如何实例化一个collectionview 的cell？

let cell = collectionView.dequeueReusableCellWithReuseIdentifier("BigRoomVideoCell", forIndexPath: indexPath) as VideoViewCell

上面是重用cell的写法， 但是如何每次都实例化一个collectionview的cell？

我尝试过 let cell = VideoViewCell()
直接报
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'the cell returned from -collectionView:cellForItemAtIndexPath: does not have a reuseIdentifier - cells must be retrieved by calling -dequeueReusableCellWithReuseIdentifier:forIndexPath:

google了也没找到合适的答案

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也试过 let cell = collectionView.cellForItemAtIndexPath(indexPath) as VideoViewCell 办法，直接报 fatal error: unexpectedly found nil while unwrapping an Optional value

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是否没有注册

    [_collectionView registerClass:[BigRoomVideoCell class]
    forCellWithReuseIdentifier:CELL_IDENTIFIER];