ios - 无法返回 cellForRowAtIndexPath 中的单元格

Question

我正在尝试返回 tableView 中的不同单元格。通常在这种情况下，我会返回不同的单元格，然后在底部返回 nil，但在这种情况下，它会给我错误。我也试过返回一个空单元格，但也给了我错误。

我尝试过的

return nil

和

 var cell: UITableViewCell!
  return cell

但都返回错误。我该如何解决这个问题？

cellForRowAtIndex

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

    
    
    
    if indexPath.row == 0 {


        let cell: UITableViewCell = tableView.dequeueReusableCellWithIdentifier("imageCell", forIndexPath: indexPath) as UITableViewCell
        var imageFile = cell.viewWithTag(100) as PFImageView
        imageFile.image = itemFile


        cell.selectionStyle = UITableViewCellSelectionStyle.None
        return cell
        
    } else if indexPath.row == 1 {
        let cell: UITableViewCell = tableView.dequeueReusableCellWithIdentifier("segmentCell", forIndexPath: indexPath) as UITableViewCell
        
        var titleLabel = cell.viewWithTag(101) as UILabel?
        titleLabel?.text = itemTitle
        
        let segmentControl = cell.viewWithTag(102) as UISegmentedControl
        segmentControl.selectedSegmentIndex = segment
        segmentControl.setTitle("Beskrivelse", forSegmentAtIndex: 0)
        segmentControl.setTitle("Sælger", forSegmentAtIndex: 1)
        segmentControl.setTitle("Lokation", forSegmentAtIndex: 2)
        segmentControl.tintColor = UIColor(rgba: "#619e00")
        var font = UIFont(name: "Lato-Regular", size: 11)
        var attributes:NSDictionary = NSDictionary(object: font , forKey: NSFontAttributeName)
        segmentControl.setTitleTextAttributes(attributes, forState: UIControlState.Normal)
        segmentControl.addTarget(self, action: "segmentAction:", forControlEvents: .ValueChanged)
        

        cell.selectionStyle = UITableViewCellSelectionStyle.None
        
        return cell
      
    } else if indexPath.row == 2 {
        switch segment {
        case 0:
            let cell = tableView.dequeueReusableCellWithIdentifier("CellZero", forIndexPath: indexPath) as DescViewCell
            return cell
        case 1:
            let cell = tableView.dequeueReusableCellWithIdentifier("CellOne", forIndexPath: indexPath) as SellerViewCell
            return cell
        case 2:
            let cell = tableView.dequeueReusableCellWithIdentifier("CellTwo", forIndexPath: indexPath) as LocationViewCell
            return cell
        default:
            break
        
        }
    }
        
    
    var cell: UITableViewCell!
    return cell
}

Answer 1

如 previous answer for a similar question 中所示, -tableView:cellForRowAtIndexPath: 必须返回一个 UITableViewCell。所以你不能返回nil。但是，我还建议在使用 if else 或 switch 语句时避免在 -tableView:cellForRowAtIndexPath: 末尾返回以下代码里面:

//bad code design
var cell: UITableViewCell!
return cell

或:

//bad code design
var cell: UITableViewCell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as UITableViewCell
return cell

您可以编写比创建一个永远不会被调用只是为了让 Xcode 警告静音的 UITableViewCell 实例更好的代码!

那么解决方案是什么？

关键是要确保 if else 语句的最后一个可能值是在 else 中设置的(而不是在 else if 中).同样，关键是要确保 switch 语句的最后一个可能值是在 default: 中设置的(而不是在 case XXX:)。

因此，您的代码应如下所示:

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    if indexPath.row == 0 {
        let cell: UITableViewCell = tableView.dequeueReusableCellWithIdentifier("CellZero", forIndexPath: indexPath) as UITableViewCell
        /* ... */
        return cell
    } else if indexPath.row == 1 {
        let cell: UITableViewCell = tableView.dequeueReusableCellWithIdentifier("CellOne", forIndexPath: indexPath) as CellOne
        /* ... */
        return cell
    } else { //set your last indexPath.row case in "else", not in "else if indexPath.row == 2"!!!
        switch segment {
        case 0:
            let cell = tableView.dequeueReusableCellWithIdentifier("CellTwo", forIndexPath: indexPath) as CellTwo
            /* ... */
            return cell
        case 1:
            let cell = tableView.dequeueReusableCellWithIdentifier("CellThree", forIndexPath: indexPath) as CellThree
            /* ... */
            return cell
        default: //set your last segment case in "default:", not in "case 2:"!!!
            let cell = tableView.dequeueReusableCellWithIdentifier("CellFour", forIndexPath: indexPath) as CellFour
            /* ... */
            return cell
        }
    }
    //No need for a fictive "return cell" with this code!!!
}

如果 segment 不是可选的，多亏了 tuples，您甚至可以将之前的代码简化为:

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    switch (indexPath.row, segment) {
    case (0, _):
        let cell = tableView.dequeueReusableCellWithIdentifier("CellZero", forIndexPath: indexPath) as UITableViewCell
        /* ... */
        return cell
    case (1, _):
        let cell = tableView.dequeueReusableCellWithIdentifier("CellOne", forIndexPath: indexPath) as CellOne
        /* ... */
        return cell
    case (2, 0):
        let cell = tableView.dequeueReusableCellWithIdentifier("CellTwo", forIndexPath: indexPath) as CellTwo
        /* ... */
        return cell
    case (2, 1):
        let cell = tableView.dequeueReusableCellWithIdentifier("CellThree", forIndexPath: indexPath) as CellThree
        /* ... */
        return cell
    default: //case (2, 2)
        let cell = tableView.dequeueReusableCellWithIdentifier("CellFour", forIndexPath: indexPath) as CellFour
        /* ... */
        return cell
    }
}