuseIdentifier: "Cell")
    let cell = dataSource.collectionView(collectionView!, cellForItemAtIndexPath: indexPath) as MediaItemCell
    XCTAssert(cell.textLabel.text == "The Shawshank Redemption", "Data source should set cell text")
}