Question

这个问题与这个帖子有关：how-to-set-the-height-of-a-cell-depending-on-a-uilabel-with-a-typewriter-effect

在我的tableViewController中，我的单元格包含UILabel，其打字效果由 setTextWithTypeAnimation 管理;

func configureCell(tableView: UITableView, cell: ParagraphTableViewCell, atIndexPath indexPath: IndexPath) {

    let paragraph = paragraphArray[indexPath.row] as! Paragraph
    cell.paragraph = paragraph

        self.queue = OperationQueue()

        let operation1 = BlockOperation(block: {

            cell.dialogueLabel.setTextWithTypeAnimation(typedText: paragraph.dialogueLabel.text!, queue:self.queue, callBackAfterCharacterInsertion: {

                self.tableView.beginUpdates()
                self.tableView.endUpdates()
            })

        })


    operation1.completionBlock = {

    cell.buttonsStackViewHeightConstraint.constant = CGFloat(HEIGHT_CONSTRAINT)

    UIView.animate(withDuration: 0.3, animations: {
        cell.contentView.layoutIfNeeded()
    }, completion: nil)

    }

    queue.addOperation(operation1)

   }

我的打字机位于UILabel扩展程序中：

extension UILabel {

func setTextWithTypeAnimation(typedText: String, queue: OperationQueue, characterInterval: TimeInterval = 0.05, callBackAfterCharacterInsertion:(()->())?) {

    text = ""

    for (_, character) in typedText.characters.enumerated() {

        if queue.isSuspended {

            OperationQueue.main.isSuspended = true
            OperationQueue.main.cancelAllOperations()
            break;
        }

        OperationQueue.main.addOperation {

            self.text = self.text! + String(character)
            callBackAfterCharacterInsertion?()

        }

        Thread.sleep(forTimeInterval: characterInterval)
    }
}
}

首先我使用DispatchQueue来管理单元格内的动画（参见how-to-set-the-height-of-a-cell-depending-on-a-uilabel-with-a-typewriter-effect），但是当用户关闭视图控制器时我需要停止该线程。这就是我使用OperationQueue（DispatchQueue无法停止）

的原因

@IBAction func closeViewController(sender: AnyObject) {

    dismiss(animated: true, completion: nil)

        if self.queue != nil {

            self.queue.isSuspended = true
            self.queue.cancelAllOperations()
            self.queue = nil
    }
}

问题是当调用completionBlock时，当我尝试更新布局约束时应用程序崩溃。

This application is modifying the autolayout engine from a background thread after the engine was accessed from the main thread.

如何避免此次崩溃？

Answer 1

您必须致电UI上的mainQueue内容。

示例：

operation1.completionBlock = {
    DispatchQueue.main.async {
        cell.buttonsStackViewHeightConstraint.constant = CGFloat(HEIGHT_CONSTRAINT)

        UIView.animate(withDuration: 0.3, animations: {
            cell.contentView.layoutIfNeeded()
        }, completion: nil)
    }
}

如何正确使用OperationQueue？

1 个答案: