Question

我想在UICollectionViewCells显示后显示3秒或8秒 - 就像periscope如何淡出直播中的消息一样。这是我的代码的相关部分：

override func cellForItem(at index: Int) -> UICollectionViewCell {
    // ...

    // Get the time interval since the message was posted
    let timeInterval = 11 - Date().timeIntervalSince(message.timestamp)

    // If within the last 3 seconds, begin a fade.
    if timeInterval <= 3, timeInterval > 0 {
        cell.alpha = CGFloat(1 - 3/timeInterval)
        cell.fadeAlpha(to: 0, duration: timeInterval) { finished in
            if finished {
                self.delegate?.removeMessage(withSectionController: self)
            }
        }
    } else if timeInterval <= 0 {
        // If 11 secs or more have passed, remove.
        self.delegate?.removeMessage(...)
        cell.alpha = 0
    } else {
        // Otherwise start a timer
        timer = Timer.scheduledTimer(timeInterval: timeInterval, target: self, selector: #selector(removeMessage), userInfo: nil, repeats: false)
    }
    return cell
}


@objc private func removeMessage() {
    timer.invalidate()
    // In other code I have got the cell
    // This is a UIView animation that changes the alpha
    cell.fadeAlpha(to: 0, duration: 3) { finished in
        if finished {
            self.delegate?.removeMessage(...)
        } else {
            // This gets cancelled on other cells when removeMessage gets called on a cell.
        }
    }
}


// In the delegate
func removeMessage(...) {
    model.messages.removeFirst()
    // This performs updates on the collection view data
    performUpdates()
}

...表示还有其他代码但不相关。

我的代码有效，除非我的集合视图更新单元格，否则会取消当前的淡入淡出。我该如何解决这个问题？

Answer 1

您应该将其实现为自定义UICollectionViewLayout。显示后，设置计时器以从模型中删除消息，并通过调用

删除单元格

deleteItems(at: [IndexPath])

在您想要淡出的项目的集合视图中。

在自定义布局中，您需要实现

finalLayoutAttributesForDisappearingItem(at itemIndexPath: IndexPath) -> UICollectionViewLayoutAttributes?

并返回UICollectionViewLayoutAttributes实例，并将alpha属性设置为0。

此方法指定从集合视图中删除项目时将设置为的属性。

如何在指定时间后淡出UICollectionViewCell

1 个答案: