Question

我想确保我的tableview只包含符合所述协议的单元格。我简化了实现以说明具体问题。

!vi

上面的代码是有效的，只是有重复的代码，我每次都需要进行转换来访问configureMyLookAndFeel（）方法。因为我希望我的所有单元格都配置为外观和感觉，我尝试了下面的代码，但是遇到了编译错误

错误：无法将'protocol'类型的返回表达式转换为返回类型'UITableViewCell'

    protocol ACommonLookAndFeel {
       func configureMyLookAndFeel() 
    }

    CellA: UITableViewCell, ACommonLookAndFeel
    CellB: UITableViewCell, ACommonLookAndFeel

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

        var cell: UITableViewCell   

        if indexPath.row == 0 {          
             cell = tableView.dequeueReusableCellWithIdentifier("CellA", forIndexPath: indexPath) as! CellA
             if let myCell = cell as? CellA {
                 myCell.configureMyLookAndFeel() // we need to call this for each cell
             }
        } else if indexPath.row == 1 {
            cell = tableView.dequeueReusableCellWithIdentifier("CellB", forIndexPath: indexPath) as! CellB
            if let myCell = cell as? CellB {
               myCell.configureMyLookAndFeel() // we need to call this for each cell
            }
        }
        return cell
     }

有没有办法解决这个编译错误？
理想情况下，我不想避免重复调用dequeueCell和强制转换为 CellA 或 CellB 。基于 cellReuseIdentifier ，我知道我需要将它投射到哪个单元格，这与我的单元格类名称相同。有办法吗？

谢谢！

Answer 1

试试这个：

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    var cell: UITableViewCell

    if indexPath.row == 0 {
        cell = tableView.dequeueReusableCellWithIdentifier("CellA", forIndexPath: indexPath) // There is no need to cast here
    } else if indexPath.row == 1 {
        cell = tableView.dequeueReusableCellWithIdentifier("CellB", forIndexPath: indexPath) // There is no need to cast here
    }

    // The method will be called for all cells that conform to ACommonLookAndFeel.
    // This is also safe, so no crash will occur if you dequeue a cell that 
    // doesn't conform to ACommonLookAndFeel. Depending on the behavior
    // you want to achieve, you may want to use a ! instead of ? to force
    // a crash in case of issues while developing your app.
    (cell as? ACommonLookAndFeel)?.configureMyLookAndFeel()

    // You have to return a UITableViewCell, not a ACommonLookAndFeel
    return cell 
}

如何使符合已定义协议的UITableViewCells出列

1 个答案: